Establishing a chromium-reactor design for measuring delta H-2 values of solid polyhalogenated compounds using direct elemental analysis and stable isotope ratio mass spectrometry

H-2/H-1 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 H-2. The optimized system therefore allowed the delta H-2 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 parts per thousand. (iv) Results had to be reproducible on another day with a different sample scheme. Once this reproducibility had been established, variabilities in the delta H-2 values of organohalogen standards were investigated using the technique. The highest delta H-2 value of +75 parts per thousand was found for o,p'-DDD, whereas the strongest depletion in deuterium was found for Melipax (-181 parts per thousand). The most important results for comparable compounds were as follows. DDT-related compounds gave delta H-2 values of between +59 and +75 parts per thousand (technical DDT, o,p'- and p,p'-DDD) or in the range of approximately -1 parts per thousand, 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 parts per thousand 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 delta H-2 values of Toxaphene (US product dating from 1978) and Melipax (product from the former East Germany, dating from 1979), which gave delta H-2 values of -101 parts per thousand and -181 parts per thousand, respectively, meaning that both products were easily distinguished via delta H-2-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 delta H-2 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.