Applications

The coupling of highly efficient ion chromatography (IC) to multi-dimensional detectors such as a mass spectrometer (MS) or an inductively coupled plasma mass spectrometer (ICP/MS) significantly increases sensitivity while simultaneously reducing possible matrix interference to the absolute minimum. By means of IC/MS several oxyhalides such as bromate and perchlorate can be detected in the sub-ppb range. Additionally, organic acids can be precisely quantified through mass-based determination even in the presence of high salt matrices. By means of IC-ICP/MS different valence states of the potentially hazardous chromium, arsenic and selenium in the form of inorganic and organic species can be sensitively and unambiguously identified in one single run.

UV/VIS detection is one of the most sensitive detection techniques in trace-level chromatography. Sometimes, however, spectrophotometric detection lacks sensitivity, selectivity or reproducibility and chemical derivatizations are required. By using Metrohm`s rugged and versatile flow-through reactor, single- or multi-step derivatizations can be done fully automatically, in either pre- or post-column mode at any temperature between 25…120 °C. The variable reactor geometry allows to adjust the reactor residence time of the reactants according to derivatization kinetics. The flexibility of the reactor is demonstrated by optimizing four widespread post-column techniques: the relatively slow ninhydrin reaction with amino acids and the fast derivatizations of silicate, bromate and chromate(VI).

Because of its toxicity, the World Health Organization recommends a maximum arsenic content in drinking water of 10 μg/L. Anodic stripping voltammetry with the scTRACE Gold offers a straightforward, highly affordable alternative to spectroscopic determination.

An automatic titration method is described using biamperometric endpoint indication for the determination of antimony in antimony-alloyed cable lead (approx. 1% Sb). A 0.01 mol/L KBrO3 solution is used as the titrant.

In the following tables, the half-wave potentials or peak potentials of 90 metal ions are listed. The half-wave potentials (listed in volts) are measured at the dropping mercury electrode (DME) at 25 °C unless indicated otherwise.

Boric acid is used in many primary circuits of nuclear power plants, in nickel plating baths, and in the production of optical glasses. Furthermore, boron compounds are found in washing powders and fertilizers. This bulletin describes the potentiometric and thermometric determination of boric acid. The determination also covers further boron compounds, when acidic digestion is applied.

This Application Bulletin describes the voltammetric determination of the elements antimony, bismuth, and copper. The limit of detection for the three elements is 0.5 ... 1 µg/L.

In the past, selenium determinations have always been either unreliable or have required complicated methods. However, as selenium is on the one hand an essential trace element (vegetable and animal tissues contain about 10 μg/kg), while on the other hand it is very toxic (threshold value 0.1 mg/m3), it is very important to cover determinations in the micro range. Cathodic stripping voltammetry (CSV) enables selenium to be determined in mass concentrations down to ρ(Se(IV)) = 0.3 μg/L.

This Bulletin gives a survey of standard methods from the field of water analysis. You will also find the analytical instruments required for the respective determinations and references to the corresponding Metrohm Application Bulletins and Application Notes. The following parameters are dealt with: electrical conductivity, pH value, fluoride, ammonium and Kjeldahl nitrogen, anions and cations by means of ion chromatography, heavy metals by means of voltammetry, chemical oxygen demand (COD), water hardness, free chlorine as well as a few other water constituents.

This Bulletin describes the determination of arsenic by anodic stripping voltammetry (ASV) at the rotating gold electrode. A determination limit of 0.5 μg/L can be achieved with 10 mL sample solution. A differentiation between the As(III) concentration and the total arsenic concentration can be made by appropriate selection of the deposition potential. The analyses are performed with a special gold electrode whose active surface is located laterally; c(HCl) = 5 mol/L is used as supporting electrolyte. For the determination of the total arsenic content, As(III) and As(V) are reduced at -1200 mV by nascent hydrogen to As0, which is preconcentrated on the electrode surface. If the deposition is carried out at -200 mV then only As(III) is reduced; this allows the differentiation between total arsenic and As(III). During the subsequent voltammetric determination the preconcentrated As0 is again oxidized to As(III).

This bulletin deals with the automated determination of mixtures of HNO3, HF and H2SiF6 in the range of approximately 200-600 g/L HNO3, 50-160 g/L HF, and 0-185 g/L H2SiF6 using thermometric titration.Etch acid mixtures containing HNO3, HF and H2SiF6 from the etching of silicon substrates can be analyzed in a sequence of two determinations using the 859 Titrotherm. The first determination involves a direct titration with standard c(NaOH) = 2 mol/L, followed by a back titration with c(HCl) = 2 mol/L. This determination yields the H2SiF6 content plus a value for the combined (HNO3+HF) contents. The second determination consists of a titration with c(Al3+) = 0.5 mol/L to determine the HF content. For freshly made up mixtures of HNO3 and HF containing no H2SiF6, a linked two-titration sequence is employed. Results from the two determinations are used by tiamoTM to yield individual results for HNO3, HF and H2SiF6.

