Direct Sampling and Analysis of Volatile Organic Compounds in Air by Membrane Introduction and Glow Discharge Ion Trap Mass Spectrometry with Filtered Noise Fields

Abstract

Two direct air sampling interfaces have been evaluated in the laboratory for monitoring toxic air pollutants in real time by ion trap mass spectrometry in both single mass spectrometry and tandem mass spectrometry (MS/MS) modes. The mass spectrometer is the research-grade Finnigan MAT ion trap (ITMSTM) equipped with the Teledyne filtered noise field (FNF) module to eject unwanted ions and isolate only ions of interest. This results in enhanced sensitivity and selectivity for analyte ions of interest. MS/MS operation, for characterization of individual compounds with high sensitivity and specificity, is achieved by applying a supplementary RF signal to the end-caps of the ion trap. The direct air sampling interfaces are a semi-permeable helium-purged tubular membrane and an atmospheric sampling glow discharge ionization (ASGDI) source. Nonpolar and polar volatile organic compounds (VOCs) are measured at trace levels in air, using an environmental test chamber as the source of the target compound mixtures at known concentrations. Experiments conducted with the combination systems permit a comparison of the two direct air sampling interfaces for monitoring VOCs continuously in real time and illustrate the power of the FNF method to isolate ions with unit mass resolution and to perform MS/MS measurements.