Article pubs.acs.org/ac
Isotope Analysis of Sulfur, Bromine, and Chlorine in Individual Anionic Species by Ion Chromatography/Multicollector-ICPMS Yevgeni Zakon,†,‡ Ludwik Halicz,†,§ and Faina Gelman*,† †
Geological Survey of Israel, 30 Malkhei Israel St., Jerusalem, 95501, Israel Department of Chemistry, The Hebrew University, Jerusalem, 91904, Israel § Biological and Chemical Research Centre, University of Warsaw, Warsaw, 02-089, Poland ‡
ABSTRACT: We developed an analytical method for precise and accurate analysis of δ34S, δ81Br, and δ37Cl in individual anionic species by coupled ion chromatography (IC) and multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The method is based on the online separation and purification of ions by IC prior to their isotope analysis by MC-ICPMS. The developed technique significantly simplifies δ34S, δ81Br, and δ37Cl analysis in environmental samples. In cases when several anionic species of the same element are present in the sample, they might be analyzed in a single analytical run. Major isobaric interferences for the analyzed elements were reduced by using “dry” plasma conditions and applying sufficient mass resolution power. The sample-standard bracketing technique was used for instrumental drift correction. In the case of δ34S analysis, precisions up to 0.15‰ (1sd) have been achieved for analytes containing down to 5 nmol of S; for δ81Br, the attained precision was 0.1‰ (1sd) for analytes containing down to 0.6 nmol of Br. Precisions of 0.2‰ have been obtained for δ37Cl with analytes containing 0.7 μmol of Cl. Robustness of the developed analytical method, as well as high precisions and accuracies, has been demonstrated for the laboratory standard solutions and for environmental samples.
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reported good results for seawater samples after NaCl was added to the working standards to match the analyte matrix. Although the reported results are promising, several limitations could be expected. Thus, if the samples contain several sulfur species (for example, sulfate, sulfide, and organic sulfur), the measured δ34S value represents the bulk value and cannot be related to a specific S-containing anion. Another drawback of the method is a potential clogging of the MC-ICPMS interface cones due to introduction of high salinity solutions. Several precise analytical techniques have been proposed for δ81Br and δ37Cl determination.23−29 Nevertheless, isotope analysis of inorganic bromides and chlorides remains challenging due to the complex procedure of sample preparation. For example, one of the techniques is based on the off-line sample preparation that includes halide precipitation in the form of silver halide, followed by its conversion to a volatile methyl halide and measurement of δ37Cl or δ81Br by gas source IRMS.28,30 Another sample preparation technique involves offline conversion into cesium salts prior to analysis by thermal ionization mass spectrometry (TIMS).27,29 Recently, our research group proposed an online procedure for δ81Br determination in inorganic bromides. The method is based on the wet oxidation of inorganic bromide into molecular
he isotope composition of sulfur, chlorine, and bromine in organic and inorganic species can provide unique data for studying natural biogeochemical processes,1−6 water contamination,7,8 and natural attenuation mechanisms.9 During the last decades, isotope analysis of carbon, hydrogen, and nitrogen in organic compounds by gas chromatography (GC) coupled to an isotope ratio mass spectrometer (IRMS) has become a strong analytical tool in environmental, forensic, biochemical, and geochemical sciences.10,11 In recent years, compound-specific isotope analysis of Hg, S, Br, and Cl by GC-multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) has been established.12−16 However, isotope analysis of inorganic S, Br, and Cl still remains a complex task requiring a tedious off-line sample preparation. Currently, one of the conventional methods for δ34S analysis of sulfate is based on sulfate precipitation as BaSO4, followed by combustion to SO2 in an elemental analyzer (EA)17,18 and measurement of 34S/32S ratios in a gas-source IRMS. Although sufficient precision may be obtained by this procedure, its main drawback is the laborious sample preparation. Recently, δ34S analysis by MC-ICPMS has been proposed by several research groups.5,19−21 High precisions of up to 0.1‰ (2sd) for analytes containing purified sulfate have been demonstrated; however, extensive separation of sulfate was necessary in complex environmental samples. Recently, Lin et al.22 deployed matrixmatched working standards to directly measure the sulfur isotopic composition in water samples without chemical purification. They © 2014 American Chemical Society
Received: March 19, 2014 Accepted: June 3, 2014 Published: June 3, 2014 6495
dx.doi.org/10.1021/ac5010025 | Anal. Chem. 2014, 86, 6495−6500
Analytical Chemistry
Article
bromine which is transferred into the MC-ICPMS by continuous flow of helium.25 However, some precautions are necessary for performing the procedure due to hazardous and corrosive properties of bromine. The objective of the present study was to develop a method for online determination of δ34S, δ81Br, and δ37Cl in individual inorganic anionic species. Considering the advantages of hyphenated techniques like GC-MC-ICPMS for compoundspecific isotope analysis,12,13,15,16 our approach was based on interfacing an ion chromatograph with MC-ICPMS. The instrumental setup enables isotope analysis of the desired individual ionic species directly after their online separation and purification by IC.
situ with the KOH eluent (30 mM), and transported through the guard column into the analytical ion chromatography column. After that, the sample passed through the suppressor, where exchange of cations with H+ was accomplished. Passing the detector, the eluent (pH ∼ 5) was nebulized into the Apex Q desolvation unit and introduced into the MC-ICPMS. The suppressor unit was continuously rinsed with a 0.2 μM solution of H2SO4. The IC eluent flow of 0.45 mL/min was applied to fit the optimal flows of nebulizer and the MC-ICPMS sample introduction system. Samples were analyzed for isotopic composition using a MC-ICPMS (Nu Plasma II, UK) equipped with 16 Faraday cups. The instrumental working parameters are listed in Table 1.
EXPERIMENTAL SECTION Materials. High purity water with conductivity