This Application Bulletin describes the determination of arsenic in water samples by anodic stripping voltammetry using the scTRACE Gold sensor. This method makes it possible to distinguish between As(total) and As(III). With a deposition time of 60 s, the limit of detection for As(total) is 0.9 µg/L, for As(III) it is 0.3 µg/L.

Determination of sodium, potassium, and silica values in sodium and potassium silicates.

Automated determination of the H2SiF6 and HF contents of industrial grade hexafluorosilicic acid.

Determination of boron in ores of the element such as borax and ulexite.

Following the addition of caustic soda, hexafluorosilic acid can be determined through back titration of excess hydroxide with hydrochloric acid. Hydrofluoric acid (hydrogen fluoride) is determined by precipitation with aluminum in the presence of sodium and potassium ions. Nitric acid is determined by subtracting the equivalence concentrations of hexafluorosilic acid and hydrofluoric acid from the total acid concentration.

The maximum contaminant concentrations (Maximal Contaminant Level, MCL) of inorganic arsenic and selenium species in drinking water should not exceed 10 and 50 µg/L, respectively. Given that each of the two elements occurs in two oxidation levels – trivalent and pentavalent – a separation step is necessary prior to ICP/MS detection. This Application Note shows the simultaneous determination of the two arsenic (arsenite and arsenate) and selenium species (selenite and selenate). Separation takes place on the Metrosep Dual 3 - 100/4.0 column.

Determination of silica (as silicate) in pure water with preconcentration using anion chromatography with direct conductivity detection (without any post-column reaction).

Determination of silicate in tap water using anion chromatography with direct conductivity detection.

Determination of borate and silicate in washing powder using anion chromatography with direct conductivity detection.

Determination of borate and silicate in ultrapure water using anion chromatography with direct conductivity detection.

Determination of silicate and borate and their limits of determination (LOD) and quantification (LOQ) according to the EPA procedure for method detection limit (MDL) using anion chromatography with direct conductivity detection and Metrohm Inline Calibration.

Determination of borate in a borate effluent using anion chromatography with direct conductivity detection.

Determination of borate in seawater using ion-exclusion chromatography with suppressed conductivity detection after inline matrix elimination.

The human daily intake of boron from food and beverages is approximately 2 mg. This is far below any toxic level. Some plants, however, are extremely sensitive to boron concentrations above 1 mg/L, e.g., strawberries, blackberries. As seawater contains 4 to 5.5 mg/L of boron, desalination is required to remove surplus boron besides other ions. This application shows the determination of boron (as borate) by ion-exclusion chromatography with conductivity detection after inverse suppression. The method has been optimized to get a sufficient fluoride/borate separation.

This Process Application Note is dedicated to the online analysis of zinc, iron and sulfuric acid in several stages of the zinc production process. Additionally, traces of germanium, antimony, as well as several transition metals (e.g., Ni, Co, Cu, Cd) can be precisely determined (<50 µg/L) in the purification filtrates and reactor trains.

Boric acid requires precise monitoring in the primary circuit to control nuclear reactor reactivity. The 2060 TI Process Analyzer monitors boric acid online in near-real time.

Excessive silica concentrations in the boiler feed water can lead to deposits on turbine blades and must therefore be avoided. Silica analysis is carried out via differential photometry using a leading-edge technology thermostatic cuvette module for non-sample contact at the detector. Typical concentration ranges for silica are 0–50 ppb and 0–1 ppm or higher.

Boric acid is growing in demand for various industrial applications, but requires a more cost-efficient and environmentally friendly production process. This Application Note describes the performance of a Raman process analyzer (PTRam) when measuring low-concentration boric acid and sodium sulfate solutions (<100 mg/L) during boric acid production.

Determination of borate and chloride with direct conductivity detection (exhausted MSM). After the introduction of the fresh MSM unit and after the eluent change, sulfate is analyzed with conductivity detection after chemical suppression.

Determination of silicate, sulfate, and phosphate in a clay extract using anion chromatography with conductivity detection before and after chemical suppression. Using a step gradient and switching valve to work with or without chemical suppression.

Determination of arsenite, arsenate, selenite, selenate, chloride, and sulfate using anion chromatography with a combination of suppressed and non-suppressed conductivity detection.

