FAQ Finder

MISP method to remove the matrix (unwanted substances in the sample) from the analyte.

The sample is injected into a stream of transfer solution (generally ultrapure water). The analytes are retained on the preconcentration column, and the matrix is then removed using an additional transfer solution. The analytes are injected after this cleaning.

Accessories

The following accessories are generally used to determine the oxidation stability of biodiesel (B100) and biodiesel blends:

• 6.1429.050 Reaction vessel long (250 mm)
• 6.2418.130 Air tube long (248 mm)
• 6.1428.030 Measuring vessel (glass)
• 6.1839.000 Iso-Versinic tubing

All the accessories required for 100 determinations are included in the scope of delivery of the 893 Professional Biodiesel Rancimat.

 

Standard method parameters
Sample amount	7.5 g
Measuring solution (water)	60 mL
Sample temperature	110 °C
Gas flow (air)	10 L/h
Evaluation	Induction time Automatic (2nd derivative) Optional (manual): tangential method

Detailed information on the maintenance work described below is given in the manual for your instrument.

Aspiration filter: The aspiration filter should be replaced if it is discolored or at least every three months. Contaminated aspiration filters can lead to pressure and baseline fluctuations.

IC pump: The piston, seals, and valves should be serviced at least once a year.

Inline Filter: The Inline Filter should be replaced if the backpressure increases or at least every three months.

Pulsation absorber: Maintenance is not possible. Defective pulsation absorbers must be replaced.

6-way injection valve: If there are problems with the precision, check the installation of the sample loop. More extensive maintenance should be carried out by a service technician.

Suppressor (MSM, MSM-LC, MSM-HC): If the capacity drops or a high backpressure builds up, the Suppressor Module must be regenerated, cleaned, or replaced.

Detector block (conductivity detector): A blocked inlet capillary can be shortened by a few millimeters. Backflushing with the high-pressure pump may also help. Caution: The pressure must be < 5 MPa. The detector block must not be opened under any circumstances.

Detector cell (amperometric detection): The working electrode can be cleaned and polished as described in the manual. The reference electrodes are maintenance-free. The Ag/AgCl reference electrode must be replaced at regular intervals.

The "User administration" has three predefined user groups ("Administrators", "Users", and "Removed users").

The only predefined user under "Administrators" is "Admin1". The first-time login as "Admin1" does not require a password. Assignment of a password is then prompted automatically afterwards. Administrators have full access permissions for all functions of MagIC Net, particularly for the exclusive editing of user management. The creation of a second administrator access is recommended so that, if one administrator is unintentionally deleted, the user management can still be edited.

Additional "Groups" can be created in addition to the existing group of "Users". The access permissions, signature permissions, and display standards can be freely assigned to these "Groups". Users created within these groups have the permissions assigned to the group. When a user is created, a start password must be assigned. This is a single-use password so that the user can log in once. The user is then prompted to change his or her password.

Inline preconcentration is a method in which the analyte is retained on a short column (the preconcentration column).

This preconcentration column is installed on the injector instead of the sample loop. When the injector is switched over, the preconcentrated analytes are sent to the separation column. Preconcentration is mainly used for very low concentrations (ng/L to µg/L range). It enables preconcentration of analytes from large sample volumes. A Dosino (e.g., with a 5 mL dosing unit) can be used in MiPCT setup for preconcentration of 44,000 µL of the sample solution, an automatic multipoint calibration using one standard solution, or a logical adjustment of the sample volume. This covers a concentration range of the samples of 1:1,000,000 (ng/L to mg/L).

If the air tube is always positioned in the same way, the reproducibility of the results improves.

Fitting without foam barrier
If you do not use a foam barrier, we recommend that you position the air tube in such a way that the bottom end does touch the glass wall of the reaction vessel. 

Fitting with foam barrier (6.1451.010)

If you use a foam barrier, the position of the air tube is fixed.

Note! You must ensure that the foam barrier is fitted in the upper half. The foam barrier can melt if it is too deep in the heating block during the measurement.

Databases containing a large number of determinations can become very large.

We thus recommend setting up a database management to limit the number and the size of the databases in MagIC Net. Thus databases can be created based on, e.g., weeks, months, projects, sample types, etc.

Databases that are currently not needed can be backed up and deleted from MagIC Net. The data remain as backup copies and can be restored at any time.

This means that the eluent flow rate is not constant. Possible reasons for this are

• A leak in the eluent path: Eliminate the leak.

• A blockage in the eluent path: Eliminate the blockage.

• Gas bubbles in the eluent: Degas the eluent and check the connectors of the eluent degasser.

• The high-pressure pump has contaminated valves: Clean or replace the pump valves.

• The high-pressure pump has defective piston seals: Replace the piston seals and, if necessary, the pistons.

After pressing [Stop], the Exit track is executed, but if you press [Stop] again, the Exit track will be interrupted. As a result, there will be no database entry.

Calibration method for very small concentration ranges (ng/L to µg/L) using a standard solution with a higher concentration that is easier to manage. This requires an additional injector and a preconcentration column.

Determinations are not stored as individual files, but in a database. They can, however, be exported from the database and stored as *.idet files. The *.idet files can be imported into other MagIC Net databases. The version of the receiving MagIC Net must be the same or higher.

There are two kinds of databases: configuration databases (ConfigDB) and determination databases.

They can easily be copied (e.g., onto CD-ROM for backup purposes) and restored at the new location.

However, please note the following: If the databases are opened, they are blocked for processing (deleting, overwriting, copying, etc.). ConfigDB is always opened by the tiamo services (Metrohm tiamo Admin Server and Metrohm tiamo server) − the other databases are opened only if tiamo or a backup is running.

Therefore, tiamo must be closed, and the backup server and the tiamo services must be stopped before you carry out any file operations. Bear in mind that for normal users the paths made available by tiamo (backup and restore) should be used.

• Brochure: Mercury Handling Guidelines
• http://en.wikipedia.org/wiki/Mercury_poisoning
• https://www.who.int/teams/environment-climate-change-and-health/chemical-safety-and-health/health-impacts/chemicals/mercury
• http://www.epa.gov/mercury/
• http://ec.europa.eu/environment/chemicals/mercury/index_en.htm

The potentiostat integrated in the Metrohm CVS instruments can easily measure the smallest current with a high degree of precision. For this reason, it is also possible to get precise measurement results with smaller platinum electrode tip diameters. In a few exceptional cases, the method parameters need to be adjusted.

The gas flow does not have a significant effect on the end result as long as it is ensured that the sample can be mixed well and the cooling effect is compensated for by correctly determining the temperature correction.

Technical poster

8.000.6081 (Determination of the oxidative stability of biodiesel (fatty acid methyl esters, FAME))

To prevent contamination of the Suppressor Module by foreign particles and bacterial growth, it is necessary to install the 2 µm Inline Filter (6.2821.120) contained in the scope of delivery between the peristaltic pump and the inlet capillaries of the Suppressor Module.

The molecular sieve can be regenerated at 300 °C in the drying oven. The regeneration time is at least 24 hours. The molecular sieve is then placed in a desiccator for cooling down and afterwards stored in a glass bottle with an airtight seal.

All MagIC Net versions incorporate a comprehensive user management that enables operation in full compliance with these rules and regulations. The minimum conformity settings can be activated with one mouse click.

The dosing units used must be prepared at least once a day before measuring begins. This ensures that fresh solution is used for the analysis.

Yes.

No, this is not possible.

The view used when the database is opened is set as follows:

• If a default view has been set in the user administration for this user group (the group to which the logged-on user belongs) then it will be used.
• The view stored when tiamo was last closed will otherwise be used.

A "batch" is a collection of different "Determinations" within a database.

The assignment of determinations to a "batch" can be carried out when entering the sample data at the workplace. An existing or a new batch name can be chosen. In the first case, the determinations are added to the selected "batch", and in the second case, a new "batch" is created. In the database, it is also possible to create or delete a "batch" or to add existing determinations to a "batch".

These determinations can be simply filtered out of the whole set of determinations using the batch names. The batch assignment is used for fast viewing of data that belong together. There are also further options, such as filters, etc., to find data.

The maximum batch size is 500 determinations. If an attempt is made to add more determinations, these will be ignored. New determinations are normally stored in the "Database". No data is lost.

If a "Batch" is deleted, only the links of the determinations to the "Batch" are deleted, but no data.

In the event of network interruptions, client enquiries to the database (Determination Start, Report, Database, and Export commands) are held until the database is accessible again (without time limit). Device processes are not affected − they continue to run.

The conductivity of the deionized water should not exceed 20 µS/cm. If the value measured at the start of the measurement is higher than this, it is indicative of a problem with the conductivity measuring cell. This is generally caused by the electrode being contaminated with sample residue. To avoid this, the measuring vessel and the conductivity measuring cell should be cleaned thoroughly after each determination (see Cleaning after the determination).

The electrode surface of the Ultra-Trace electrode can be regenerated with the special polishing set, art. no. 6.2802.020.

The example methods are saved as *.imet files during installation in a subdirectory of the program directory.

If such an example method is to be used, it must be imported using "Method manager" into a "Method group". If this method is to be used directly with the existing IC system, the same devices and module names must be used. If "Common variables" are used in the method, they must be created first under "Configuration".

Devices, intelligent modules, and components are automatically detected by MagIC Net and registered under "Configuration". As soon as a new component is detected, a window appears in which the individual details can be adjusted.

Non-intelligent components and accessories can be registered manually in the appropriate category. This allows monitoring of all parts in the IC system that must be maintained or replaced at regular intervals.

