Alleviation of polyatomic ion interferences for determination of chlorine isotope ratios by inductively coupled plasma mass spectrometry.

A simple variation in sample preparation and introduction allows the measurement of chlorine isotope ratios by inductively coupled plasma mass spectrometry (ICP/MS). Dissolution of the sample in D2O rather than H2O attenuates the major polyatomic ion (36)ArH(+) and frees m/z 37 for determination of (37)Cl(+). The isotope ratio (35)Cl/(37)Cl in a 50 mg/L solution of Cl as LiCl is determined with a relative standard deviation of 0.21%. Sample memory is low, as the (35)Cl signal decays to less than 1% of its original value after ∼2 min of cleanout with D2O . The detection limit for Cl using this procedure is approximately 20 μg/L.