Determination of 21 anions and organic acids using anion chromatography with conductivity detection after chemical suppression and applying a high pressure gradient.

Determination of fluoride, chloride, nitrite, selenite, phosphate, nitrate, sulfate, and selenate using anion chromatography with conductivity detection after chemical suppression.

Determination of fluoride, hypophosphite, chlorite, bromate, chloride, nitrite, bromide, chlorate, nitrate, phosphite, phosphate, sulfate, arsenate, iodide, chromate, and perchlorate using anion chromatography with conductivity detection after gradient elution and chemical suppression.

Determination of fluoride, chloride, nitrate, phosphate, sulfate, silicate, and hexafluorosilicate (calculated) using anion chromatography with conductivity detection after chemical suppression and subsequent UV/VIS detection with post-column reaction (see AN U-48). Hexafluorosilicate is hydrolyzed into fluoride and silicate. Both anion concentrations can be used for the calculation of the SiF62- concentration.

The anion column Metrosep A Supp 15 - 150/4.0 is a pretty high-capacity column. The direct determination of arsenate in a matrix of 180 mg/L chloride and 320 mg/L sulfate is not possible, as the arsenate is hardly detectable under the sulfate peak tail. Sample reinjection cuts off the majority of the matrix and therefore allows an accurate determination of the arsenate.

Determination of arsenic in dust from a waste incineration plant is performed. This is required as the environmental risk depends on the degree of oxidation of the arsenic species. Due to the different pKa of the respective anions, selenite requires non-suppressed conductivity detection, while arsenate is best determined with suppression. The determination of both species is achieved by switching the suppressor in and out, respectively.

Determination of Na2O and SiO2 in water glass by potentiometric titration with HCl using the Sb electrode.

Determination of arsenite and arsenate in process water using ion-exclusion chromatography with UV detection.

Determination of silicate and hexafluorosilicate (calculated) using anion chromatography with conductivity detection after chemical suppression (see AN S-277) and subsequent UV/VIS detection with post-column reaction. Hexafluorosilicate is hydrolyzed into fluoride and silicate. Both anion concentrations may be used for the calculation of the SiF62- concentration.

Scale formation is a critical issue in cooling systems leading to system damage, which generates enormous operational losses. One important component of scale forming is silica. Amorphous silica and metal silicates especially tend to build up scale. Therefore, it is crucial to know the silica concentration in cooling agents. By ion chromatography with UV/VIS detection and PCR, it is possible to determine both free and total silicate content. Sample dilution in ultrapure water and direct injection delivers the free silicate concentration. The total silicate content is determined after hydrolysis of amorphous silica by sample dilution in alkaline eluent, and injection after a reaction time (e.g. 4 hours) prior to the analysis.

Determination of Cd, Pb, and Sb in acetic acid.

Determination of Ni, Sb, Cd, Tl, and Cu in a neutral, highly concentrated zinc solution from the plating industry.

Determination of Cr and Se in a silver plating bath.

Simultaneous determination of Sb and Bi in an alkaline ZnO solution.

Voltammetric determination of boron in plasma using Beryllon III as a ligand [L. Thunus (1996), Anal. Chim. Acta 318: 303–308].

The concentration of total Sb in zinc plant electrolytes is determined by anodic stripping voltammetry (ASV) in 5 mol/L HCl. If 0.6 mol/L HCl is used, only the concentration of antimony(III) is determined selectively. The interference of an excess of Cu is suppressed by the selective oxidation of Cu. Nevertheless, the concentration of Cu in the sample limits the amount of sample that can be used for the determination.

Germanium can be determined by adsorptive stripping voltammetry (AdSV) at the HMDE using acetate buffer as supporting electrolyte and catechol as complexing agent.

Germanium can be determined by adsorptive stripping voltammetry (AdSV) at the HMDE using acetate buffer as supporting electrolyte and catechol as complexing agent.

Selenium is determined by cathodic stripping voltammetry (CSV) at the hanging mercury drop electrode (HMDE). Se(IV) is deposited on the surface of the mercury drop in sulfuric acid electrolyte under addition of copper ions as Cu xSe y.Wastewater samples containing organic contaminants have to be digested by UV irradiation before analysis. In addition, the sample has to undergo a second irradiation step at pH 7−9 to reduce Se(VI) to Se(IV), since only Se(IV) is electrochemically active.

Germanium is determined by adsorptive stripping voltammetry (AdSV) at the HMDE using aqueous sulfuric acid as supporting electrolyte and pyrocatechol violet as complexing agent. It is possible to determine 20 µg/L Ge in a sample containing 150 g/L Zn, 3 g/L Cd and 1 mg/L Pb.