A Method is used to define what, how, and when something is carried out and determined.

In MagIC Net, the method is composed of four windows.

"Devices" shows all instruments and modules used in the method along with their parameters. Clicking on the corresponding icon opens the parameters of this component so they can be adjusted.The "Analysis" is also created in this window. "Hardware assignment", "Data acquisition", and "Accessories" are defined here. The window "Evaluation – Components" has the sections Integration, Analysis Components, Standards, Calibration, and Results. Under "Results", it is possible to define "User-defined results", "Statistics", "Monitoring", etc. The third method window, "Time program", defines the exact analysis run. This defines all steps that the IC system or MagIC Net must execute. A time program can comprise a few consecutive steps or complex interleaving of subprograms. The fourth window shows the last chromatogram with the current calibration.

Port 3 of the dosing unit used can be connected to a waste canister using an outlet tubing. The outlet (port) 3 can be defined for the waste in the software (General settings or Configuration). With these settings, a significantly quicker preparation is ensured.

Separation columns that are not being used must always be sealed and filled in accordance with the manufacturer's instructions before being stored. If there is no information available, the separation column should be stored in a refrigerator at 4–8°C

In the case of two-component-reagents, the water capacity is limited by the amount of SO2 and buffer in the solvent. Decreasing pH values and decreasing SO2 concentrations result in a drop in titration speed. Reagent manufacturers have published the following guideline: The cell solution should be replaced after approximately 30 mL of titrant have been used in the case of cell solutions with 20 to 25 mL of solvent.

One-component reagents have no limiting water capacity, because SO2 and buffer are added with the titrant. Care must nevertheless be taken to ensure that the methanol content does not drop below 25%, because otherwise the endpoint will be shifted.

Info: The water capacity indicates how much water can be determined in a particular titration solution.

Coulometric KF reagents contain iodide instead of iodine. Additional components are sulfur dioxide and imidazole, which are dissolved in methanol. Generally, coulometric KF reagents have a water capacity of 1000 mg H2O per 100 mL. Depending on the type of reagent the water capacity can also be lower.

There is a leak in the system. Please check all connections.

Global − the following data is global, i.e., visible in all clients: methods, determinations, export templates, report templates, audit trails, sample tables.

Client-specific − the following data is client-specific, i.e., only visible in the client in question: configurations, views, ID text templates, sample allocation tables.

NB: The data, including client-specific data, is always stored in the database on the server.

It is possible to count the sample injections in MagIC Net. As soon as the corresponding number is reached, you can use the "Time program command">"Insert new line" in the "Sample table" to insert a sample line with the data of the sample for a check standard.

You can prepare your own standard solutions from the appropriate salts or you can buy them directly from a chemicals supplier.

Please check that the pH value of the solutions is suitable for the respective separation columns. Standards and reagents especially for ion chromatography can be found for example here

If the sample amount ranges between the minimum and maximum amount possible (see What is the smallest and what is the largest sample amount that I can use for the determination?), an error of ±10% of the sample weight is irrelevant.

Technical poster

8.000.6081 (Determination of the oxidative stability of biodiesel (fatty acid methyl esters, FAME))

The recovery rate can be calculated if a determination of the sample type "Spiking" is carried out after the "Sample".

The concentrations of the spiking solution are defined in the method. More than one spiking solution can be defined.

tiamo backs up all data in a database − there is no intermediate storage of files.

Files are only created by means of the commands EXPORT (mdet, xml, csv, slk) or REPORT (pdf). This data, however, is secondary data, i.e., copies of the original determination.

The data that ends up in the determination database never undergoes intermediate storage and is thus protected against changes.

The electrode cable has accidentally been jammed in the measuring head cover or a cable contact has been bent: On the 894 Professional CVS you can replace the electrode cable set (see 894 Professional CVS manual). On the 797 VA Computrace this needs to be handled by Metrohm Service.

Crystals have formed (in the dosing cylinder, on the valve disk or in the capillary):

• Check the flow path.
• Rinse the dosing unit and the connected tubing and capillaries (prepare function) when the measuring system is not in use.
• Clean the dosing unit at least every two weeks.

There are a number of possible reasons for a pressure increase in the system. First of all, find out the location of the pressure increase. The best way to do this is to remove one system component at a time from the flow path, starting from the eluent outlet, and check the measured pressure difference. The component causing the pressure increase must then be serviced or replaced. Typical components that can cause a high backpressure are:

• The Inline Filter (6.2821.120): The filter disk (6.2821.130) can be replaced.

• The guard column: Replace the guard column.

• The separation column: Regenerate the separation column according to the column leaflet (should be carried out only if the separation or peak shapes are affected as well). Note: Separation columns should always be operated with a guard column. Samples should always be microfiltered.

• The injector: If the increased backpressure is caused by the injector, you should have it cleaned by a Metrohm Service technician.

The solutions should be protected from direct sunlight. If possible, the solutions should be stored in glass vessels. Unless specified otherwise, additives should be stored at room temperature.

If you want to change this you must do so in the device's Titrino configuration: [CONFIG]; Set >Prep. Dosing Elements; Dose.Drive to Dosino. With this device the serial number cannot be read out.

The working electrode needs to be cleaned. Carry out a conditioning procedure in pure VMS. If applicable, the electrode needs to be cleaned.

Our electrode finder helps you to find the ideal electrode for your titration in just a few clicks.

Go to the electrode finder

After recalculation the result disappears from the view. This is not a bug, but can occur if the database view has been filtered. After recalculation the view is updated, thus a result can «disappear». In this case, the filter must be reset or changed.

In the safety settings, under «Logoff» the option «No processing of workplaces in the BUSY status» must be ticked.

The following prerequisites must be met for the backup function to work:

• BackupServer.exe must be running (check in Task Manager).
• On the server (tiamo multi license) or on the client (tiamo full or light license) a user with appropriate rights must be logged on and remain in Windows.
• This user plus the system user need at least Modify rights for the backup and database directories.
• In the backup directory there must be sufficient space free to create a new copy of the database. The old backup will not be deleted unless this copy has been created. tiamo will thus temporarily need more space.
• The firewall settings must be correct (see «General»).

The reference electrode is not yet equilibrated: After maintenance of the reference electrode, wait for at least 20 min before starting a measurement.

The platinum electrode tip is contaminated: Condition the working electrode in pure VMS.

The platinum electrode tip has been used for a very long time: Immerse the platinum electrode tip in c(NaOH) = 0.5 mol/L for approx. 10 min and then thoroughly rinse with distilled water. Replace the platinum electrode tip if necessary.

The VMS is contaminated: Check whether the reagents are clean. Only reagents with degree of purity "analytical grade" or better should be used.

The water quality is poor: Use distilled water, type-II grade (ASTM D1193-91) or higher.

The measuring solution is contaminated by diffusion: No infeed tubing other than the four-way micro dosing tip (6.1824.000) may be immersed in the measuring solution.

The cell constant of the conductivity measuring cell used in the Rancimat lies between 1.0 and 1.2 cm-1. For measurements in which the induction time is to be determined, more precise calibration is not required, as only the relative change in conductivity is evaluated in the case of the induction time.

If, however, the stability time is to be determined, in which the absolute change in conductivity is evaluated, we recommend that you determine the cell constants. You can find more detailed information on working with calibrated conductivity measuring cells and determining the cell constants in the manuals for your instrument and the software used.

The columns may only be used in the flow direction. A guard column should always be used. This must be replaced at regular intervals (in the case of a Metrosep RP 2 Guard, only the filter and the frit may need to be replaced). To increase the service life of a separation column, check, e.g., the quality of the chemicals used, the water, and sample preparation (e.g., filtered or dialyzed samples).

The electrolyte vessel can be filled with any electrolyte that is a good conductor. If chloride interferes with the determination, you can use KNO3, for example, instead of KCl. However, you should not change the electrolyte in the internal reference system. Using a different electrolyte here instead of c(KCl) = 3 mol/L changes the reference potential. This is also the case if you are using a different concentration of KCl.

During measurement, sample components may be absorbed by the plastic. This occurs in particular when measuring biodiesel and can cause the cover to expand. An important measure for counteracting this is to heat the cover after cleaning (see Cleaning after the determination). If heating the cover still does not enable a seal to be formed with the reaction vessel when it is closed, the cover must be replaced.

Metrohm offers service agreements tailored to your requirements. These range from standard maintenance with a priority response time to full support with an all-inclusive package and a guaranteed response time.

The temperature is the measuring parameter that has the greatest effect on the end result (induction time, stability time). If the temperature is not prescribed by a standard, the sample temperature should be selected in such a way that the result lies between 4 and 10 hours.
As a general rule:

• If the sample temperature is increased by 10 °C, the induction time halves.
• If the sample temperature is decreased by 10 °C, the induction time doubles.

Technical poster

8.000.6081 (Determination of the oxidative stability of biodiesel (fatty acid methyl esters, FAME))

tiamo is only installed in the program directory. The databases and backups are set up in the paths selected by the user during the installation procedure. Additional data (logs, etc.) is stored in the ProgramData directory (All Users\Metrohm).

Both the Multi-Mode Electrode and the Multi-Mode Electrode pro can be operated using a maximum of 6 mL mercury (roughly equal to 81.2 g). This amount is sufficient for approx. 200000 drops.

The peak type of each component peak is determined with a result variable (type). The peak type can be displayed using a user-defined result. The peak type is written as a combination of two or more letters. The first two letters describe the start and end of the peak. A two-letter output shows that the peak was integrated automatically. In case of manual integration, the next letter is an M (e.g. BBM, DBHM, etc.).

