Chlorine Isotope Analysis of Submicromole Organochlorine Samples by Sealed Tube Combustion and Thermal Ionization Mass Spectrometry

Abstract

Improved sensitivity in the analysis of stable chlorine isotopes of organochlorines (delta(37)Cl-OCl) has been established using sealed tube combustion in conjunction with thermal ionization mass spectrometry (TIMS). TIMS of chlorine isotopes was performed on <85 nmol of Cl with an achievable precision of <0.25 per thousand for pure inorganic chloride samples and 0.46 per thousand for chloride liberated from organochlorines (OCls). This makes possible significant reductions in the overall sample size requirement, as compared to the techniques of gas source stable isotope ratio mass spectrometry (SIRMS). Yields in excess of 99% were demonstrated in the dechlorination of <0.14 micromol 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), and the overall yield, including purification of liberated chloride, was 86-97%. The accuracy of TIMS in the measurement of chlorine isotopes derived from OCls was confirmed by analysis of a DDT sample previously analyzed with SIRMS.(9) Using the described method for TIMS, the DDT sample gave a bulk chlorine isotope ratio of delta(37)Cl -4.42 +/- 0.46 per thousand (1sigma). The reported value from SIRMS analysis is -4.34 +/- 0.25 per thousand, indicating the conformity of the two methods.

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

“…Offline chlorine isotope analysis traditionally relies on either conversion to chloromethane (for dual inlet-IRMS analysis [92][93][94]) or caesium chloride (for thermal ion mass spectrometry analysis [95,96]). In a recent development, several innovative solutions for GC coupling have been proposed, each based on a different strategy (Fig.…”

Compound-Specific Chlorine Isotope Analysis: A Comparison of Gas Chromatography/Isotope Ratio Mass Spectrometry and Gas Chromatography/Quadrupole Mass Spectrometry Methods in an Interlaboratory Study

“…Continuous flow chlorine isotope analysis has been prevented by the necessity of converting compounds into analytes such as methyl chloride 11 or cesium chloride 12 which cannot be generated online in a carrier gas flow. Offline analysis, on the other hand, is carried out on bulk samples, which requires tedious separation of compounds from interfering components.…”

Monitoring and evaluation of dechlorination processes using compound‐specific chlorine isotope analysis

“…Compound‐specific stable isotope analysis (CSIA) using gas chromatography/isotope ratio mass spectrometry (GC/IRMS) is a rapidly emerging analytical method, especially in environmental sciences, with an array of applications. The molecular isotopic signature of environmental contaminants can be used to trace their sources on a local to global scale, serving as an ideal tool in 'environmental forensics', or to identify, characterize and quantify biotic and abiotic transformation reactions 1–5…”

“…Chlorine has a number of isotopes, of which only two stable isotopes occur naturally: 35 Cl with a natural abundance of 75.78% and 37 Cl with a natural abundance of 24.22% 8. Unlike carbon isotope analysis, chlorine isotope analysis by traditional methods cannot be carried out without upstream, labor‐intensive, offline pretreatments to convert chlorinated compounds into a molecule containing a single chlorine atom, such as methyl chloride (CH 3 Cl) or cesium chloride (CsCl) 4, 9–15. After conversion into methyl chloride, the chlorine isotope ratio is determined using dual‐inlet isotope ratio mass spectrometry (DI‐IRMS).…”