STUDIES ON GAS-PHASE NEGATIVE-ION MOLECULE REACTIONS OF RELEVANCE TO ION MOBILITY SPECTROMETRY - MASS ANALYSIS AND ION IDENTIFICATION OF THE NEGATIVE REACTANT ION PEAK IN CLEAN-AIR

An understanding of the nature of the negative reactant ion peak (RIP) in an ion mobility spectrometer is a prerequisite to an understanding of the reactions that may occur in the presence of a pollutant. A study of the negative ions formed in ''clean'' air at atmospheric pressure together with a review of the literature has therefore been made. The use of isotopes and ''tuned'' mass analysis has enabled the identity of the majority of the ions to be determined with some confidence. The variations in relative ion abundance with water and CO2 concentration at four temperatures (25, 35, 45, 55-degrees-C) have been determined and the importance of CO2 concentration in determining the nature of the RIP in particular has been demonstrated. Radiolysis products formed in the air as it passes through the ionizing source have been shown to be of significance in the observed ion chemistry.