Why is sample preparation prior to separation essential for your analysis?

When using ion chromatography (IC) as an analytical technique, samples often cannot be injected directly onto the separation column. There are several reasons for this: samples may contain particles or colloids, the analyte concentration can be too high or low, the sample matrix is unsuitable for a direct injection, or the sample first requires neutralization. These are common and sometimes elaborate challenges faced in daily laboratory work. Metrohm Inline Sample Preparation (MISP) techniques offer a broad spectrum of straightforward, cost- and time-saving solutions for these kinds of situations. This article gives an overview and some insights about MISP techniques—our solutions for automated inline sample preparation of various matrices for IC analysis. Using MISP is the first step to saving valuable time and money while increasing the reliability and precision of your measurements.

Metrohm offers dosing units in different volumes (2, 5, 10, 20, and 50 mL) to suit the liquid handling requirements of nearly any laboratory application.
Figure 1. Metrohm offers dosing units in different volumes (2, 5, 10, 20, and 50 mL) to suit the liquid handling requirements of nearly any laboratory application.

Introduction to MISP

If you look closely at the «MISP» acronym i.e., Metrohm Inline Sample Preparation, you should have identified the term «inline» – the automated way of sample preparation incorporated in Metrohm IC systems. The underlying concept is that the only manual action analysts have with a sample is when they place it on the autosampler. The specific steps for sample preparation will be automatically handled «inline» by the system from that moment on. High reproducibility of the completely automated sample preparation excludes any manual interferences (e.g., unidentical handling, bias, or other errors introduced during manual sample preparation) which could lead to irreproducible results. Automated sequences have been proven without a doubt to significantly increase the precision and reliability of analytical results. Furthermore, with an absolute minimum of manual labor, lab analysts can save both time and money by letting the IC system do the hard work.

Metrohm has the perfect tool in hand for high precision, accurate liquid handling: our patented Dosino (Figure 1). The Dosino technology ensures that volumes down to single digit µL can be measured out and transferred quickly and precisely. 

All steps related to the inline sample preparation process occur in between the autosampler, on which the samples are placed, and the injection of the sample onto the analytical column with the 6-port valve (Figure 2). 

Figure 2. Illustrated IC sample path flowchart with possible Metrohm Inline and automated Sample Preparation and Injection techniques noted.

The most common Inline Sample Preparation solutions from Metrohm: Ultrafiltration, Dialysis, Dilution, and Partial Loop Injection

Many kinds of samples contain particles (e.g., wastewater, river water, etc.), and these should never be injected directly onto the separation column. For this reason, Metrohm offers IC instruments with an ultrafiltration solution in which the particles are removed from the sample prior to injection. Inline Ultrafiltration is fully automated and does not require any manual sample filtering, saving time and effort in addition to the consumable costs of e.g., individual filters.

Click on the video to see how the Inline Ultrafiltration principle works.

An economical solution that can easily remove colloids, proteins, or oil droplets from high organic load sample matrices is Inline Dialysis. In contrast to traditional Carrez precipitation, numerous manual steps are omitted, making Inline Dialysis an economical and straightforward technique to analyze complex samples such as fruit and vegetable juices, milk, or other dairy products. Both Inline Ultrafiltration and Dialysis guarantee the longest separation column lifetimes and protect IC systems against unnecessary downtime.

The Partial Loop Injection technique (MiPT) or Inline Dilution can be added to the Ultrafiltration setup when the sample concentration range is outside of the calibration range. Another significant advantage of using MiPT or Inline Dilution is the possibility of performing automatic Inline Calibration out of only one stock standard solution. This again saves valuable time that would otherwise be spent on standard series preparation, and additionally increases data reliability by reducing pipetting and calculation errors to a minimum.

Figure 3 shows how Metrohm IC enables its low cost of ownership principles. These numbers are based on a US contract laboratory that analyzes approximately 14,000 samples per year on a Metrohm IC system. Aside from prolonging the column lifetime with Inline Ultrafiltration and adjusting the sample concentration with automated Inline Dilution, this data clearly shows a large impact on cost savings as well when applying MISP techniques to IC analysis.

Figure 3. Low cost of ownership using Metrohm Inline Sample Preparation techniques and high-quality IC equipment.

Sample matrices are extremely varied. Therefore, more specific MISP techniques are required (Figure 4) and will be explained in more detail within the following sections. 

Figure 4. Various Metrohm Inline Sample Preparation solutions matched to their specific situations.

