Applications of membrane introduction mass spectrometry in on-line analysis of volatile organic compounds

Abstract

Membrane introduction mass spectrometry (MIMS) is a technique that combines the highly sensitive mass spectrometer to a membrane sample introduction system for enhanced performance. The fermentation of glucose with a genetically engineered yeast strain 1400 is monitored on-line using MIMS. A feedback control system is developed for automation of substrate addition and all operations including sampling, scanning, FIA control, calibration, and feedback control. This demonstrates that industrially important systems can be continuously monitored and process economy maximized. The combination of FIA with MIMS for analysis of environmentally important volatile organic compounds (VOCs) in seawater is examined and is compared to measurements made in water. The analyte responses are shown to be linear over several orders of magnitude, independent of seawater pH and independent of matrix effects for the VOCs studied. Investigation of the photolysis products of benzyl acetate and 3,5-dimethoxybenzyl acetate is performed on-line using MIMS. The reaction mixture is allowed to continuously flow through a silicone membrane into a triple quadrupole mass spectrometer for qualitative and quantitative analysis. The observed results prove that the relative reaction rates are dependent on the solvent and the photon intensity, and that the photolysis proceeds through both ion and radical pair mechanisms. MIMS is used to identify unstable free radicals in a reaction medium and to study their properties. In particular, aryldiazonium (C\sb6H\sb5N\sb2\sp+) and substituted (p-methoxy, m-chloro etc.) aryldiazonium and anilino radicals are generated by gas phase thermolysis and identified by measuring their ionization energies using ionization efficiency curves. Using this method, the ionization energy of the aryldiazonium radical is estimated as 7.68 $\pm$ 0.07 eV. Such a capability gives way for further mechanistic studies