Direct Determination of Part-Per-Billion Levels of Volatile Organics in Water and Soil Samples Using Glow Discharge Mass Spectrometry

摘要

A low pressure glow discharge ion source has been constructed in our laboratory and interfaced with a quadrupole mass spectrometer for the direct monitoring of trace organic vapors in air. Important features of this ion source include a simple design, low cost, low maintenance, and the ability to sample air directly without the need for membranes, splitters, or capillary restrictors. Although the flow rate of air into the source is approximately 2 standard mL per second, the pressure within the ionization region is maintained at 200 mTorr which reduces interferences caused by the formation of water cluster ions. Furthermore, the high flow rate of air into the ion source provides a simple and convenient means of purging volatile organics from water or soil samples directly into the mass spectrometer without additional apparatus or extensive sample preparation. Early studies with this system indicate that low part-per-billion levels of volatile organics such as benzene or tri-chloroethylene can be quantitatively determined in water and soil samples either by monitoring headspace above a sample or by direct purging. Analysis time of 2-5 minutes provides a high throughput of 10 or more samples per hour. (ERA citation 13:036996)