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Abstract:
RATIONALE: Accurate hydrogen isotopic analysis of halogen- and sulfur-bearing organics
has not been possible with traditional high-temperature conversion (HTC) because the
formation of hydrogen-bearing reaction products other than molecular hydrogen (H
2
) is
responsible for non-quantitative H
2
-yields and possible hydrogen isotopic fractionation. Our
previously introduced, new chromium-based EA-Cr/HTC-IRMS (Elemental Analyzer –
Chromium/High Temperature Conversion – Isotope-Ratio Mass Spectrometry) technique
focused primarily on nitrogen-bearing compounds. Several technical and analytical issues
concerning halogen- and sulfur-bearing samples, however, remained unresolved and required
further refinement of the reactor systems.
METHODS: The EA-Cr/HTC reactor was substantially modified for the conversion of
halogen- and sulfur-bearing samples. The performance of the novel conversion setup for solid
and liquid samples was monitored and optimized using a simultaneously operating dual-
detection system of IRMS and ion trap MS. The method with several variants in the reactor,
including the addition of manganese metal chips, was evaluated in three laboratories using
EA-Cr/HTC-IRMS (on-line method) and compared with traditional uranium-reduction-based
conversion combined with manual dual-inlet IRMS analysis (off-line method) in one
laboratory.
RESULTS: The modified EA-Cr/HTC reactor setup showed an overall H
2
-recovery of more
than 96 % for all halogen- and sulfur-bearing organic compounds. All results were
successfully normalized via 2-point calibration with VSMOW-SLAP reference waters.
Precise and accurate hydrogen isotopic analysis was achieved for a variety of organics
containing F-, Cl-, Br-, I-, and S-bearing heteroelements. The robust nature of the on-line
EA-Cr/HTC technique was demonstrated by a series of 196 consecutive measurements with a
single reactor filling.
CONCLUSIONS: The optimized EA-Cr/HTC reactor design can be implemented in existing
analytical equipment using commercially available material and is universally applicable for
both heteroelement-bearing and heteroelement-free organic-compound classes. The
sensitivity and simplicity of the on-line EA-Cr/HTC-IRMS technique provide a much needed
tool for routine hydrogen-isotope source tracing of organic contaminants in the environment.
