ICPMS/MS with Benzene Vapor

Benzene vapor was introduced into the reaction cell of an inductively coupled plasma tandem mass spectrometer. By evaporating benzene into the helium supply of the octopole reaction cell, product ion spectra for plasma-based atomic and molecular ions were recorded. Based on these spectra, product ions for the separation of the atomic ions from spectral overlaps from isobaric or molecular ion interferents were selected. Background equivalent concentrations (BECs) or sensitivity ratios for analytes and interferents were compared to on-mass analyses without benzene addition. Depending on the analyte, up to 4 orders of magnitude improvement could be achieved. Specifically, the detection of S and Se could be improved substantially, and their BECs were reduced to the μg/L and ng/L ranges, respectively. The separation of isobaric Rb and Sr isotopes or of CeO⁺ from Gd⁺ was less effective with the use of benzene adducts alone. The separation could be substantially improved by using benzene and oxo or water adducts, and analyte/interferent sensitivity ratios greater than 10⁴ were obtained. Finally, the attenuation of ¹⁴N₂⁺, interfering with ²⁸Si⁺, was evaluated under dry plasma conditions. In this case, benzene could be used to lower the BEC for Si in both on-mass and mass-shift measurements by nearly 3 orders of magnitude.