| Abstract
| - Here we describe an on-line method for measuring δ37Clvalues of chloride bearing salts, waters, and organicmaterials using multicollector continuous-flow isotoperatio mass spectrometry (CF-IRMS). Pure AgCl quantitatively derived from total Cl in water, inorganic Cl salts,and biological samples was reacted with iodomethane inevacuated 10-mL stopper sealed glass vials to producemethyl chloride gas. A GV Instruments Multicollector CF-IRMS with CH3Cl optimized collector geometry was modified to accommodate a headspace single-sample gasinjection port prior to a GC column. The GC column wasa 2-m Porapak-Q packed column held at 160 °C. Theresolved sample CH3Cl was introduced to the IRMSsource in a helium stream via an open split. δ37Cl valueswere calculated by measurement of CH3Cl at m/z 52/50and by comparison to a reference pulse of CH3Cl calibrated to standard mean ocean chloride. Sample CH3Clanalysis time was ∼6 min. Injections of 40 μL of pure CH3Cl gas yielded a repeatability (±SD) of ±0.06‰ for δ37Cl(n = 10). Combined GC and IRMS source linearity forCH3Cl was <0.2‰/nA (V) peak height. External repeatability, based on processing of seawater and NaCl reference solutions, was better than ±0.08‰. The smallestsample for δ37Cl analysis by this method was ∼0.2 μmolof Cl. Selected results from a river basin and biologicalsamples study illustrate the potential of on-line chlorineisotope assays in environmental pollution studies.
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