Kristof Tirez

Determination of hexavalent chromium by species specific isotope dilution mass spectrometry and ion chromatography–1,5-diphenylcarbazide spectrophotometry

The accuracy of the determination of hexavalent chromium (Cr6+) in solid matrices remains a challenging field of effort and improvement. An alkaline digestion (0.5 M NaOH–0.28 M Na2CO3) followed by ion chromatography and spectrophotometric determination by post-column derivatisation with 1,5-diphenylcarbazide (DPC) provides accurate and reproducible results. To gain a better insight into the species interconversion during the digestion, the concept of species specific isotope dilution mass spectrometry by adding enriched chromium isotopes that have been chemically converted into trivalent (Cr3+) and hexavalent chromium was used. For the analysis of the digestion solutions ion chromatography coupled to inductively coupled plasma-mass spectrometry (IC-ICP-MS) was peformed. The limit of detection in the digestion solution by the latest technique amounted 0.8 ng ml−1 Cr6+. The accuracy of an alkaline digestion on solid waste materials was compared with a water extraction (leaching test industrial waste), indicating that the alkaline digestion is accurate from the point of view of minimal species interconversion on one hand and the maximum amount of Cr6+ extracted on the other, while significant oxidation and reduction reactions were observed during leaching tests with water. In the framework of European Directive 94/62/EC on Packaging and Packaging Waste, the developed analytical method has been used to compare the concentrations of Cr6+ on 40 packaging materials against the regulatory limit value of 100 mg kg−1 by weight (sum of concentration levels of lead, cadmium, mercury and hexavalent chromium).

Characterization of inorganic selenium species by ion chromatography with ICP-MS detection in microbial-treated industrial waste water

Microbial selenium reduction was investigated for application in the removal of selenium from industrial waste water. This paper presents the results of the development of a routine ICP-MS method for the determination of inorganic selenium species in microbial-treated industrial waste water. For the speciation of water soluble inorganic selenium species (selenate and selenite) two different anion exchange columns were compared. The column separation performance for the determination of selenium was investigated for both inorganic and some organic selenium species. The increase in sensitivity for selenium after the addition of carbon-containing solutions was investigated by the addition of increasing amounts of ethanol to the eluent. The optimum addition level of 2% v/v ethanol resulted in a sensitivity enhancement factor of 5 under the given instrumental settings of the ICP-MS. The ICP-MS instrument showed good long-term stability (3% over 40xa0h), as shown by the analysis of two independent control standards after every 10 samples with addition of arsenobetaine as the internal standard. The different selenium species showed the same signal sensitivity, resulting in a quantification limit of 1xa0µgxa0l−1 per species. Over 600 microbial-treated waste water samples were characterized for selenate and selenite content. A selenium compound present in some of the samples could not be identified. No evidence of DL-selenocystine and DL-selenomethionine and DL-selenoethionine could be found. The microbial removal of selenium from industrial waste water was at first hampered by the presence of nitrate (denitrification) and the partial reduction of selenate was observed after the complete removal of selenite to the metallic form.

Speciation and fractionation of nickel in airborne particulate matter: comparison between selective leaching and XAS spectroscopy

Nickel speciation and fractionation using a multidisciplinary approach are discussed for different particulate matter samples collected in industrial and rural atmospheres. The technologies utilized in this research span from X-ray Absorption Near Edge Structure (XANES) and X-Ray Diffraction (XRD) to a wet chemistry sequential leaching assay (including determination by inductively coupled plasma atomic emission spectroscopy, ICP-AES). The Zatka sequential leaching method provides an inexpensive assay to differentiate among ‘soluble’, ‘sulfidic’, ‘metallic’, and ‘oxidic’ chemical forms of Ni. The XANES technique is especially well suited for Ni speciation between and to a lesser extent within the 4 defined Ni species groups of the Zatka sequential leaching procedure. Limitations for interpretation in the present study with respect to XANES are the availability of pure phase Ni species for uptake as reference spectra and the collinearity between the spectra of Ni compounds within a Ni species group (e.g. NiSO4·6H2O and Ni(NO3)2·6H2O). The Ni speciation and fractionation results on the particulate matter samples reflect in general a good agreement between the modified Zatka sequential leaching procedure and the XANES data. For the particulate matter collected in and close to a stainless steel factory, Ni included in a spinel structure (NiFe2O4) was identified as the principal Ni species. The particulate matter collected in rural atmosphere showed a 50/50 distribution between soluble and oxidic Ni species.

