Evaluation of two different direct-sampling ion-trap mass-spectrometry methods for monitoring halocarbon compounds in air

Abstract

Two different direct-sampling ion-trap mass spectrometry (DSITMS) methods are evaluated for monitoring trace levels of volatile organic compounds (VOCs) in air. The first is based on the use of a sample introduction system that mixes the air sample into a helium stream prior to introduction into the ion trap through an open-split interface. The second utilizes a valve and uses zero air to flush the contents of the sample loop into the ion trap. Unique features of this system are its use of air in place of helium as a buffer gas for the ion trap, and the optimization of experimental parameters to maintain sensitivity and unit mass resolution. Dichlorodifluoromethane (CFC12) and carbon tetrachloride (CCl₄) were employed as test compounds for this study. Figures of merit for both sample introduction methods were comparable. Detection limits were approximately 50 parts per billion by volume in MS, selected ion monitoring (SIM), and MS/MS modes. Analysis speeds were on the order of 20 s or less per sample. The sensitivity of the ion trap, inherent selectivity of MS/MS, and fast response times of these sample introduction systems make these DSITMS techniques suitable for many applications that require on-line, real-time monitoring of VOCs in air. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 14–30, 2000