Triple Quad ICPMS (ICPQQQ) as a New Tool for Absolute Quantitative Proteomics and Phosphoproteomics

It is clear that sensitive and interference-free quantification of ICP-detectable elements naturally present in proteins will boost the role of ICPMS in proteomics. In this study, a completely new way of polyatomic interference removal in ICPMS for detection of sulfur (present in the majority of proteins as methionine or cysteine) and phosphorus (present in phosphorylated proteins) is presented. It is based on the concept of tandem mass spectrometry (QQQ) typically used in molecular MS. Briefly, the first quadrupole can be operated as 1 amu window band-pass mass filter to select target analyte ions (31P, 32S, and their on-mass polyatomic interferences). In this way, only selected ions enter the cell and react with O2, reducing the interferences produced by matrix ions as well as background noise. After optimization of the cell conditions, product ions formed for the targets, 47PO+ and 48SO+, could be detected with enhanced sensitivity and selectivity. The coupling to capillary HPLC allowed analysis of S- ...