Mass spectrometric measurements of the negative ions formed in the thermionic ionization detector with nitrogen carrier gas

Abstract

A specialized ion source for an atmospheric pressure ionization mass spectrometer was constructed so that ionizing conditions within it were identical to those existing within the nitrogen carrier gas mode of the thermionic ionization detector for gas chromatography. During the passage of several substituted nitrobenzenes through this ion source, an effort was made to identify the negative ions which are thought to be responsible for this detector's response. For all compounds studied no negative ions having masses within the 1–500 a.m.u. mass range of the mass spectrometer were detected. However, negative ions of unknown masses greater than 500 a.m.u. were detected in each case. This unexpected result provides additional basis for speculation concerning the mechanism of response of the thermionic ionization with nitrogen mode.