Probe for label-free quantitative analysis in liquid chromatography/mass spectrometry

A technique for detecting ion suppression in LC/MS was developed by adding a specific concentration of a probe molecule to an LC mobile phase. The probe is sufficiently acidic and hydrophilic, such that the intensity of the protonated probe, as analyzed in a mass spectrometer, is expected to decrease much more than those of other analytes when ion suppression occurs. Thus, the potential occurrence of ion suppression is detected by monitoring the intensity of the protonated probe. However, the probe has been developed for limited conditions of the LC mobile phase used in proteomics. In this paper, we examine the probe's applicability to the experimental conditions used in pharmacokinetics and drug metabolism. Our results demonstrate that the probe can be used in mobile phases, in which the pH ranges from 1.8 to 6.7 and the organic solvent concentration ranges from 10 to 90%. Furthermore, the detection of ion suppression in the analysis of Omeprazole in human plasma was demonstrated by increasing the amount of the plasma in the sample solution.