The cables are not connected or not connected correctly:

• Connect the cables in accordance with the instructions in the manual.

The tubing connections are leaking:

• Check the tubing connections and tighten, if necessary.

The rinse and/or waste canister are sealed air-tight:

• Loosen the caps on the canisters a little or remove them.

With local installations (light and full) such problems can occur if the processor load is constantly high (>80%). This situation, however, is unusual, and therefore the on-site administrator should check why the processor is so overloaded. Normally the processor workload is >10%, with load peaks in between.

With a multi system the reasons for this may vary: server load very high, the network is unstable, above all under load (low response times), the network connection has briefly been interrupted.

Most likely, the VMS in the measuring vessel is contaminated. The contamination might have been caused by the chemicals used but also by organic additives.

Yes. See also «The more data there is, the slower tiamo becomes», under Databases in general.

The analytical quality attainable with Metrohm IC chiefly depends on the separation of the ions of interest on the deployed column.

When buying an IC column, you should make sure that it provides sufficient separation for the intended analytical samples. You can assess this using the reference chromatograms in the Column Catalog.

If problems should occur during your analyses, the first step is always to check the quality of the column and record a standard chromatogram. Compare the data on the column leaflet, e.g., retention factors, selectivity, number of plates, and resolution, with your own measurements.

Further information on handling IC separation columns is given in the brochures supplied with the column, in the Column Catalog, or in our column finder.

Column Finder

Statistics functions are available in the method for multiple injections. They can be used to calculate the mean value, the absolute and relative standard deviation as well as the minimum and maximum value of a "Result".

A correct reference potential of the reference electrode is an important factor for perfect results in CVS analysis. We recommended that you change the reference electrolyte c(KCl) = 3 mol/L at least every three days.

The problem can be rectified as follows: Go to the Windows system properties and select «System performance». Then select the «Expand» tab and click on [Settings]. The «Performance options» dialog will then be displayed. Select the «Visual effects» tab and deselect the «Show window content when dragging» checkbox.

 

Solid samples must be broken up before they are weighed into the reaction vessel. The particle size should be as uniform as possible.

Samples of this type are not mixed by the air flow during the determination. Only a small sample amount should be used to avoid a nonhomogeneous temperature distribution within the sample. We recommend selecting the sample amount in such a way that the base of the reaction vessel is covered evenly. A sample amount of 0.5 g is frequently used.

We also recommend using shorter air tubes for PVC (140 mm, order number 6.2418.120) with solid samples.

Dirty platinum pins can be cleaned with an abrasive agent such as Alox (polishing set, art. no. 6.2802.000) or toothpaste. Afterwards, they should be rinsed with ethanol or methanol. It is often sufficient to wipe off the indicator electrode with a soft paper tissue. This is particularly important when the electrode was immersed previously in an overtitrated solution, because deposits can form there that are not visible but nevertheless lead to overtitrations. If the sample itself adheres to the electrode, clean it off, either with an appropriate solvent or mechanically. Clean the platinum pins on the indicator electrode with a soft paper tissue and take care to ensure that the pins do not become deformed (pressed together) while doing so. They should always be parallel to one another.

If a titrator with Dosing Unit is not used for several days, then it is best to empty the Dosing Unit with the «Empty» command. In this way, you will avoid the formation of crystals in the Dosing Unit, the tubing, and the buret tip (antidiffusion valve).

If work is being done with an Exchange Unit, then you should immerse the buret tip in methanol in order to avoid crystallization. To accomplish this, you can either fill the storage vessel with methanol or continue to leave the buret tip in the closed cell filled with working medium, where it is immersed in the working fluid.

The Exchange Unit, the tubing, and the buret tip should all first visually inspected for crystals before the system is returned to operation. If crystals are present, then the tubing should be flushed with methanol or ethanol and then dried afterwards.

If no crystals are visible, then a small amount of reagent should nevertheless be dosed in order to check whether crystals have formed in the flat stopcock of the Exchange Unit. If reagent escapes from the flat stopcock, then the Exchange Unit must be disassembled and cleaned (see manual for the Exchange Unit).

Afterwards, flush the Exchange Unit by means of the Preparation/«Prep» command in order to make it ready for operation again.

We advise against mechanical treatment of platinum electrodes, e.g., by polishing with aluminum oxide!

The dosing units available for the 800 Dosino have volumes of 2 mL, 5 mL, 10 mL, 20 mL, and 50 mL. Since the 800 Dosino doses the total volume in 10,000 increments, the unit with the smallest possible volume should generally be used to obtain the highest possible accuracy.

We recommend the following:

• Eluent preparation: 50 mL dosing unit
• MIDT: 10 mL dosing unit
• MiPCT, MiPCT-ME: 5 mL dosing unit
• MiPuT, MiPT, suppressor regeneration: 2 mL dosing unit

Results may be too low for the following reasons:

 

Cause	Remedy
Side reaction	Read for more details in the following FAQ: «How to recognize a side reaction?», «How to prevent side reactions?»
The sample is inhomogeneous	Increase the sample size. Homogenize the sample prior to the determination.
The sample dissolves incompletely	Read for more details in the following FAQ: «What can I do to improve the release of water?»
The pretreatment of the sample is not optimal.	Read for more details in the following FAQ: «What to do to improve the release of water?»
Titer is incorrect (volumetric KF titration)	Redetermine the titer with certified standards.
Titration stops too soon	Reduce Stop Drift or work with a relative Start Drift.
The sample gives off water even during sample preparation	Here we recommend optimizing the sampling and sample storage, as well as rapid working during the determination sequence.

Trend within the results

One reason for decreasing water contents in a series may be that the solvent is exhausted and must be replaced. Decreasing water contents within a series can also occur with samples which give off water during sample handling. Here we recommend optimizing the sampling and sample storage, as well as rapid working during the determination sequence.

A further possible reason for apparently decreasing water contents within a series in volumetric Karl Fischer titration is that the buret has not been prepared. The titrant in the cylinder and in the tubing is exposed to humidity, which can result in increased titrant consumption at the beginning of a series.
Increasing water contents within a series can occur with hygroscopic samples. Here we recommend optimizing the sampling and sample storage, as well as rapid working during the determination sequence.

Tip: You can recognize very quickly whether your sample is either releasing water, is hygroscopic, or unproblematic by determining the water content of the sample immediately and then leaving the sample to stand in a beaker in the laboratory air and determining the water content again after 10, 30, and 60 minutes.

A loud pump noise indicates that a large pump capacity is required to achieve the set gas flow. This can be caused by either a leak or a blockage in the feed lines to the pump. You should keep track of the cause, as it increases wear and therefore reduces the pump service life in the long run.

Possible leaks:

• Tubing connections on the rear of the instrument are not screwed tightly enough. Tighten connectors securely.
• One of the tubing connections on the rear of the instrument is defective. Replace tubing connection.
• The cover of the drying flask is not tightly screwed. Screw the cover on tightly.

Possible blockages:

• The dust filter on the rear of the instrument is clogged. Replace filter, see also Regular maintenance – Dust filter (6.2724.010).
• The filter tube (6.1821.040) in the drying flask is clogged due to dust from the molecular sieve. Remove dust by tapping out the filter tube. Replace the aspiration filter (6.2821.090), if necessary.

This effect is not uncommon. It is caused by degradation products in the bath sample. With successful determination of recovery in a "check standard", the method can be checked at any time.

All Metrohm Service technicians must undergo extensive service training and are certified by specially qualified trainers. Metrohm Service technicians have a corresponding service pass that is valid for two years.

Up-to-date information on the compatibility of MagIC Net with the individual Windows™ versions can be found in the Metrohm Software Center.

Select the determinations of this standard in the "Database" as well as all determinations of samples that are to be recalculated. In the "Determinations" menu, select "Reprocessing…" or click the corresponding icon. Select the affected standard in the "Reprocessing table" and open the reprocessing of sample data by double-clicking or via "Edit">"Edit line". Correct the "sample type" and then select "Apply" and "Close". Select "Reprocessing" and then the option "From the standards of the reprocessing table". All the determinations are recalculated using the parameters of the selected line. If the result of the reprocessing is satisfactory, save the reprocessed determinations by closing the reprocessing window with "OK". The procedure for further problems during "Reprocessing" is described in the online help under "How to proceed?".

No, harmful indicators are not used.

The background conductivity is defined by the eluents and the suppression reaction. This means that the eluent composition may be incorrect or suppression is incomplete. If suppression is used, make sure that the suppressors (MSM and MCS, if present) are connected correctly. Check the flow of the regeneration solution and the rinsing solution.

Because with tiamo 2.X the USB driver versions 1.5 to 2.4 are reset, problems with the following software types may ensue (device recognition):

• PC Control 1.0, 2.0, 3.0, 4.0, 4.1 (5.0 not affected)
• Mix Control 1.0, 1.1 (1.2 not affected)
• tiamo 1.0, 1.1, 1.2, 1.2.1 (1.3 not affected)
• MagIC Net 1.0 (1.1 not affected)
• FlashBurn up to 3.1 (3.2 not affected)
• iService 1.0 (1.1 not affected)
• VA 797 version 1.0, 1.1, 1.2, 1.3 (1.3.1 not affected)

To make sure that these software types to continue to work correctly the user must be told to delete the file metr_770.dll in the directory %InstallationPath%\bin (of this affected software). If after installing tiamo 2.x you install one of the above softwares or repair an installation, you must subsequently again delete the file metr_770.dll in the directory %InstallationPath%\bin as above.