Sb is determined in polyethylene terephthalate (PET) after digestion in sulfuric acid and hydrogen peroxide. The application is carried out with anodic stripping voltammetry (ASV) in hydrochloric acid.

The concentration of Sb(total) in an acid Cu bath is determined by anodic stripping voltammetry using hydrochloric acid as electrolyte. Due to the excess of Cu the deposition potential has to be chosen only 50 mV more negative than the Sb signal

The concentration of Sb(III) and Sb(total) in an electroless nickel bath is determined by anodic stripping voltammetry (ASV). In c(HCl) = 0.6 mol/L only Sb(III) shows a signal. In w(HCl) = 10% the Sb(total) content is determined.

The concentration of Se(IV) in zinc plant electrolyte is determined by cathodic stripping voltammetry (CSV) in ammonium sulfate electrolyte containing EDTA and Cu. The Cu concentration has to be adapted to the sample and the deposition time. With voltammetry only free selenium is determined, therefore it has to be taken into consideration that selenium forms sparingly soluble compounds with numerous cations (e.g. Fe2(SeO3 )3 with Ks = 2·10-31).

The concentration of Te(IV) in Zn plant electrolyte is determined by cathodic stripping voltammetry (CSV) in ammonium sulfate electrolyte containing EDTA and Cu. To get a proper complexation of the interfering Zn a high amount of EDTA is necessary at pH 3.4.

The concentration of As(total) in zinc plant electrolyte is determined by anodic stripping voltammetry (ASV) on a lateral gold electrode in HCl electrolyte. Due to the high excess of zinc in the sample the deposition potential has to be adapted. A second potential approx. 100 mV more negative than the arsenic signal has to be applied to selectively oxidize interfering antimony. For sample preparation the sample was passed through a cation exchange column to reduce the concentration of zinc in the measuring solution.

The concentration of of Sb(III) in zinc plant electrolyte is determined by adsorptive stripping voltammetry (AdSV) with chloranilic acid as complexing agent. In this method high copper concentrations do not interfere. An approx. 10-fold excess of lead interferes, since it shows a signal close to the antimony. With the parameters given below the working range of this method is 1 - 30 µg/L antimony(III) with respect to the concentration in the measuring vessel.

The Se(IV) concentration can be determined by cathodic Stripping Voltammetry (CSV) in an ammonium sulfate electrolyte. The analysis also functions in the presence of Cu. Se(IV) is determined in the first step. In order to register the entire content of Se, Se(VI) species are first reduced to Se(IV). This is handled by the 909 UV Digester at a pH value of between 7 and 9. The method requires practically no reagents and permits selenium speciation.

Electroless nickel plating is an important and well established process in the surface finishing industry. In the past the addition of small amounts of lead has widely been used to stabilize the plating bath. With the increasing number of restrictions in recent years on the use of lead in consumber products, particularly electronics, alternative stabilizers were developed and introduced. Two of the stabilizers used as lead replacement are antimony and bismuth. They can be used as a single additive or in combination with each other or iodate. This method allows the determination of antimony and bismuth directly in the plating bath sample by anodic stripping voltammetry (ASV). The method is simple and fast, however sensitive and robust

This Application Note describes the polarographic determination of selenite in electroplating baths used in the production of copper indium gallium diselenide thin-film solar cells (CIGS cells). The CIGS absorber layer is electrodeposited on a molybdenum-coated substrate. Selenite analysis is carried out after dilution of the sample with sulfuric acid as supporting electrolyte.

Arsenic is ubiquitous in the earth’s crust in low concentrations. Elevated levels can be found in mineral deposits and ores. Arsenic from such deposits leaches into the groundwater in the form of arsenite (AsO33–) and arsenate (AsO43–), causing its contamination. In addition to the arsenic originating from natural sources, industry and agriculture contribute to the contamination to a lower extent. The guideline value for inorganic total arsenic in the World Health Organization’s «Guidelines for Drinking-water Quality» is set to 10 μg/L. With a limit of detection (LOD) of 0.9 μg/L, anodic stripping voltammetry is a viable, less sophisticated alternative to atomic absorption spectroscopy (AAS) for the determination of arsenic. While AAS (and competing methods) can only be performed in a laboratory, anodic stripping voltammetry can be used conventionally in the laboratory or alternatively in the field using the 946 Portable VA Analyzer. The determination is carried out on the scTRACE Gold electrode.

