Determination of total chromium in seawater by isotope dilution sector field ICPMS using GC sample introduction

A method for the accurate determination of total Cr in seawater by isotope dilution (ID) sector field inductively coupled plasma mass spectrometry (SF-ICPMS) using GC as a means of sample introduction is described. Chromium was reduced to Cr(III) by addition of SO(2)-saturated water and derivatized with trifluoroacetylacetonate (TFA) to form volatile Cr(TFA)(3). Derivatized analyte was either extracted into hexane or directly sampled by solid-phase microextraction (SPME) using a poly(dimethylsiloxane)-coated fused-silica fiber for GC/SF-ICPMS analysis. With medium resolution required to efficiently separate argide, argon chloride and oxide interferences, a concentration of 0.154 +/- 0.013 ng mL(-1) (1 SD, n = 4) was obtained for Cr in NRCC seawater CRM CASS-4 using a 1-microL hexane extract, in agreement with the certified value of 0.144 +/- 0.029 ng mL(-1) (95% confidence interval). A detection limit of 20 pg mL(-1) was achieved. Low-resolution GC/SF-ICPMS in combination with solvent-free SPME sampling effectively eliminated spectroscopic interferences, yielding a concentration of 0.132 +/- 0.004 ng mL(-1) (1 SD, n = 4) for Cr in CASS-4 with a method detection limit of 3.9 pg mL(-1). By comparison, SPME sampling with GC/SF-ICPMS in medium-resolution mode provided a concentration of 0.146 +/- 0.013 ng mL(-1) (1 SD, n = 4) and a method detection limit of 9.1 pg mL(-1).