It is not possible to repair the driving axle. The driving axle is a consumable and needs to be replaced at regular intervals. Driving axles with a mercury contact are supplied in a bag under protective nitrogen atmosphere. We recommend keeping the storage time of driving axles with a mercury contact as short as possible.

All dosing units used should be rinsed with distilled water in order to prevent a possible crystallization of metal salts.

The tubes of a peristaltic pump are a consumable with a limited service life and should be replaced at regular intervals (approximately every 2 months if used continuously).

There are two different positions for attaching the tube. The position should be changed once a month.
The pressure of the tubing cartridge must not be too high: Increase the pressure incrementally until you can see that the liquid is flowing. Then increase the pressure with the contact pressure lever by a further two increments.

Use 3-stopper pump tubings with a longer service life: 6.1826.3X0 and 6.1826.4X0.

Inline Filters must be used for regeneration and rinsing solutions and must be replaced every three months or if the backpressure is too high.

As a temporary solution, you can replace the bridge electrolyte with a water-free electrolyte, e.g., c(LiCl) = 2 mol/L in ethanol.

We recommend a completely water-free reference electrode for permanent application. Both the reference system and the electrolyte vessel are filled with a water-free electrolyte. For this purpose, the internal reference system is also available dry with no electrolyte. The order number for this is 6.0728.010. The bridge electrolyte vessel 6.1245.010 is compatible with this.

c(tetrabutylammonium chloride) = 0.1 mol/L in acetonitrile, for example, is a suitable reference electrolyte. The electrolyte used for the application can be used as the bridge electrolyte. You must bear in mind that the electrode has a different reference potential with this reference electrolyte than with c(KCl) = 3 mol/L.

Caution! Reference systems with an LL Ag/AgCl system (6.0728.x30) are not suitable for use with acetonitrile.

Prepare the eluents with degassed and CO2-free ultrapure water. Dissolved CO2 can affect the pH and thus also the retention times.

If the drift during pretitration (conditioning) is too high after the addition of fresh working medium, then this is a sign that the titration cell is not protected sufficiently against humidity. Replace the molecular sieve and the septum. Also check to see whether all of the O-rings/PTFE sleeves are in proper condition.

MISP method for inline removal of particles, large molecules, oil droplets of emulsions, etc. from the sample solution prior to injection.

The "Stopped Flow" dialysis method, patented by Metrohm, is based on the diffusion of analyte ions from the sample stream into a stationary acceptor solution. The sample continues to flow through the cell during the dialysis period. Consequently, the sample concentrations in the dialysis cell always remain constant. Equilibrium between the sample and the acceptor solution is attained for practical purposes within a few minutes.

This means that the concentrations of sample ions are almost identical in both solutions. Since there is no pressure difference during dialysis, the driving force is purely diffusion. Thus the risk of blocking the membrane pores is even lower than for Inline Ultrafiltration.

Typical applications: heavily contaminated waste waters, dairy products, fruit juices, emulsions.

The contact pressure of the tubing cartridge is set too low: Set the contact pressure of the tubing cartridge in accordance with the sample changer manual.

The pump time of the peristaltic pump is increasing: The pump tubing of the peristaltic pump has aged or is defective and should be replaced.

The PEEK sample needle on the Sample Processor is positioned more than 0.5 mm from the bottom of the sample vial: Position the PEEK sample needle in accordance with the information in the manual.

All kinds of user groups (e.g., administrators, laboratory managers, laboratory technicians, etc.) can be defined in the user administration of MagIC Net.

Each of these groups can be individually assigned access permissions, signature permissions, and other options. Thus every group can be assigned access to precisely those functions that they really need.

Increased baseline noise can be caused by various components:

• The eluent is not sufficiently degassed: Make sure that the connectors of the eluent degasser are tightly connected.

• The eluent path has a leak: Check the connections.

• The high-pressure pump has contaminated valves: Clean or replace the pump valves.

• The high-pressure pump has defective piston seals: Replace the piston seals and, if necessary, the pistons.

• The pulsation absorber is not connected or is defective: Connect or replace the pulsation absorber.

• MCS – The CO2 cartridge is exhausted: Replace the CO2 cartridge.

• MCS – The vacuum pump is faulty: Please contact Metrohm Service.

• EN 14112 «Fatty acid methyl esters (FAME) – Determination of oxidation stability (accelerated oxidation test)»
• EN 15751 «Automotive fuels – Fatty acid methyl ester (FAME) fuel and blends with diesel fuel»
• EN 16568 «Automotive fuels – Fatty acid methyl esters (FAME) fuel and blends with diesel fuel – Determination of oxidation stability by rapidly accelerated oxidation method at 120 °C»

A. The electrodes are not well conditioned. Please perform a conditioning procedure on the electrodes.

B. The temperature is instable.

There is a "Sample table test" available for the sample tables.

 

If the method specifies a Dosino or a device that is connected to a Dosino, a query appears as to whether the Dosino should also be added to the method.

If the answer is yes, the name and use will be queried.

If you select "Suppressor Dosino", the Dosino can be used exclusively for "Dosino Regeneration". In this case, the Dosino is labeled in the diagram with an "S".

If you add a 941 Eluent Production Module, then you can define the Dosinos connected to it as "Eluent Dosinos". "Eluent Dosinos" are labeled with an "E".

Dosinos without a label ("S" or "E") are freely available for Liquid Handling tasks and are always selected as simple Dosinos.

If a Dosino is already defined in a method, it cannot be redefined. In this case, you must remove the Dosino from the method and then add it again as a new device. After you have defined the MSB connector, you can select its use.

 

MISP method for automatic sample extraction, e.g., extraction of ions from (bio)diesel.

Similar to MiPCT, but with additional Inline Matrix Elimination.

Platinum electrode tips with a glass shaft can be operated up to a maximum temperature of 50 °C.

Platinum electrode tips with a PEEK shaft can be operated up to a maximum temperature of 40 °C.

Metrohm does not recommend any mechanical treatment of platinum RDEs, e.g., by polishing with aluminum oxide!

The platinum electrode tip can be immersed for a few seconds in concentrated nitric acid to oxidize a metal coating which has accidentally been applied. If after another measurement foreign metal should be found on the surface again, then the method parameters and electrode connectors need to be checked.

Dosing and Exchange Units require regular checks and must be disassembled from time to time and cleaned if necessary. You will find a detailed description in the corresponding manuals.

Watch short video clips on how to clean the dosing unit

The following error message appears: «Printing error (017-117); an error has occurred during printing. Check the printer, the determination, or the report template». So far, this has always been because the paper tray in the printer was empty.

The following manufacturers offer KF reagents:

Honeywell:
www.hydranal-honeywell.com

Sigma-Aldrich:
http://www.sigmaaldrich.com/analytical-chromatography/titration/karl-fischer-titration.html

Here you will find the ordering information for the individual parts of your Multi-Mode Electrode pro (MME pro).

Here you will find the ordering information for the individual parts of your Multi-Mode Electrode (MME).

The solvent keeps flowing into the titration vessel after the addition, without the «addition» key being pressed.
Set the solvent bottle up in such a way that the fluid level in the bottle is lower than in the titration vessel.

Solvent is added simultaneously during aspiration.
The drying tube in the titration vessel is blocked:

• Enlarge the hole on the drying tube cover to at least 2 mm
• Refill the drying tube, do not pack too tightly, possibly remove some of the molecular sieve.

The pump conveys no fluid.
Press the «addition»/«aspiration» key more strongly.

• In most cases the bottle attachments are not screwed tightly enough to the reagent and waste bottles
• Check all connections for leak-tightness
• Check whether the 803 Ti Stand is set up correctly

If the gold electrode is used for trace analysis, then we advise against using any type of mechanical treatment, e.g., polishing with aluminum oxide!

Information regarding the preparation of the electrode can be found in the application instructions.

It is difficult to make a general statement concerning how often the molecular sieve should be replaced, because this is dependent on the humidity in the laboratory. Our experience has shown us that replacement every six weeks is appropriate in the presence of medium humidity. An increase in drift indicates that the leak-tightness of the cell should be inspected and that the molecular sieve should possibly be replaced.

Tip: Write the date on which you have last replaced the molecular sieve on the glass of the drying tube. In this way, you will always know when the next replacement is due.

A check box ("Stop hardware when sample table has finished") is located at the bottom right of the run window of the sample series.

If this check box is checked, the device is stopped automatically. This setting is stored for each workplace. Different systems running at different workplaces on one computer can thus be set up differently.

Volumetric KF titration

The sample size depends on the water content of the sample. In principle, the sample size should be selected in such a way that the titrant consumption lies between 10% and 90% of the buret volume. This means that if work is being done with a 10 mL Exchange or Dosing Unit, the consumption level of the titrant should be between 1 and 9 mL.

In addition, you should take care to ensure that the sample weight selected is not too low. The weighing error will be too great on the one hand, while on the other the sample will no longer be representative. In cases of high water content, it may be better to use a Dosing or Exchange Unit with a greater buret volume in order to avoid filling the Exchange Unit during the titration.

If the sample does not dissolve completely in the working medium, then the sample size has perhaps been selected too high and exceeds the dissolving capacity of the working medium. This can be remedied through the use of a smaller Dosing/Exchange Unit or a titrant with a lower water equivalent, e.g., 2 mg/mL or 1 mg/mL. Despite the lower initial weight, the titrant consumption will then achieve 10 to 90% of the buret volume.

