Ozone modulation of volatile hydrocarbons using membrane introduction mass spectrometry.

A new method that we describe as chemical modulation of volatile hydrocarbons is investigated using ozonolysis pretreatment and membrane introduction mass spectrometry (MIMS). This extension to the MIMS technique is intended to enhance the selectivity of MIMS for measuring hydrocarbons in the complex mixtures often encountered in polluted air samples. The test samples for this study were dilute (parts per billion by volume, ppbv) two-component hydrocarbon mixtures in synthetic air. Ozone reacted to completely suppress the MIMS signal from beta-pinene in a mixture of toluene and beta-pinene and the MIMS signal from cyclohexene in a mixture of cyclohexene and cyclohexane. As expected, the ozone reaction produced little attenuation of the MIMS signal from toluene and cyclohexane in the test mixtures. The basis of the method is that the products of the ozonolysis, which is rapid for alkenes, are polar compounds that are excluded by the membrane used here, as confirmed in this study. Since the modulation only affects unsaturated hydrocarbons (and other similar organic compounds), the method can be used to aid in quantitative analysis of volatile hydrocarbon compounds in air samples for air pollution monitoring.