Instrument: 3100 Purge and Trap Sample Concentrator
Optimization of Method Parameters for the Evaluation of USEPA Method 524.2 Using a Purge and Trap with GC/MS
In this paper, an evaluation of different methods of moisture control will be presented and the Tekmar-Dohrmann 3100 Sample Concentrator will be optimized for the analysis of the USEPA 524.2 compound list using GC/MS.
This optimization of method parameters will focus on achieving the optimal chromatographic response by reducing the effect of water on the analysis.
Purge and Trap coupled with gas chromatography offers a simple method for the extraction and concentration of volatile organic compounds (VOCs) from multiple matrices such as waters and soils. USEPA Method 524.2 monitors a wide range of VOCs in drinking water. Due to the range and number of compounds analyzed in Method 524.2, there are several analytical problems that can arise. One of the most common problems involves the transfer of water to the analytical column. Excessive water transfer can cause problems with both the mass spectrometer and the chromatography. A mass spectrometer is especially sensitive to the presence of water. Various types of vacuum pumps may be incorporated (e.g., roughing pumps, turbomolecular pumps, diffusion pumps, etc.) and the pumping efficiencies can vary with time and with the level of maintenance. The pressure load that water imposes upon a mass spectrometer interferes with the efficiency of electron ionization, shortens the lifetime of the filaments, and results in higher maintenance costs. With respect to the chromatography, excess water often produces unacceptable broadening of early eluting peaks.
Removal of water can be facilitated through the use of hydrophobic trapping materials and incorporation of a moisture control system (MCS) which condenses water from the desorb gas during the transfer to the gas
chromatograph. The research described in this paper involves the evaluation of the moisture control system and two types of traps
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