Metrohm Inline Extraction

Extraction, a common sample cleanup and preparation step, makes it possible to transfer components from one medium into another, thereby enabling the analysis of ionic components in non-polar organic matrices. There are many different extraction procedures e.g., the classical liquid-liquid extraction. As an automated process, Metrohm Inline Extraction, a liquid-liquid process, is used to transfer water-soluble components from a non-polar organic phase (such as bioethanol) into the aqueous phase—essential for IC analysis. An exact amount of the sample (organic phase) is transferred to the dilution vessel in which the medium (usually ultrapure water) is added and stirred for a certain time period. Two phases are formed, with the aqueous phase now containing all extractable water-soluble components of the original sample. Any organic droplets remaining are removed from this phase during subsequent automated Metrohm Inline Dialysis.

Metrohm Inline Preconcentration

For each analytical method, there are limits regarding the smallest detectable concentration. With ion chromatography, depending on the system used, these limits are between 0.1 µg/L and 100 µg/L for a full loop injection of 20 µL. Metrohm Inline Preconcentration increases measuring sensitivity considerably and opens up accurate measurements in concentration ranges down to the ng/L range.

For this MISP technique, a preconcentration column (PCC) is used instead of a sample loop. This column features functional properties very similar to those of separation columns—if a defined volume of sample is passed over the PCC, the relevant ions are retained. Through injection, the accumulated ions are eluted with the eluent onto the separation column.

Click on the video to see how Metrohm Inline Preconcentration works.

Intelligent Preconcentration with Inline Matrix Elimination

The Metrohm intelligent Preconcentration Technique with Matrix Elimination (MiPCT-ME) allows low concentrations of analytes present in a non-ionic matrix to be determined with a high degree of reproducibility. Once the sample is flushed through a preconcentration column, the non-ionic components of the sample are rinsed off of the preconcentration column with ultrapure water.

Removing the non-ionic components from the sample prevents them from interfering with the target analytes. Analyte concentrations can be measured in the ng/L to mg/L range with a high degree of precision and accuracy using MiPCT-ME (Figure 5). This automated inline sample preparation technique is used in general for trace analysis in matrices such as methanol, hydrogen peroxide, isopropanol, ethanol, power plant water samples, and semiconductor grade chemicals.

Figure 5. Chromatogram of a brine sample (>300 g/L NaCl) spiked with 60 µg/L strontium and barium. An aliquot of 4 mL sample was preconcentrated on the Metrosep Chel PCC 1 VHC/4.0 allowing very low detection limits (10 μg/L) and then eluted on a Metrosep C6 - 150/4.0 separation column.

Metrohm Inline Neutralization

Strongly alkaline or acidic samples can result in problems for ion chromatographic analysis as they can cause damages to the separation column and create a direct impact on the separation efficiency. These kinds of samples may naturally be acidic or alkaline, or could be due to digestion processes necessary to extract analytes from soils, textiles, or other solid matrices. With the help of Metrohm Inline Neutralization, such samples can be prepared fully automatically during sample injection and then analyzed directly without any manual intervention. This technique is also suitable for determining ultratrace analytes. After Inline Neutralization, even strongly alkaline samples can be preconcentrated, thus facilitating analyses in the ng/L concentration range.

Metrohm Inline Cation Removal

Metrohm Inline Cation Removal is an especially handy tool used to remove transition metals from electroplating samples, for example. The metal ions are exchanged for sodium (Na+) in the Sample Preparation Module. A simple exchange for protons is sometimes unsuitable, specifically for samples from the electroplating industry, since this would render the sample too acidic. Inline Cation Removal prevents any precipitation of metal hydroxides in the IC system. Analysis with integrated Inline Cation Removal functions fully automatically, robustly, and reliably.

Summary

MISP techniques offer laboratories many solutions for their manual sample preparation challenges. The results are clear:

  • less time is spent on tedious, repetitive tasks
  • data is more reliable and reproducible when manual errors are minimized
  • cost savings via reduced manual labor and faster sample throughput


More highlights for Metrohm Inline Sample Preparation are listed in the table below. 

MISP Highlights

Unique, partially patented and fully automated sample preparation
Inline transfer of a solid, liquid, or gaseous sample through to injection
Improves precision and accuracy of the analysis results
Minimizes processing time
Reduces manual steps
Guarantees traceability for each sample preparation step
Minimizes the risk of contamination
Opens up new application areas
Self-optimizing analyses based on logical decisions of the system
Professional liquid handling thanks to Dosino technology

Depending on the application, Metrohm offers a variety of ProfIC Vario systems consisting of automated MISP techniques combined with a fully equipped 940 Professional IC Vario including automation. 

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Brad Meadows is Vice President and Lab Director at the US company BSK Labs, which runs a number of environmental laboratories and service centers. Brad is an analytical chemist and has been working in the management of analysis laboratories for 15 years. He shared his experiences with Metrohm ion chromatography with us in the form of some concrete facts and figures.

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Jonas Loof

Sr. Product Specialist Ion Chromatography (Automation and sample preparation)
Metrohm International Headquarters, Herisau, Switzerland

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