A simple method for high-precision isotopic analysis of chlorine via pneumatic nebulization multi-collector inductively coupled plasma-mass spectrometry

Abstract

Chlorine isotope ratio measurement using multi-collector ICP-mass spectrometry (MC-ICP-MS) with sample introduction using traditional pneumatic nebulization suffers from spectral interference in addition to low sensitivity. Pronounced memory effects may jeopardize the accuracy of the results and/or the sample throughput. In this work, these limitations were overcome by using (i) high mass resolution (mass resolving power of about 10 000) to resolve spectral interference, (ii) 5 mmol L⁻¹ NH₄OH as wash solution to avoid memory effects and (iii) a Cl concentration of ≥70 mg L⁻¹. The major cation load of seawater and chloride salts (NaCl, KCl) sample solutions was efficiently removed without affecting the original isotopic composition of Cl via cation exchange chromatography with Dowex® 50WX8 resin. The method developed was demonstrated to be accurate and precise, as attested by the measurement result for the ³⁷Cl/³⁵Cl isotope ratio in NIST SRM 975a (experimental value of 0.319765 ± 0.000022, compared to a reference value of 0.319768 ± 0.000187 and a precision of ∼0.007% RSD, n = 3), additionally, the δ³⁷Cl value (vs. standard mean ocean chlorine, SMOC) was determined for five different standards; the values ranged from −0.54 to +0.89‰.