Compound Specific Stable Chlorine Isotopic Analysis of Volatile Aliphatic Compounds Using Gas Chromatography Hyphenated with Multiple Collector Inductively Coupled Plasma Mass Spectrometry

Abstract

Stable chlorine isotope analysis is increasingly used to characterize sources, transformation pathways, and sinks of organic aliphatic compounds, many of them being priority pollutants in groundwater and the atmosphere. A wider use of chlorine isotopes in environmental studies is still inhibited by limitations of the different analytical techniques such as high sample needs, offline preparation, confinement to few compounds and mediocre precision, respectively. Here we present a method for the δCl determination in volatile aliphatic compounds using gas chromatography coupled with multiple-collector inductively coupled plasma mass spectrometry (GC-MC-ICPMS), which overcomes these limitations. The method was evaluated by using a suite of five previously offline characterized in-house standards and eight chlorinated methanes, ethanes, and ethenes. Other than in previous approaches using ICP methods for chlorine isotopes, isobaric interference of the ArH dimer withCl was minimized by employing dry plasma conditions. Samples containing 2-3 nmol Cl injected on-column were sufficient to achieve a precision (σ) of 0.1 mUr (1 milliurey = 0.001 = 1‰) or better. Long-term reproducibility and accuracy was always better than 0.3 mUr if organics were analyzed in compound mixtures. Standardization is carried out by using a two-point calibration approach. Drift, even though very small in this study, is corrected by referencing versus an internal standard. The presented method offers a direct, universal, and compound-specific procedure to measure the δCl of a wide array of organic compounds overcoming limitations of previous techniques with the benefits of high sensitivity and accuracy comparable to the best existing approaches.

Isotopic Characterization (2H, 13C, 37Cl, 81Br) of the Abiotic Sinks of Methyl Bromide and Methyl Chloride in Water and Implications for Future Studies.

“…Further proof for this assumption was also delivered by the chlorine isotopic measurements. CH3Cl used for the experiments had a δ 37 Cl of +6.02 mUr SMOC (Horst et al, 2017) whereas Clin salt should be close to 0 mUr SMOC (Shouakar-Stash et al, 2005). In our experiments the reaction caused a shift of δ 37 Cl towards heavier values following clearly first order kinetics (Fig S1.5).…”

“…Stable isotope analysis was carried out by following closely previously published protocols for carbon (Chevallier et al, 2018), hydrogen (Renpenning et al, 2015), chlorine (Horst et al, 2017;Renpenning et al, 2018) and bromine (Horst et al, 2011). Subsequently a brief description is provided for each method.…”

“…For chlorine, a two-point calibration approach was applied to normalize raw-δ 37 Cl values to the SMOC scale (Standard Mean Ocean Chloride). Three organic in-house reference compounds (TCE-2, TCE-6, CH3Cl) are typically used for this procedure (Horst et al, 2017). The accuracy for the analysis of a single sample is better than 0.2 mUr.…”

Liquid chromatography/isotope ratio mass spectrometry analysis of halogenated benzoates for characterization of the underlying degradation reaction in Thauera chlorobenzoica CB‐1T

“…However, at the moment this method is only applicable for single isotope analysis. The isotope composition of other elements such as chlorine, bromine or hydrogen, which may reveal interesting insights into reaction mechanisms, can at the moment only be analyzed after derivatization by GC/Cr/HTC‐IRMS or GC/ICP‐MS …”

“…Moreover, 1 nmol C has to be injected for halogenated benzoates to yield stable isotope ratios by this LC/IRMS method, whereas the sensitivity limits for GC/IRMS are described as 0.1-5 nmol. 32 Whereas no significant isotopic fraction was visible for 4-Cl-benzoate, 3-Cl-benzoate and 3-Br-benzoate reveal significant inverse carbon isotopic fractionation moment only be analyzed after derivatization by GC/Cr/HTC-IRMS 33 or GC/ICP-MS. 34,35…”