Arsenic is ubiquitous in the earth’s crust in low concentrations. Elevated levels can be found in mineral deposits and ores. Arsenic from such deposits leaches into the groundwater in the form of arsenite (AsO33–) and arsenate (AsO43–), causing its contamination. As(III) is more toxic than As(V) and shows higher mobility in the environment. The selective determination of this species is possible using the method described in this document.With a limit of detection (LOD) of 0.3 μg/L, anodic stripping voltammetry allows speciation, i.e. the specific determination of As(III). While atomic absorption spectroscopy (AAS) (and competing methods) can only determine the total element concentration, anodic stripping voltammetry is selective to the As(III) oxidation state. The determination is carried out on the scTRACE Gold electrode.

The toxicity of antimony depends on its oxidation state: antimony(III) is more toxic than antimony(V). Due to its carcinogenicity, EU legislation specifies 5 µg/L and the World Health Organization (WHO) sets a maximum concentration of 20 µg/L as the Sb(III) limit value in drinking water.Straightforward determination using anodic stripping voltammetry provides a fast (analysis time under 10 minutes) and an ultra-sensitive tool for monitoring the antimony(III) concentration in drinking water. Measurements can be performed in the laboratory with the 884 Professional VA, or alternatively in the field with the 946 Portable VA Analyzer.

The difference between the toxic and essential levels of selenium to human health are very slight. Therefore, the current provisional guideline value for selenium(IV) in the World Health Organization’s «Guidelines for Drinking-water Quality» and in the European Drinking Water Directive is set to a maximum concentration of 10 µg/L.The anodic stripping voltammetric (ASV) technique performed on the unmodified scTRACE Gold can be used to determine concentrations as low as 0.5 µg/L selenium with a 30 s deposition time. These limits can be lowered even further by increasing the deposition time. The linear range at 30 s deposition time ends at approximately 100 μg/L. The scTRACE Gold electrode does not need extensive maintenance such as mechanical polishing. Measurements can be performed in the laboratory with the 884 Professional VA or alternatively in the field with the 946 Portable VA Analyzer. This method is suited for manual or automated systems.

Tellurium is one of the elements recently identified as technologically critical for photovoltaic conversion, quantum dots, as well as in thermoelectric technology, and has the potential to become a new emergent contaminant. Until now there is no guideline value in the World Health Organization’s «Guidelines for Drinking-water Quality» and in the European Drinking Water Directive for tellurium(IV) concentration in drinking water.To monitor the tellurium(IV) levels in drinking water, anodic stripping voltammetry (ASV) performed on the unmodified scTRACE Gold is recommended. This method allows determination of tellurium(IV) in the concentration range between 1 µg/L and 60 µg/L when using a 90 s deposition time. The scTRACE Gold electrode does not need extensive maintenance such as mechanical polishing. Measurements can be performed in the laboratory with the 884 Professional VA or alternatively in the field with the 946 Portable VA Analyzer.

Monitoring Sb(III) stabilizer levels during electroless Ni plating is critical for high-quality coatings. Anodic stripping voltammetry offers fast, reliable Sb(III) analysis.

Raman spectroscopy at 532 nm excitation is used to study the crystalline and amorphous content of mixed phase silicon films.

The combination of ion chromatography and inductively coupled plasma mass spectrometry (IC-ICP/MS) is ideally suited for the detection of species of arsenic and mercury in their various oxidation levels and forms of chemical bonding. However, some species – as in the case of mercury – are reciprocally converted into one another during sample preparation, thus making a determination of the initial concentrations of the heavy metal species impossible. This article shows how these interconversions can be calculated with isotope dilution analysis and IC-ICP/MS in accordance with EPA method 6800.

This article describes an ion chromatography method for the simultaneous determination of HF, HNO3, H2SO4, short-chain organic acids, and of H2SiF6 in acid texturing baths.

This article describes the coupling of ion chromatography with mass spectrometry (IC-MS) and plasma mass spectrometry (IC-ICP/MS) for the trace analysis of potentially hazardous compounds in the environment.

The coupling of ion chromatography and inductively coupled plasma mass spectrometry (ICP/MS) leads to a high-performance measurement system that masters several particularly challenging analyses. It enables for example reliable determination of element compositions, oxidation states and chemical bonds. This information is used, for example, for assessing the toxicity of medications, environmental and water samples as well as foods and beverages.

Heavy metals such as arsenic and mercury find their way into the ground water in many regions of the world, either through natural processes or as the result of human activities. Limit values are exceeded many times over, particularly for arsenic in drinking water, in many areas. This calls for a rigorous monitoring of water quality. The present whitepaper focuses on field determinations of arsenic, mercury, and copper – directly at the sampling site.