As a general rule: When the titrant consumption is low, you should work with a lower titer (e.g., Titrant 1, Titrant 2), and with a high titer when titrant consumption is a high (Titrant 5).

Table: Recommended sample size

Sample	Approximate sample size [g] for 5 mL buret
Expected water content	Titrant 1	Titrant 2	Titrant 5
0.5%	0.1–0.9	0.2–1.8	0.5–4.5
1.0%	0.05–0.45	0.1–0.9	0.25–2.25
5.0%	–	0.02–0.18	0.05–0.45
10.0%	–	–	0.025–0.225
25.0%	–	–	–
50.0%	–	–	–

 

Sample	Approximate sample size [g] for 10 mL buret
Expected water content	Titrant 1	Titrant 2	Titrant 5
0.5%	0.2–1.8	0.4–3.6	–
1.0%	0.1–0.9	0.2–1.8	0.5–4.5
5.0%	0.02–0.18	0.4–0.36	0.1–0.9
10.0%	–	0.02–0.18	0.05–0.45
25.0%	–	–	0.02–0.18
50.0%	–	–	0.02–0.09

 

Sample	Approximate sample size [g] for 20 mL buret
Expected water content	Titrant 1	Titrant 2	Titrant 5
0.5%	0.4–3.6	–	–
1.0%	0.2–1.8	0.4–3.6	–
5.0%	0.04–0.36	0.8–0.72	0.2–1.8
10.0%	0.02–0.18	0.04–0.36	0.1–0.9
25.0%	–	0.016–0.144	0.04–0.36
50.0%	–	–	0.02–0.18

 

Coulometric KF titration

The sample size depends on the water content and should be small in order to allow you to titrate as many samples as possible in the same reagent and to keep the determination time short. However, ensure that the sample contains at least 50 µg of H2O.

The following table provides an indication of the sample size.

Water content of the sample	Sample size	H2O, to be determined (water content)
10000 ppm = 1%	10 mg–100 mg	100 µg–1000 µg
1000 ppm = 0.1%	100 mg–1 g	100 µg–1000 µg
100 ppm = 0.01%	1 g	100 µg
10 ppm = 0.001%	5 g	50 µg

 

The 800 Dosino was not attached correctly:

• Remove the 800 Dosino and attach it again.
• Check whether the 800 Dosino is correctly attached.
• Disconnect the CVS measuring instrument from the power supply and connect it again.
• If necessary, contact Metrohm Service.

The bridge electrolyte forms an electrical bridge between the measuring solution and the reference electrode. In many cases a strongly acidic measuring solution is used in CVS analysis. Over time, the acid may also reach the bridge electrolyte and thereby change the reference potential. This is why changing the bridge electrolyte every day is recommended. The reference electrodes filled with KCl gel are maintenance-free, which means that no electrolyte needs to/may be changed.

Always use only ultrapure water (Grade I, 18.2 MOhm at 25°C) for eluents, dilutions, and all other solutions that will be used for IC.

Eluents must always be prepared with analytical grade chemicals (i.e., with at least purity grade "p.a." or "analytical grade").

Freshly prepared eluents must always be microfiltered (0.45 µm filter) and then degassed with N2, He, or in a vacuum or with an inline degasser. If possible, a CO2 absorber should be used for basic eluents and eluents with a low buffer capacity.

The database comprises a directory with subordinate files and subdirectories. The database directory name is used in tiamo as a database name.

It is recommended that you repeat annually the testing of the instruments used for determining water content according to the Karl Fischer method. If an instrument is in continuous use, then more frequent testing intervals may be called for, e.g., every 6 months or even every 3 months. Unscheduled validations are called for when one or more components of the titration system have been replaced.

One reason for peak broadening is additional dead volume. This can occur if the capillary connections are not optimal and with old separation columns. Check the connections. If the dead volume is in the column head, the separation column can be operated for a certain time in the opposite direction (provided that this is permitted according to the column leaflet), otherwise the separation column must be replaced.

A further reason could be contamination of the guard column and/or the separation column. Replace the guard column. If the separation column is contaminated, regeneration (according to the column leaflet) may help. Otherwise, the separation column must also be replaced.

MISP method to add a known quantity of ions to a sample during preconcentration.

Typical application: check of recovery rates in a preconcentration system.

Here you will learn what is to be done if the reference electrode ever dries out.

The 6.0728.x40 reference system cannot be regenerated if it dries out. The electrode must be replaced.

Dried-out KCl gel cannot be removed from the electrolyte vessel. The electrolyte vessel must be replaced.

Once the gel filling of the electrode 6.0730.x00 has dried up, the gel reference electrode is irrevocably damaged and must be replaced!

A. It is usually sufficient to clean the platinum pins of the electrode with a soft paper tissue. However, you should take care to ensure while doing so that the platinum pins are not pressed together. They should always be parallel to one another.

B. In volumetric KF titration, the antidiffusion valve on the buret tip should be checked.

See the photo: good buret tip in comparison with defective buret tips

C. Check if you are using the recommended parameters:

Volumetric KF titration

 

	Ethanol-containing reagents	Methanol-containing reagents
Polarization current Ipol	20 µA	50 µA
Endpoint indication at	500 mV	250 mV

Coulometric KF titration

	Ethanol-containing reagents	Methanol-containing reagents
Polarization current Ipol	10 µA	10 µA
Endpoint indication at	20 mV	50 mV

D. A further cause of overtitration could be that the initial solution no longer contains sufficient methanol or ethanol. In such a case it is worthwhile to renew the cell solution and/or to check whether too much solubility promoter has been used. Read for more details in the following FAQ: «How often must the KF working medium be replaced?».

See table: Solubility promoters for volumetric and for coulometric titration

Volumetric KF titration

Solvent	Percentage	Samples
Formamide	max. 50%	Sugar samples, salts
Chloroform	max. 70%	Oil, grease
Long-chain alcohols	max. 50%	Oil, grease
Xylene, toluene	max. 70%	Crude oils with tars

Coulometric KF titration

Solvent	Percentage	Samples
Formamide*	max. 20%	Sugar samples, salts
Chloroform**	max. 30%	Oil, grease
Long-chain alcohols**	max. 30%	Oil, grease
Xylene, toluene**	max. 30%	Crude oils with tars

 
* Only with generator electrode without diaphragm.
** Use generator electrode with diaphragm if the amount of solubility promoter is higher than 10%.

Additional measures:

E. Increasing the stirring rate.
F. Check whether the platinum pins of the electrode are immersed completely in the cell solution.
G. Check whether the correct reagents were combined: if the titrant of the two-component reagent is used with methanol, the KF reaction cannot take place, because no SO2 is available for the reaction. (Only volumetric KF titration.)

	Sample size for 5 mL buret
Type of standard	Titrant 1	Titrant 2	Titrant 5
Water standard 10 mg/g	0.05–0.45 g	0.1–0.9 g	0.25–2.25 g
Na tartrate 156.6 mg/g		0.006–0.057 g	0.03–0.27 g
Water 1000 mg/g	–	–	~ 0.02 g
Water	–	–	~ 20 µL

 

	Sample size for 10 mL buret
Type of standard	Titrant 1	Titrant 2	Titrant 5
Water standard 10 mg/g	0.1–0.9 g	0.2–1.8 g	0.5–4.5 g
Na tartrate 156.6 mg/g	0.02–0.057 g	0.013–0.115 g	0.03–0.287 g
Water 1000 mg/g	–	~ 0.015 g	~ 0.025 g
Water	–	~ 15 µL	~ 25 µL

 

	Sample size for 20 mL buret
Type of standard	Titrant 1	Titrant 2	Titrant 5
Water standard 10 mg/g	0.2–1.8 g	0.4–3.6 g	1–9 g
Na tartrate 156.6 mg/g	0.02–0.175 g	0.026–0.23 g	0.065–0.58 g
Water 1000 mg/g	–	0.02–0.035 g	0.02–0.09 g
Water	–	15–35 µL	15–90 µL

You must ensure that the PTFE tubing does not feed the air directly onto the conductivity measuring cell. If gas bubbles are released onto the electrode, then this results in noisy measurement curves.

PTFE tubing position OK:

 

PTFE tubing position not OK:

 

GLP (Good Laboratory Practice) requires, among other things, periodic checking of the analytical instruments for their reproducibility and correctness on the basis of Standard Operating Procedures (SOPs). It is recommended that the instruments are qualified on a regular basis

For more information please contact us.

One or more electrodes are not connected: Check the electrode cable connections.

One or more electrodes are defective: Carry out maintenance according to the electrode data sheet. The measuring vessel does not contain enough solution or is empty: Check the fill level of the measuring vessel and add solution if required.

Accessories

The following accessories are generally used to determine the thermostability of PVC:

• 6.1429.040 Reaction vessel short (150 mm)
• 6.2418.120 Air tube PVC (140 mm)
• 6.1428.107 Measuring vessel (polystyrene)
• 6.1816.010 Silicone tubing

All the accessories required for more than 100 determinations are included in the scope of delivery of the 895 Professional PVC Thermomat. 

Standard method parameters
Sample amount	0.5 g
Measuring solution (water)	60 mL
Sample temperature	200 °C
Gas flow (air)	7 L/h
Evaluation	Stability time Conductivity change 50 µS/cm

For volumetric KF titration, a general distinction is made between one-component and two-component reagents:

One-component reagent		Two-component reagent
Working medium	Titrant	Working medium	Titrant
Methanol	Alcohol*/DEGEE** Base SO2 Iodine	Iodine Alcohol*	Alcohol* Base SO2
Advantages: A larger amount of solubility promoters can be added		Advantages: Stable titer, because reactive components are separated Quick reaction thanks to optimum pH value in the working medium
Disadvantages: Titer decreases approximately 5% per year in the closed bottle		Disadvantages: Limited water capacity

* Methanol or ethanol
** Diethylene glycol monoethyl ether

Reagents for coulometric KF titration contain iodide. The suitable reagent needs to be selected in accordance with the type of generator electrode (with or without diaphragm). For more information on the different types of coulometric KF reagents please refer to the manufacturers of KF reagents.

