Characterization of a membrane interface designed for analytical scale sample introduction into a mass spectrometer

A membrane interface has been constructed for analytical scale sample introduction into a mass spectrometer. The interface was designed to be easy to use while achieving the following two goals: (i) to improve the mass transport efficiency of the analyte from the sample solution to the mass spectrometer ion source and (ii) to improve performance while reducing the sample sizes utilized for routine direct analyses with membrane introduction mass spectrometry (MI/MS). In order to systematically characterize this interface, a variety of key mass transport parameters including membrane thickness, temperature, analyte flow rate, and pneumatic assist carrier gas flow rate have been examined. Interface characterization studies have focused primarily on two analytes, benzene and ethanol. These two analytes were chosen to compare the relative importance of each of the key mass transport parameters for the two most common applications of MI/MS, environmental analyses and fermentation monitoring. The results of these studies suggest that mass transport of the analyte from solution phase to the membrane (including the use of the thin layer approach), membrane dimensions and membrane temperature are among the more important factors affecting analyte response and limits of quantification. Other significant results suggest that, when given a warm unrestricted path from the membrane to the ion source, the permeation (flux) of water from the aqueous matrix may be a major factor affecting the mass transport of analyte from the membrane to the ion source of the mass spectrometer. The comparison of the effects of the key mass transport parameters for environmental analyses and fermentation monitoring shows that each of these two applications depend on a markedly different set of parameters for achieving optimal performance.