Trace lead measurement and on-line removal of matrix interference in seawater by isotope dilution coupled with flow injection and ICP-MS

Isotope dilution analysis method coupled with flow injection and inductively coupled plasma mass spectrometry (ID-FI-ICP-MS), enabled trace lead concentration in seawater to be determined and the high salt concentration in the matrix, such as Na⁺, Ca²⁺ and Mg²⁺, to be removed on-line. The operational parameters of the FI system including pH for the chelating reaction, concentration of 8-hydroxyquinoline-5-sulfonic acid (8-HQS), sample loading time and injection speed, washing time and speed, eluting acid concentration and eluting speed, and instrumental parameters for ICP-MS were optimized and selected. Accurate results could be achieved because the isotope ratios required can be precisely measured in the range of the eluting peak by means of ID-FI-ICP-MS. The 3σ detection limit was 0.204 ng ml⁻¹. The trace lead concentration of seawater in south Xiamen, China was 0.988 ± 0.039 ng ml⁻¹. The recoveries of spiked Pb standard in seawater and standard reference water (GBW 08607) were 97.9 and 101.0%, respectively, with a relative standard deviation of 0.98%. This method can be used to determine trace lead concentration in high salt matrix samples, and is especially useful when the eluting peaks do not have a Gaussian-distribution.