Results may be too high for the following reasons:

Cause	Remedy
Side reaction	Read for more details in the following FAQ: «How to recognize a side reaction? How to prevent side reactions?»
The sample is hygroscopic	Here we recommend optimizing the sampling and the sample storage as well as working speedily during the determination.
The sample is inhomogeneous	Increase the sample size. Homogenize the sample prior to the determination.
Overtitration	Read for more details in the following FAQ: «Overtitration took place, i.e., the titrated solution is dark yellow to brown instead of light yellow. How to prevent this?»
Only for volumetric KF titration:
The titer has changed since the last determination	Redetermine the titer.
Air bubbles in the tubing	Flush the tubing system using the Preparation/«Prep» command.
Non-leak-tight tubing system	Check for crystals in the tubing system. Check whether tubing is connected tightly. Check tubing connections.

Volumetric Karl Fischer Titration cell:

 

Coulometric Karl Fischer Titration cell:

 

Basic eluents can absorb CO2 from ambient air, which alters their pH value. This affects the retention times. Adsorption of CO2 can be prevented with a CO2 adsorber.

MISP method for filtration of sample solutions prior to injection.

The sample is fed past the filtration membrane. A pump is used to filter a small fraction of the sample stream through the membrane (partial vacuum) for subsequent analysis. The remainder of the sample stream flows into the waste container and simultaneously rinses the filtration membrane. This minimizes formation of a filter cake and thus a possible blockage of the membrane pores. Inline Dialysis can be used as an alternative if the samples are too heavily contaminated.

Typical applications: all samples that have to be filtered, e.g., natural waters (surface water, groundwater, wastewater, etc.).

Method using injection of different sample volumes using partial filling of the sample loop by a Dosino.

A multipoint calibration can be carried out with one standard solution. The injection volume can be adjusted for the sample. MiPT can be used for concentration ranges between µg/L and mg/L. Sample volumes between 2 and 200 µL can be reproducibly injected using a 250 µL sample loop.

The disodium tartrate dihydrate dissolves incompletely when several determinations are carried out in the same working medium because of the limited capacity of methanol to dissolve disodium tartrate dihydrate.

We recommend that you replace the working medium at shorter intervals.

The electrode surface of glassy carbon electrodes can be regenerated by polishing with aluminum oxide.

The method and the export and report templates are stored in the determination in addition to the data.

The database remains the same size as before. The freed-up space is now occupied by new data records, so the size of the database does not increase until the freed-up space has been filled again.

• MagIC Net Basic: This version is included in the scope of delivery of the 833 Basic IC plus.
• MagIC Net Compact: Version with one license for a sampler and either a Compact IC instrument, a detector, or a data channel (771 IC Interface).
• MagIC Net Professional: Version with one license for any number of devices at four workplaces on one computer.
• MagIC Net Multi: Client/server application with 3 licenses. Additional licenses can be purchased.

In the case of two-component-reagents, the water capacity is limited by the amount of SO2 and buffer in the solvent. Decreasing pH values and decreasing SO2 concentrations result in a drop in titration speed.

Reagent manufacturers have published the following guideline: In the case of cell solutions with 20 to 25 mL of solvent, the cell solution should be replaced after approximately 30 mL of titrant has been used.

1. Check the sample size.
2. Check whether the titer and concentration of the titrants are correct.
3. Check the calculation formula in the method. Is the correct equivalence point used for the calculation?
4. Check the system for air bubbles in the dosing cylinder and/or in the tubing connections.
5. Check whether the stirring rate is adequate. As a general rule, this should be as high as possible. However, try to avoid the formation of a vortex during stirring.
6. Check whether the titration might be too quick. You can use the titration parameters “signal drift” and “min./max. waiting time” to adjust the titration rate.
7. Check whether the sensor is still suitable for the titration. Sensors that are old or dirty can result in longer response times.

The "Audit Trail" is started automatically only if either "Settings according to 21 CFR Part11" or "Audit Trail active" are selected under "Security settings".

In case of an active "Audit Trail", a large amount of information is stored, which thus requires a lot of storage space on the computer. "Audit Trail" entries can be deleted after they have been archived. Deletion requires two "Signatures".

The data is always (even with local installations, i.e., light or full) transmitted unencoded via a TCP/IP interface.

The relative standard deviation of determinations with the Rancimat tends to be between 5 and 10%. The following points should be observed to keep scattering of the measurement results to a minimum:

• The sample must be homogeneous.
• Only use new reaction vessels and air tubes.
• Always position the air tube in the same way in the reaction vessel. See What do I need to keep in mind when positioning the air tube in the reaction vessel?
• Before weighing in the sample, remove any particles that may have adhered to the interior and exterior of the reaction vessel. See Preparation of the measuring vessel.
• The reaction vessel cover must form a seal with the reaction vessel and must not show any cracks.
• The reusable accessories must be cleaned thoroughly. Furthermore, the reaction vessel cover and connection tubing must be heated in the oven. See Cleaning after the determination.

The auxiliary electrode can be immersed for a few seconds in concentrated nitric acid to oxidize an accidentally applied metal coating. If after another measurement foreign metal should be found on the surface again, then the method parameters and electrode connectors need to be checked.

• ISO 182 part 3 «Tendency of PVC to evolve HCl at elevated temperatures – Part 3: Conductometric method»
• DIN 53381 «Thermostability of PVC (dehydrochlorination method)»

Possible cause: fault in the electrode setup

1. Check whether the electrode is connected to the correct measuring input and that the electrode is properly assigned in the titration method.
2. Check whether the sensor and/or measuring interface is functioning correctly – for example, by calibrating the sensor or titrating a standard substance.

Possible cause: fault in the dosing system

1. Check all tubing connections for leaks.
2. Check the buret tip for any signs of blockage.
3. Check the system for air bubbles in the dosing cylinder and/or in the tubing connections.

Other causes

1. Check whether the electrode type in use is suitable for the application.

The best thing is to create a RAM-Init. on the KF Coulometer.
If this is not possible, then you should reset all process-related settings (under Config) to the default values (Autostart off, Silo off, Start Delay off, all Monitoring to off).

No, "Eluent Dosinos" as well as "Suppressor Dosinos" in a particular method can only be used for eluent preparation or suppression, respectively. If the same Dosino is used in another method, its task can be freely defined again in the method.

For the following devices (with mainboard series 16 to 21) updating of firmware using tiamo 2.x is not possible:

• 814 with firmware up to and including 5.814.0023
• 815 and 864 with firmware up to and including 5.815.0024
• 855 with firmware up to and including 5.855.0012

tiamo 1.x and FlashBurn (devices updated with FlashBurn) are not affected. The following firmware versions take the error into consideration, i.e., as from this version updating of firmware is again possible:

• 814 from version 5.814.0024
• 815 and 864 from version 5.815.0025
• 855 from version 5.855.0013

With tiamo 2.3, however, this problem has largely been rectified.

It is advisable to condition the electrodes at least once a day before you start work.

Yes. In this case, the sample needle must be connected to the two systems via T-piece or both injectors must be installed in series.

First case: If a determination is started on the first system, the sampler is reserved for this system and the other system cannot access it. As soon as the sampler has completed its tasks, it can be released via the "Time program command" "Release". It can now be accessed by the second system. In this case too, the sampler is released after it has completed all its steps and is now available for the next request from one of the two systems. In cases of two injectors connected in series, each of the sample loops can be filled simultaneously or independently of one another.

The error is occurring because effective copying is failing.

• In the determination directory, there is a file or a directory with the same name as the intended name for the restored database.
• A directory with the name of the restored database could not be set up. (The BackupServer is possibly not started as a result of insufficient rights of the user logged onto the server.)

This is to do with the inherited rights of Windows. Windows automatically puts into the %PROGRAMFILES% directory (e.g., C:\Programs) the group CREATOR-OWNER with the relevant rights. If a new subdirectory is now set up the logged on user will automatically be entered with the rights defined for the above-mentioned group. If you don’t like this, then remove the CREATOR OWNER group. In pre-existent directories the user logged on during the setup of the directory must also be removed.

Auxiliary, reference, and working electrodes should be stored in distilled water. Storage in VMS is not recommended. If the measuring system is not used for an extended period (>24 h), then the reference electrode should be stored separately in c(KCl) = 3 mol/L. The other electrodes can also be stored dry.

No, the platinum electrode tip may not be treated in an ultrasonic bath. This will irreversibly damage the electrode.

• Use of so-called K-reagents with samples that contain ketones and aldehydes.
• Methanol-free reagents when the sample reacts with the methanol of the reagent.
• When the sample causes a pH shift to the acid range, buffering can be accomplished with solvent and imadazole.
• When the sample causes a pH shift to the alkali range, adding approx. 5 g salicylic acid or benzoic acid to the working medium helps to adjust the optimum pH range for the KF reaction.
• To suppress the side reaction, peroxides can be titrated under cold conditions, e.g., at –20 °C to –60 °C (set Ipol to 5 µA).
• If the sample (e.g., motor oil) contains various substances that react directly with the KF reagent, then a KF oven will be of help.

