METHOD OPTIMIZATION AND QUALITY ASSURANCE IN SPECIATION ANALYSIS USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH DETECTION BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

Achievement of optimum selectivity, sensitivity and robustness in spec iation analysis using high performance liquid chromatography (HPLC) wi th inductively coupled mass spectrometry (ICP-MS) detection requires t hat each instrumental component is selected and optimized with a view to the ideal operating characteristics of the entire hyphenated system . An isocratic HPLC system, which employs an aqueous mobile phase with organic buffer constituents, is well suited for introduction into the ICP-MS because of the stability of the detector response and high deg ree of analyte sensitivity attained. Anion and cation exchange HPLC sy stems, which meet these requirements, were used for the separation of selenium and arsenic species in crude extracts of biological samples. Furthermore, the signal-to-noise ratios obtained for these incompletel y ionized elements in the argon ICP were further enhanced by a factor of four by continuously introducing carbon as methanol via the mobile phase into the ICP. Sources of error in the HPLC system (column overlo ad), in the sample introduction system (memory by organic solvents) an d in the ICP-MS (spectroscopic interferences) and their prevention are also discussed. The optimized anion and cation exchange HPLC-ICP-MS s ystems were used for arsenic speciation in contaminated ground water a nd in an in-house shrimp reference sample. For the purpose of verifica tion, HPLC coupled with tandem mass spectrometry with electrospray ion ization was additionally used for arsenic speciation in the shrimp sam ple. With this analytical technique the HPLC retention time in combina tion with mass analysis of the molecular ions and their collision-indu ced fragments provide almost conclusive evidence of the identity of th e analyte species. The speciation methods are validated by establishin g a mass balance of the analytes in each fraction of the extraction pr ocedure, by recovery of spikes and by employing and comparing independ ent techniques. The urgent need for reference materials certified for elemental species is stressed. (C) 1998 Elsevier Science B.V.