Determination of ¹³C/¹²C Isotopic Ratios of Biogenic Organometal(loid) Compounds in Complex Matrixes

Abstract

Methylated metal(loid) compounds are formed in the environment by abiotic as well as enzymatically catalyzed transfer of a methyl group. Due to the increased mobility and toxicity in comparison to the inorganic precursors, the investigation of the formation process is of high relevance. Though the natural abundance carbon isotope ratio can give important insights toward their origin as well as the biochemical methyl transfer process, so far, these species have not been investigated by carbon isotope ratio mass spectrometry (IRMS). This is due to the analytical challenge to precisely determine the natural isotope distribution of trace amounts of metal(loid)-bound carbon in complex organic matrixes. To overcome this problem, we tested the concept of selective derivatization of nonvolatile organometal(loid)s by hydride generation (HG) followed by purge and trap (P-T) enrichment, heart-cut gas chromatography (hcGC), and subsequent analysis by GC/IRMS. Parameter optimization of HG/P-T/hcGC was conducted using online coupling to element-sensitive ICPMS (inductively coupled plasma mass spectrometry) detection. The purity of the HG/P-T/hcGC fraction was verified by GC/MS. For the model substance trimethylarsine oxide (TMAsO), an excellent agreement of the delta(13)C-value analyzed by HG/P-T/hcGC-GC/IRMS was achieved in comparison to the bulk delta(13)C-value, which shows that no significant isotope fractionation occurred during hydride generation and subsequent separation. The optimized method showed good reproducibility and a satisfying absolute detection limit of 4.5 microg TMAsO (1.2 microg(carbon)). This method was applied to the analysis of TMAsO in compost. The low delta(13)C value of this compound (-48.38 +/- 0.41 per thousand) indicates that biomethylation leads to significant carbon fractionation. HG/P-T/hcGC-GC/IRMS is a promising tool for investigation of the biomethylation process in the environment.

Current challenges in compound-specific stable isotope analysis of environmental organic contaminants

“…modifications are decarboxylation [108,109], reduction of fatty acid esters to alcohols [110], reduction of organometal (loid) oxides to the corresponding hydrides [111], intramolecular esterification [112], or selective fragmentation [89]. Besides enabling carbon-isotope analysis, the latter approach has been shown to facilitate isotope analysis of nitrogen and hydrogen also [65,89].…”

Mechanism of multi‐metal(loid) methylation and hydride generation by methylcobalamin and cob(I)alamin: a side reaction of methanogenesis

“…For oxidation‐state specific HG, subsequent P‐T enrichment, and GC, a self‐developed semi‐automated system was used that has been described elsewhere . The introduction of a second trap (Fig.…”

“…For oxidation-state specific HG, subsequent P-T enrichment, and GC, a self-developed semi-automated system was used that has been described elsewhere. [21] The introduction of a second trap ( Fig. 2) allowed a new oxidation-state specific hydride generation technique, which is a two-step method using the pH dependence of the formation of volatile hydrides.…”

Practical and theoretical considerations for the determination of δ13CVPDB values of methylmercury in the environment

“…While there have been some studies into the carbon isotope analysis of organometallic compounds using hydride generation (e.g. 13,14 ), the carbon isotope ratio analysis of MeHg or other organomercury compounds has not been extensively studied in the past, although Masbou and colleagues have published a comparison of three different approaches for the analysis of MeHg by gas chromatography/ combustion-isotope ratio mass spectrometry (GC/C-IRMS). 15 Thus far, however, carbon isotope ratios of MeHg that are fully traceable to the international Vienna Peedee Belemnite (VPDB) scale have not been reported.…”

“…In this work we have developed methods and derived uncertainty budgets for the fully VPDB-traceable carbon isotope ratio determination of MeHg with the aim of studying MeHg within fish tissues. Reference compounds/materials for method development were identified, then characterized for their bulk δ 13 C VPDB values by flow injection/chemical oxidation-isotope ratio mass spectrometry (FIA/CO-IRMS). Two methods for the determination of compound-specific MeHg δ 13 C VPDB values by GC/C-IRMS were developed, with and without derivatization.…”