You will find more detailed information as to which procedure is suitable for which sample in the Metrohm KF monograph.

The "Time program" in the "Method" consists of at least one "Main program". This defines the chronological sequence of the analysis run (sampler commands, injection, start of data acquisition, etc.). Subprograms can be inserted to prevent the "Time program" becoming too complex or to allow functions that are independent of the sample.

The subprograms can be linked to "Conditions" that are used to decide whether they are to be started or skipped. For example, a subprogram can be created that is only executed for determinations used for calibrating the method.

For regulatory reasons, registered users cannot be deleted. An administrator can set the user to "inactive" (no access permission) or to "removed".

Users with a "removed" status are shifted from the original group into the "Removed users" group and no longer have access permission.

The solutions used are pipetted manually: The solution can be added with 800 Dosinos with dosing units to obtain reproducible results.

The solutions are not added through the pipette opening: During a measurement the solutions should only be added through the pipette opening.

Leading reagent manufacturers offer certified water standards for titer determination. We recommend the use of certified standards. They are simpler to handle, because larger sample volumes can be added here than with titer determination using distilled water.

Standard solutions can be obtained with the water contents 10.0 ±0.1 mg/g and 5 ±0.2 mg/mL, although the latter is not certified.

The possibility also exists of carrying out the titer determination with distilled water or with disodium tartrate dihydrate.

A. The reference electrode needs to be maintained. See also Reference electrode.

B. The baseline has not been set correctly. The baseline needs to be defined identically for each addition.

The reaction vessels and air tubes are disposable and should not be cleaned and reused. This is because:

• Removing sample residue is extremely time-consuming and therefore costly.
• Cleaning procedures that are typically applied damage the glass. The altered glass surface impairs the reproducibility and accuracy of the results.
• Poorly cleaned reaction vessels lead to scattered and, in some cases, even incorrect results.

The measuring head is not correctly locked in place on the measuring head arm: Allow the measuring head to snap into place; you need to hear it click.

The sealing rings have aged or are defective: Please contact us.

If the sample cannot be weighted directly into the reaction vessel, it must be melted carefully in the water bath beforehand.

The temperature of the water bath should only be slightly above the melting point of the sample. If the sample is heated too much, it may change in ways that could affect the end result. The sample amount corresponds to the amount that is also used for liquid samples.

The Metrohm CO2 Suppressor (MCS) requires CO2-free air. This means that the aspirated ambient air has to be precleaned using a CO2 adsorption cartridge. The CO2 adsorption cartridge must be replaced when approx. three quarters of the material has turned a violet color or at least once per year.

CVS measurements are temperature-dependent. Strong temperature fluctuations (+/- 4 °C) should be avoided to get reliable analysis results.

The CVS measuring instrument used should not be near the air outlet.

During the measurement, the temperature of the measuring solution should be kept constant. If a warm or hot bath sample is transferred into the measuring vessel, then the temperature should be adjusted. If necessary, it is possible to work with a measuring vessel with thermostat jacket (see image) and an external thermostat/cryostat. For more information, download our technical poster.

8.000.6027        Temperature dependence of CVS determinations (technical poster)

With manual evaluation, the EP is set in the corresponding coordinates selected (in this example the y1 axis represents ERC and the x axis represents volume). In the graph view of the determination, this EP is only visible if ERC has been selected as the y1 axis and volume as the x axis. Because the reading is usually selected as the y1 axis, the manually set EP «disappears» (is not displayed).

As a general rule, the auxiliary electrode is maintenance-free and does not require any special cleaning. If you want to mechanically clean the platinum pin, then you can also polish the surface. Make sure that you do not rotate the platinum pin while doing so because otherwise the internal contact may break.

Databases can be manually backed up under "Database manager". This can also be used to restore a backup copy of a database.

Every database can also be backed up automatically. This setting is in "Database manager" under "Properties" of the respective database.

To protect the column against foreign particles that could affect the separating efficiency, we recommend microfiltration of the eluents (0.45 µm filter) and aspiration through the aspiration filter.

Contaminants caused by abraded particles from the piston seals of the high-pressure pump can be avoided by fitting an Inline Filter between the pump and the injection valve.

You can use easily replaceable guard columns to protect the actual separation column and greatly extend its service life.

Samples must be free of particles before they are injected. We recommend filtering all sample solutions through a 0.45 µm filter. Furthermore, Metrohm Inline Ultrafiltration or Dialysis can also protect the column against unwanted components in the sample.

To ensure that MagIC Net operates reliably, all energy-saving functions must be switched off.

Find more information in our Software Center.

The client ID can be changed via Setup Routine and [Modify].

You can find video sequences and more information to assist you with the maintenance and care of your Metrohm IC system here:

Product Help: IC Maintenance

In exceptional cases, the evaluation algorithm cannot calculate results with the "Nonlinear regression technique" curve type. You should be able to solve the problem by selecting the "Linear Interpolation" curve type.

MISP method to remove the unwanted cationic matrix from the sample.

The sample is injected into a stream of transfer solution (generally ultrapure water). In the sample preparation module, the cations are removed from the sample and replaced by H+, Na+, or other non-critical cations (same reaction as in suppression). The analyte ions are retained by the preconcentration column and then injected for analysis.

Typical applications: Removal of heavy metals from galvanic samples.

All connections between the injector, column, and detector must be as short as possible and absolutely leak-proof. Furthermore, they should have the smallest possible dead volume. We recommend PEEK capillaries with an inner diameter of 0.25 mm for these connections. The PEEK capillary downstream of the detector block must not have any constrictions (the measuring cell is designed for a backpressure of up to 5 MPa = 50 bar). In order to ensure an optimum backpressure, it must not be shortened.

At room temperature (approx. 20 °C) and normal pressure (approx. 1000 hPa), mercury metal is liquid. The toxicity depends on the chemical and physical state of the mercury. Metallic liquid mercury is used in polarography/voltammetry.

Metallic liquid mercury

Metallic liquid mercury is relatively harmless. «If mercury is swallowed most of it passes through your body and very little is absorbed. If you touch mercury for a short period of time a small amount may pass through your skin, but not enough to harm you.» [1]. However, the problem is that metallic mercury evaporates at room temperature at a rate of 0.056 mg/(h·cm2) [2]. By comparison, the evaporation rate for water is 10 mg/(h·cm2) at room temperature [3]. Mercury vapors are absorbed through the lungs very easily and can cause both acute and chronic poisoning. For this reason, mercury should never be stored in the open and, if any drops are spilled, they must be collected immediately.

Mercury(I) salts

The sparingly soluble, inorganic mercury(I) compounds have low toxicity when taken up orally (but not through the skin!).

Mercury(II) salts

Mercury(II) compounds are more readily soluble and therefore much more toxic. Toxicity to fish: LC50 – Oncorhynchus mykiss (rainbow trout) – 0.016 mg/L – 96 h [4].

Mercury vapors

Mercury vapor, which is already formed at room temperature, is highly toxic: vapor with a mercury concentration exceeding the TLV (threshold limit value) or OEL (occupational exposure limit value) causes chronic poisoning after prolonged breathing for 5 to 8 hours per day. The limit values vary depending on the country and range between 20 and 100 µg/m3 of air [5][6][7][8]. Despite the large number of laboratories involved in polarographic/voltammetric work, sensible and proper handling has ensured that not one single case of mercury poisoning has been reported to date. The real Hg concentrations measured in the laboratory atmosphere are consistently far below the TLV.

Organic mercury compounds

Organic mercury compounds are very toxic. Dimethylmercury is an extremely toxic form of organic mercury, and very small exposures can cause severe and irreversible delayed neurotoxicity, including death. Dimethylmercury is thought to be metabolized to methylmercury prior to crossing the blood-brain barrier. Dimethylmercury is quickly absorbed through intact skin, and it will penetrate latex or polyvinyl gloves. It is highly volatile, will readily evaporate, and can be inhaled [9].

 

[1] Mercury Quick Facts – Health Effects of Mercury Exposure, Agency for Toxic Substances and Disease Registry, www.atsdr.cdc.gov/mercury/docs/healtheffectsmercury.pdf

[2] United Nations Environment Programme (UNEP), Code of Practice Mercury Housekeeping, https://www.unep.org/resources/report/code-practice-mercury-housekeeping

[3] F. Asdrubali, A scale model to evaluate water evaporation from indoor swimming pools, Energy and Buildings, 41 (2009), 311–319

[4] Material safety data sheet for mercury(II) chloride, https://www.merckmillipore.com/CH/de/product/msds/MDA_CHEM-104419

[5] Occupational Safety and Health Administration standards related to mercury, https://www.osha.gov/mercury/standards

[6] Technische Regeln für Gefahrstoffe 900 – Arbeitsplatzgrenzwerte http://www.baua.de/de/Themen-von-A-Z/Gefahrstoffe/TRGS/TRGS-900.html

[7] Bundesamt für Gesundheit – Quecksilber – Factsheet Quecksilber, https://www.bag.admin.ch/dam/bag/de/dokumente/chem/themen-a-z/factsheet-quecksilber.pdf.download.pdf/factsheet-quecksilber_de.pdf

[8] European Commission, Brussels, BiPRO 16 April 2010, Requirements for facilities and acceptance criteria for the disposal of metallic mercury, http://ec.europa.eu/environment/chemicals/mercury/pdf/bipro_study20100416.pdf

[9] John Risher, Ph.D., Rob DeWoskin, Ph.D. 1999, Agency for toxic substances & disease registry. Toxicological Profile for Mercury. 1999. http://www.atsdr.cdc.gov/toxprofiles/tp46.pdf

If the drift during pretitration (conditioning) is too high after the addition of fresh working medium, then this is a sign that the titration cell is not protected sufficiently against humidity. Replace the molecular sieve and the septum, also check whether all of the O-rings/PTFE sleeves are in proper working condition (damage, cracking).

