Compound-Specific Hydrogen Isotope Analysis of Heteroatom-Bearing Compounds via Gas Chromatography–Chromium-Based High-Temperature Conversion (Cr/HTC)–Isotope Ratio Mass Spectrometry

Abstract

The traditional high-temperature conversion (HTC) approach toward compound-specific stable isotope analysis (CSIA) of hydrogen for heteroatom-bearing (i.e., N, Cl, S) compounds has been afflicted by fractionation bias due to formation of byproducts HCN, HCl, and H2S. This study presents a chromium-based high-temperature conversion (Cr/HTC) approach for organic compounds containing nitrogen, chlorine, and sulfur. Following peak separation along a gas chromatographic (GC) column, the use of thermally stable ceramic Cr/HTC reactors at 1100-1500 °C and chemical sequestration of N, Cl, and S by chromium result in quantitative conversion of compound-specific organic hydrogen to H2 analyte gas. The overall hydrogen isotope analysis via GC-Cr/HTC-isotope ratio mass spectrometry (IRMS) achieved a precision of better than ± 5 mUr along the VSMOW-SLAP scale. The accuracy of GC-Cr/HTC-IRMS was validated with organic reference materials (RM) in comparison with online EA-Cr/HTC-IRMS and offline dual-inlet IRMS. The utility and reliability of the GC-Cr/HTC-IRMS system were documented during the routine measurement of more than 500 heteroatom-bearing organic samples spanning a δ(2)H range of -181 mUr to 629 mUr.

Derivatization‐free method for compound‐specific isotope analysis of nonexchangeable hydrogen of 4‐bromophenol

“…The analytical precision for 4 BP is similar to that reported previously, for analysis of chlorinated ethenes using a similar thermal conversion approach and for comparable H 2 peak amplitudes . The present precision is worse than that obtained using higher thermal conversion temperature and larger mass of on‐column hydrogen . However, the high‐temperature method was deemed inappropriate for the main practical objective of analysis of 4 BP extracted from microcosm samples, due to tailing of resulting GC peaks and the larger mass of sample hydrogen required for optimum performance.…”

“…27 The present precision is worse than that obtained using higher thermal conversion temperature and larger mass of on-column hydrogen. 30,31 However, the high-temperature method was deemed inappropriate for the main practical objective of analysis of 4BP extracted from microcosm samples, due to tailing of resulting GC peaks and the larger mass of sample hydrogen required for optimum performance.…”

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

“…Indeed it is the study of analyte gas yield that has recently highlighted the potential for incomplete conversion of hydrogen within nitrogen-and other heteroatom-containing molecules into hydrogen gas during hightemperature conversion using glassy carbon. [26][27][28] The simplest means to determine whether the yield of CO 2 is quantitative for a particular material is to compare the peak size obtained in the IRMS chromatogram for a given mass of the element within the target compound with the peak size for the same mass of the element within a material known to exhibit quantitative conversion (e.g. a reference material for isotope ratio).…”

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

“…Stable isotope analysis was carried out by following closely previously published protocols for carbon (Chevallier et al, 10 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.…”

“…Hydrogen isotope analysis of halogenated compounds was achieved by using a recently developed chromium reactor (Renpenning et al, 2015) which suppresses the generation of HCl and HBr by converting halogens to CrCl3 which is trapped at the end of the reactor. This chromium reactor is connected to an Agilent 7890A GC and, via the ConFlo IV interface, to a 30 Thermo Finigan MAT 253.…”