High sensitivity in particle beam mass spectrometry with a non-volatile electrolyte

In the investigation of the anodic oxidation of triphenylamine (TPA) by electrochemistry/particle beam mass spectrometry (EC/PB/MS), the presence of a nonvolatile organic electrolyte tetrabutylammonium perchlorate (TBAP) caused a significant MS signal enhancement of the TPA.+ ion. The magnitude of the signal enhancement was ca. 35-fold and was observed in the presence of 10/1 excess of TBAP. While the mobile phase additives have been frequently used in PB/LC/MS analysis to enhance analyte signal, the use of a non-volatile surface-active organic salt as a mobile phase additive, to enhance the signal of a neutral analyte, has not been reported. The present work demonstrates that in addition to the well-known improved mass transport of the analyte through the PB interface, the presence of TBAP also contributes to the reduced fragmentation of the analyte molecular ion, TPA.+, in the EI ion source; this effect also contributes to the observed signal enhancement. This is the first report about the effect of the mobile phase additive on the EI mass spectrum of the analyte. In addition, it is demonstrated that the concentration ratio of TBAP/TPA plays a critical role in the signal enhancement process. Best linearity, sensitivity and reproducibility of the calibration curves are obtained by keeping the TBAP/TPA ratio constant near an optimum value during calibrations