Establishing a chromium-reactor design for measuring δ2H values of solid polyhalogenated compounds using direct elemental analysis and stable isotope ratio mass spectrometry

Abstract

2H/1H isotope ratios of polyhalogenated compounds were determined by elemental analysis and isotope ratio mass spectrometry (EA-IRMS). Initial measurements with standard EA-IRMS equipment, which used high-temperature pyrolysis to convert the organic compounds into hydrogen, did not achieve significant signals for polychlorinated pesticides and related compounds, presumably due to the formation of HCl instead of hydrogen. To reverse this problematic reaction, a chromium reactor was incorporated into the element analyzer system, which scavenged Cl, forming chromium chloride and releasing hydrogen again in the form of H2. The optimized system therefore allowed the delta2H values of polyhalogenated compounds to be determined. A quality assurance program was developed based on several parameters. (i) Each compound was analyzed using a sequence of five injections, where the first measurement was discarded. (ii) Recovery of H (when calculated relative to acetanilide) had to be>90% for all replicates in a sequence. (iii) All delta-values within a sequence had to vary by less than 10/1000. (iv) Results had to be reproducible on another day with a different sample scheme. Once this reproducibility had been established, variabilities in the delta2H values of organohalogen standards were investigated using the technique. The highest delta2H value of +75/1000 was found for o,p'-DDD, whereas the strongest depletion in deuterium was found for Melipax (-181/1000). The most important results for comparable compounds were as follows. DDT-related compounds gave delta2H values of between +59 and +75/1000 (technical DDT, o,p'- and p,p'-DDD) or in the range of approximately -1/1000, indicative of the different sources/methods of producing this compound. Four HCH isomers from the same supplier showed relatively similar hydrogen isotope distributions, whereas two lindane (gamma-HCH) standards from other sources had 39/1000 less deuterium. This difference is likely due to different purification steps during the isolation of pure lindane from the technical HCH mixture. An even greater difference was observed between the delta2H values of Toxaphene (US product dating from 1978) and Melipax (product from the former East Germany, dating from 1979), which gave delta2H values of -101/1000 and -181/1000, respectively, meaning that both products were easily distinguished via delta2H-IRMS. Fractioning of hydrogen isotopes in the atmospheric water cycle was suggested as one reason for the different values. In this theory, the water (which had different delta2H values depending on where it was taken from) was incorporated during the biosynthesis of camphene, which is the natural product used to produce both products. These results indicate that hydrogen isotope-specific analysis can be a valuable tool for tracing the origins of a compound in certain cases.

Recent developments in the use of isotope ratio mass spectrometry in sports drug testing

“…Replicated sample preparation and measurement of a blank urine showed comparable results after correction was applied (Table 3). Unfortunately, fluorine was found to be an inadequate derivatisation agent, with HF emerging from the ion source after short time despite the use of copper wires for removal of HF from the gas stream, destroying the ceramic thermal conversion tube and causing additional memory effects by the formation of HF during combustion [28,99]. Despite addition of hydrogen to the analyte, acetylation was found to be a reasonable derivatisation process.…”

Re‐evaluation of the hydrogen stable isotopic composition of keratin calibration standards for wildlife and forensic science applications

“…found that HTC methods using glassy carbon produce hydrogen cyanide (HCN) for nitrogenous organics. This causes a problem when normalizing the results of δ 2 H values of nitrogenous organic samples to calibration standards, such as water, that contain no nitrogen., An alternative method using elemental chromium instead of glassy carbon was described by Armbruster et al ., and was later modified by Gehre et al . Here, we tested both reactor type systems.…”

Isotopic disproportionation during hydrogen isotopic analysis of nitrogen‐bearing organic compounds

“…The method was proposed by M. Gehre during a recent IAEA consultants meeting on hydrogen reference materials and results will be published separately . It is similar to the system described by Armbruster et al . for δ 2 H measurement of solid polyhalogenated compounds.…”

“…As an alternative to the HTC technique, chromium has been used in lieu of glassy carbon, albeit at lower reaction temperatures, usually around 1000 to 1100 °C . These systems have been applied mostly to water and for reducing gaseous compounds.…”