Advantages and limitations of a desolvation system coupled online to HPLC-ICPqMS/ES-MS for the quantitative determination of sulfur and arsenic in arseno-peptide complexes

Abstract

High sulfur detection limits, mainly caused by the interfering O₂⁺ ions, made simultaneous sulfur and arsenic speciation analysis by on-line coupling of RP-HPLC with ES-MS and ICP-MS rather difficult in the past. The application of a desolvation system avoids the formation of the interfering ions in the first place. In this study the Aridus system was tested. The sulfur detection limit of the used ICP-qMS in its standard mode could be improved by a factor 2000 to 50 ng S g⁻¹. But great care had to be taken regarding species independent quantification, the major advantage of ICP-MS, since the analyte transport of certain compounds such as methionine or arsenite to the ICP was affected by the desolvation system. However, sulfate was found to be a suitable calibrant for sulfur containing peptides such as phytochelatins. Hence, this method demonstrates for the first time, the potential to identify and quantify individual phytochelatins without phytochelatin standards. This is of importance, since no reliable and affordable phytochelatin standards are available, which would be necessary when molecular mass spectrometric methods would have been used solely. But a successful quantitative speciation analysis of free phytochelatins and their arsenite complexes was hampered due to peak broadening and more serious, the formation of arsenic-artefacts.