If the drift is too high after the completion of a sample titration, then this is usually because of other reasons:

• The sample has not dissolved completely during titration and continues to release water. An increase of the extraction time or other sample pretreatment steps are recommended. Read for more details in the following FAQ: «What to do to improve the release of water?»
• The sample reacts with the KF reagent, a side reaction takes place. Depending on the type of the side reaction, this can be suppressed not only with special reagents, but also by means of appropriate titration methods (KF oven method, titration in the cold, or external extraction).
• The sample has shifted the pH value. Read for more details in the following FAQ: «How can I prevent side reactions or pH value shifts?»

Undersized peak areas often indicate that the sample quantity is too small.

• There is a leak in the sample path: Check the sample path.

• The sample path is blocked: Check whether the sample is flowing during filling of the sample loop. If the sample flow rate is too low or zero, check the settings and then look for the blockage in the sample path and remove it.

• The sample loop is not completely filled: Adjust the transfer time.

• There are gas bubbles in the sample: Use the sample degasser.

• The MCS (CO2 suppressor) is not connected: Connect the MCS and check the CO2 cartridge.

• The high-pressure pump has contaminated valves: Clean or replace the pump valves.

• The high-pressure pump has defective piston seals: Replace the piston seals and, if necessary, the pistons.

In cases of samples with low solubility, one of the following procedures is recommended:

A) Use of a solubility promoter

Volumetric KF titration

Solvent	Percentage	Samples
Formamide	max. 50%	Sugar samples, salts
Chloroform	max. 70%	Oil, grease
Long-chain alcohols	max. 50%	Oil, grease
Xylene, toluene	max. 70%	Crude oils with tars

Coulometric KF titration

Solvent	Percentage	Samples
Formamide*	max. 20%	Sugar samples, salts
Chloroform**	max. 30%	Oil, grease
Long-chain alcohols**	max. 30%	Oil, grease
Xylene, toluene**	max. 30%	Crude oils with tars

* Only with generator electrode without diaphragm.
** Use generator electrode with diaphragm if the amount of solubility promoter is higher than 10%.

B) Titration at a higher temperature

Temperature	Samples
40 °C / 50 °C	Vegetable samples, salts, fat-containing samples, food samples

C) Mechanical pretreatment

• Homogenizer
• Mortar
• Lab mill (cooled)

These procedures can also be combined with each other. Detailed information as to which procedure is suitable for which sample can be found in the Metrohm KF monograph.

Select the determinations of these standards in the "Database" as well as all determinations of samples that are to be recalculated.

In the "Determinations" menu, select "Reprocessing…" or click the corresponding icon.

Select one of the standards in the "Reprocessing table" and correct the entries in the component table. Clicking "Update" applies the changed parameters to the selected determination. The peaks in the chromatogram are now correctly labeled.

Select "Reprocessing" and then the option "From the standards of the reprocessing table". All the determinations are recalculated using the parameters of the selected line.

If the result of the reprocessing is satisfactory, save the reprocessed determinations by closing the reprocessing window with "OK".

The reference potential is offset: Perform maintenance for the reference electrode in accordance with the electrode data sheet.

There are three types of subprograms:

1. "Sequence": The commands of the "Subprogram" are processed first before proceeding with the next line in the "Main program".
2. "Loop": Analogous to Sequence, but the commands of the "Subprogram" are executed consecutively n times. The number of runs can be fixed or defined at the start of the loop by means of a formula.
3. "Parallel": This "Subprogram" runs parallel to the "Main program" or to the respective "Subprogram".

Yes. tiamo runs in a protected Java environment. If possible, the requirements in the installation instructions should be met.

Select the determinations of these standards in the database.

In the "Determinations" menu, select "Reprocessing…" or click the corresponding icon.

Select the standard with the required calibration; this is generally the last determination.

To reprocess, select the option "Of the marked determination".

If the result of the reprocessing is satisfactory, save the reprocessed determinations by closing the reprocessing window with "OK".

The procedure for further problems during "Reprocessing" is described in the online help under "How to proceed?".

This can happen if the two PCs do not have the same time zone and summer time / winter time settings. The precise global time is displayed. If it is 12 noon in Bern, then it is 6 a.m. in New York.

This should not actually be the case, but if this situation does occur there are very differing reasons.

The tiamo database path should be defined as an exception in the virus scanner, so that this path is not scanned. Furthermore, no backups should be created when you want to use the system.

The more databases there are, the longer it will take to open the «Open database» dialog or the database manager. The reason is that all databases first have to be opened and all the information (e.g., size) has to be read out before everything is displayed.

Use of powerful hardware, e.g., a RAID-5 system, is always recommended.

A different reference electrode yields a different reference potential and therefore a different zero-point on the potential axis. Method parameters are always given relative to the reference potential. To be able to measure using the Ag/AgCl reference electrode, you just need to adjust all potentials by the potential difference between the reference electrode described and the Ag/AgCl reference electrode.

The table shows the potentials of some common reference electrodes measured against a standard hydrogen electrode.

Reference electrode	Potential compared to SHE (standard hydrogen electrode at 25 °C)
Ag/AgCl, c(KCl) = 3 mol/L	+207 mV
Ag/AgCl, c(KCl) = 1 mol/L	+236 mV
Hg/Hg2Cl2, c(KCl) = sat. (SCE – saturated calomel electrode)	+241 mV
Hg/Hg2Cl2, c(KCl) = 1 mol/L (NCE – normal calomel electrode)	+280 mV
Ag/AgCl, c(KCl) = 0.1 mol/L	+291 mV

The figure shows the signal “shift” resulting from different reference potentials. 

The dosing units used should be disassembled and thoroughly cleaned at 14-day intervals.

During the installation of clients the network is checked for functionality. This includes testing of the backup server. However, the backup server only runs if you are logged onto the server in Windows. You thus have to be logged onto the server to facilitate testing of the backup servers.

There are time program commands available with which drift, noise, and the current measured value of a detector can be determined.

These commands can be inserted at the appropriate place in the "Time program". You need to create a new line in the "Time program" for this. The corresponding commands are given under the respective detector. A comment can be entered for a measured detector value. Drift and noise also require definition of a certain measuring period. To obtain correct values for drift and noise, it must be ensured that no changes to the baseline occur during the respective measuring period.

Rinse the tubing using the Preparation/«Prep» command before the first measurement if the system has not been used overnight or for even longer periods.

The titrant can change over time in the plastic tubing, which will falsify your results. In addition, the «Prep» procedure removes any air bubbles that may be present in the tubing.

There should be at least enough sample in the reaction vessel so that the air tube is still submerged in the sample at the end of the measurement. That is the case for a volume of approximately 2 mL and above.

There should only be as much sample in the reaction vessel so that the entire sample fits in the heated section of the heating block. That is the case for a volume of up to approximately 12 mL.
In most applications, between 3 and 7.5 g of the sample are used.

• Gas bubbles in the eluent: Degas the eluent and check the connectors of the eluent degasser.

• The injector is defective: Check the installation of the sample loop. If the injector is defective, please contact Metrohm Service.

• The sample loop is not completely filled: The transfer and rinsing times must be adjusted.

• The vacuum in the MCS (CO2 suppressor) is insufficient: Check the connectors. If these are OK, please contact Metrohm Service.

MISP method for sample neutralization.

The sample is injected into a stream of transfer solution (generally ultrapure water). The sample is neutralized in the sample preparation module (same reaction as for suppression). The analyte ions are retained by the preconcentration column and then injected for analysis.

Typical applications: trace analysis of anions in NaOH solutions.

No. In accordance with FDA requirements, this list always contains all currently registered clients.

A "Timer" is available in MagIC Net. This can be used to define single or recurrent "Tasks" that are to be started at a certain time or date/time.

The available "Actions" are: "Start equilibration", "Start sample table", and "Stop devices". This can be used, e.g., to start the IC system early enough in the morning so that the system is already equilibrated when work is started.

No chloride is contained in the VMS: Check the preparation of the VMS and modify if necessary.

MIDT can be used to automatically dilute the sample according to a preset dilution factor.

A Dosino is used for handling the liquids. In addition to automatic calibration using one standard solution, logical dilutions can also be carried out. This means that MagIC Net checks whether all the results lie within the calibration range. If this requirement is not met, dilution is triggered once again, followed by injection with an adjusted dilution factor.

For logistical and technical reasons, Metrohm cannot offer a polishing service for used platinum electrode tips.

The 800 Dosino is a universal tool for Liquid Handling. It can be used not only for simple transfer of solutions, but also for dosing quantities with a µL accuracy. Typical applications include sample transfer, MSM regeneration, rinsing, eluent preparation, Dose-in Gradient, and accurate sample dosing for sample preparation techniques such as MiPT, MiPCT, MIDT, etc.

If a method is reloaded, the statistics series will be reset. A method is also reloaded if you reload the same method, even though it is the same method. The method is also reloaded if you switch from the Single Determination tab to the Determination Series tab or vice versa.

The sample has been contaminated before the sample was injected. Check the sampling procedure and the cleanliness of the sample vessels.
Carry-over from the previous sample has occurred. Increase the rinsing and transfer times.