A novel online approach to the determination of isotopic ratios for organically bound chlorine, bromine and sulphur

Abstract

A novel approach for the measurement of (37)Cl, (81)Br and (34)S in organic compounds containing chlorine, bromine, and sulphur is presented to overcome some of the major drawbacks of existing methods. Contemporary methods either require reference materials with the exact molecular compositions of the substances to be tested, or necessitate several laborious offline procedures prior to isotope analysis. In our online setup, organic compounds are separated by gas chromatography (GC) coupled to a high-temperature reactor. Using hydrogen as a makeup gas, the reactor achieves quantitative conversion of chlorinated, brominated and sulphurated organic compounds into gaseous hydrogen chloride (HCl), hydrogen bromide (HBr), and hydrogen sulphide (H(2)S), respectively. In this study, the GC interface was coupled to a quadrupole mass spectrometer operated in single-ion mode. The ion traces of either H(35)Cl (m/z 36) and H(37)Cl (m/z 38), H(79)Br (m/z 80) and H(81)Br (m/z 82), or H(2)(32)S (m/z 34) and H(2)(34)S (m/z 36), were recorded to determine the isotopic ratios of chlorine, bromine, and sulphur isotopes. The conversion interface presented here provides a basis for a novel method for compound-specific isotope analysis of halogenated and sulphur-containing compounds. Rapid online measurements of organic chlorine-, bromine- and sulphur-containing mixtures will facilitate the isotopic analysis of compounds containing these elements, and broaden their usage in fields of environmental forensics employing isotopic concepts.

Development and Validation of an Universal Interface for Compound-Specific Stable Isotope Analysis of Chlorine (37Cl/35Cl) by GC-High-Temperature Conversion (HTC)-MS/IRMS

“…Average chlorine isotope composition (δ 37 Cl raw ) during this period was measured to be 23.6 ± 0.3‰ and 25.5 ± 0.3‰ for TCE reference 2 and TCE reference 6 (n ≥ 5), respectively. In comparison, reported 17 Because of the observed stability of the system during analysis of the chlorine isotope composition of the TCE standards, four reference compounds (PCE reference 1, TCE reference 2, PCE reference 5, and TCE reference 6) were subsequently analyzed at similar conditions. Memory effects were observed during successive analysis of different compounds.…”

“…The conversion products H 35 Cl and H 37 Cl (m/z 36 and 38) were detected via qMS (gas analyzer). 17 The presented setup, however, revealed instrumental instability (1σ ≤ 1.4‰ (n = 3), delta shifts of 3.0−4.0‰ over 3 days) and referencing against the international standard (SMOC, Standard Mean Ocean Chloride) was not established. Even so, chlorine isotope analysis via HTC holds a great promise because of the universal applicability for a wide range of chlorinated compounds as well as the cost efficient incorporation into standard instrumentation for compound-specific stable isotope analysis.…”

“…Therefore, the instrumental setup previously presented by Hitzfeld et al 17 was equipped with a dual-detection system combining ion trap mass spectrometry (MS) and isotope ratio mass spectrometry (IRMS) in order to analyze HTC products and chlorine isotope composition simultaneously. Thus, we were able to identify limitations of HTC and to improve the conversion procedure.…”

Isotope Fractionation Processes of Selected Elements

“…(Hitzfeld et al 2011;Holmstrand et al 2010). The standard in use is SMOB (Standard Mean Ocean Bromine).…”

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

“…4 lower panel) [98]. This method holds great promise, because it is also universal with regard to target compounds, and it successfully performs isotope measurements by online conversion to a chlorine-containing gas.…”