Characterization of a Membrane Interface for Analysis of Air Samples Using Time-of-flight Mass Spectrometry

Abstract

In the present study, we constructed a membrane inlet assembly for selective permeation of volatile airborne organic compounds for subsequent analysis by time-of-flight mass spectrometry. The time-dependent diffusion of analytes through a 75 µm thick polydimethylsiloxane membrane was measured by monitoring the ion signal after a step change in the sample concentration. The results fit well to a non-steady-state permeation equation. The diffusion coefficient, response time, and sensitivity were determined experimentally for a range of polar (halogenated) and nonpolar (aromatic) compounds. We found that the response times for several volatile organic compounds were greatly influenced by the alkyl chain length as well as the size of the substituted halogen atoms. The detection limits for benzene, ethylbenzene, and 2-propanol were 0.2 ppm, 0.1 ppm, and 3.0 ppm by volume, respectively, with a linear dynamic range greater than three orders of magnitude. These results indicate that the membrane inlet/time-of-flight mass spectrometry technique will be useful for a wide range of applications, particularly for in situ environmental monitoring.

Development and Optimization of an External-Membrane Introduction Photoionization Mass Spectrometer for the Fast Analysis of (Polycyclic)Aromatic Compounds in Environmental and Process Waters

“…In the case of membrane failure, the transfer line acts as a security device and restricts the water flow into the MS. In addition, external membrane probes can be easily utilized for a wide variety of different mass spectrometers and are already applied in many publications. − However, external setups in combination with REMPI are not published yet.…”