A simplified procedure for the determination of stable chlorine isotope ratios (delta Cl-37) using LA-MC-ICP-MS

Stable chlorine isotopes (Cl-37, Cl-35) are considered as important tracers of geochemical processes, especially in subduction zone systems. However, high-quality chlorine isotope data are scarcely available. Here we present a comparatively simple procedure for the precise and accurate determination of stable chlorine isotope ratios (delta(37) Cl) using LA-MC-ICP-MS. Chlorine was extracted from solid samples by pyrohydrolysis. After quantitative precipitation as AgCl the dried precipitates where analysed in a sample-standard bracketing approach using a weak laser ablation (0.3 J/cm(2)) for sample evaporation. Atlantic Ocean sea salt and the sea water standard IAPSO were used as SMOC ( standard mean ocean chloride) for normalisation (delta Cl-37 = 0 parts per thousand). The precision and accuracy of the presented method was validated analysing the reference materials JB-1a and JB-2. The chlorine isotope ratios of these standards were determined as delta Cl-37(JB-1a) = (-0.99 +/- 0.06) parts per thousand and delta Cl-37(JB-2) = (-0.60 +/- 0.03)parts per thousand( errors 2SE), respectively, in accordance with published data. Applying the presented method a total amount of less than 1 mu g of chlorine was consumed during a typical measurement including 10 ablation periods on the sample.