Use of Compound-Specific Nitrogen (d 15 N), Oxygen (d 18 O), and Bulk Boron (d 11 B) Isotope Ratios to Identify Sources of Nitrate-Contaminated Waters: A Guideline to Identify Polluters

The use of various isotopes (d15N, d18O & d11B) to identify the sources of nitrate (NO3 −) present in natural waters is described. Then a new guideline of how to apply the multi-isotope approach is presented. This guideline is written for policy makers and scientists who are involved in the different steps and processes related to nitrate contaminated waters including monitoring and data interpretation. NO3 − is a common pollutant in water (both surface and groundwater). In several water bodies over Europe, point measurements identify that the level of this pollutant is higher than the reference value of 50 mgL−1, defined by the European Union (EU) Water Framework Directive 2000/60/EC (European Parliament, 2000). This directive also states that all waters have to reach a “good status” (i.e., good quality) by 2015. This statement implies that EU member states have to take actions to achieve this goal. One of the major obstacles with NO3 − contamination in water is the identification of the corresponding source(s) of pollution, a prerequisite for properly designing appropriate actions and remediation. Recent studies have proven the added value of analyzing compound specific isotopic signature (CSIA) of nitrate (both nitrogen (d15N), oxygen (d18O) and bulk boron (d11B) isotopic composition) to define the origin/source of NO3 − in waters. This definition is possible because different sources of nitrate have distinct isotopic signatures. The recent EU-LIFE ISONITRATE project demonstrated the benefit of the multi-isotope approach, while the presented guideline to implement this method is one of the outcomes of this project. More details on the scientific results of ISONITRATE are available at http://isonitrate.brgm.fr/.

Determination of bromate in drinking waters using low pressure liquid chromatography/ICP-MS

This paper describes a user-friendly method for bromate determination that can be implemented easily on any inductively coupled plasma-mass spectrometer present in drinking water laboratories. The method uses low pressure liquid chromatography coupled to an ICP-quadrupole mass spectrometry instrument (ICP-QMS) or an ICP-sector field mass spectrometry instrument (ICP-SFMS) and is compared to that relying on high performance liquid chromatography (HPLC) coupled to an ICP-QMS instrument. The low pressure LC/ICP-MS method uses a low-pressure delivery six-port valve and a 5 cm anion exchange column, which allows a fully resolved separation of bromate in 13 min and achieves a limit of quantification of 0.2 μg bromate L−1. The low pressure LC system is small and easy to install and its operation is fully integrated within the ICP-MS software. The method allows fit-for-purpose assessment of bromate, potentially present as a Br-containing disinfection by-product in drinking water, and meets all performance characteristic requirements set by the European Council for the monitoring of the quality of water intended for human consumption. A median bromate concentration of 0.5 μg L−1 was obtained for 80 tap water samples collected during regulatory monitoring campaigns from 2009 until 2012 and covering different water supply areas in the Flemish region of Belgium.

Total uncertainty budget as method evaluation criterion for the determination of tracer (111Cd) cadmium and indigenous cadmium in soil column effluents with ICP-MS

For the evaluation of different analytical methods the best achievable final uncertainty can be used as the criterion. Evaluation of an analytical method on this basis includes the magnitude and also the robustness of the uncertainty budget. This evaluation was applied to laboratory-scale migration experiments on soil columns. These experiments were performed in order to estimate soil transport parameters of heavy metal pollutants (cadmium). In these studies a tracer (stable 111Cd isotope), having nearly the same physico-chemical properties as the pollutant of concern, was added on top of a contaminated soil and the column effluents were fractionally collected at the bottom. This paper presents three different calculation models, derived from the isotope dilution equation, for the simultaneous determination of the concentration tracer cadmium, [Cdt], and indigenous cadmium, [Cdn], in soil column effluents with ICP-MS. The methods differ in the method of calculation but are, in principal, based on the same measurements. The uncertainty budgets of the different methods were used in the evaluation. In addition to the magnitude of the total uncertainty, the boundary conditions of some parameters were investigated in detail. The influence of the following parameters on the uncertainty budget was studied: the concentration level of cadmium, the isobaric interference of tin and the molar fraction of indigenous cadmium.

Full uncertainty calculation on quantitative determination of tracer (111Cd) cadmium and natural cadmium in soil column effluents with ICP-MS

In laboratory-scale migration experiments a tracer (stable 111 nCd isotope) is added on top of a contaminated soil and the column effluents are fractionally collected. This paper describes an analytical method for the simultaneous low level quantitative determination with inductively coupled plasma mass spectrometry (ICP-MS) of contaminant (natural) and tracer ( n 111 nCd) cadmium in soil column effluents by adaptation of the isotope dilution equation. For the calculation of the full uncertainty on the quantitative determination of tracer and natural cadmium, a method has been proposed emphasising the practical, realistic approach of estimating uncertainties based on statistical assumptions. The GUM Workbench© program, the computations of which follow the rules of the ‘ISO guide to the expression of uncertainty in measurement’, was used. At low concentrations of cadmium (<0.2 ng ml n –1 n Cd) the uncertainty due to counting statistics is the major source of uncertainty. At higher concentrations the signal instability of the ICP-MS instrument, partially due to clogging of the sampling cone by calcium salts present in the leachant (1 mM CaCl n 2 n), forms the largest contribution to the total uncertainty. For concentrations of 0.5 ng ml n –1 n Cd and higher, the expanded uncertainty U amounts to ±4% (coverage factor 2; 95% probability).