On-line membrane extraction microtrap GC system for continuous monitoring of organic pollutants in air and water

A membrane sampling technique has been developed for continuous on-line monitoring of volatile organic compounds (VOCs) in water and in air. The VOCs can be sampled by passing the air/water continuously through a membrane hollow fiber. Organic pollutants selectively permeate through the membrane and are stripped by a flowing N₂ stream. The analytes are transferred to a microtrap, which is a microbore stainless steel tubing packed with a solid sorbent. The organics are trapped and concentrated in the microtrap. A pulse of electric current is used to heat the microtrap in a short time (0.8 approx. 1.2 sec.) to desorb the analytes as a concentration pulse which serves as an injection for GC separation. Continuous monitoring is accomplished by passing the air/water sample through the membrane and making microtrap injections at fixed intervals. Corresponding to each injection, a chromatogram is obtained. The system has detection limits at the ppb levels for most VOCs in both air and water. Linear calibration curves were obtained for both air and water. The advantages of membrane sampling is that it cab be fast, simple, and suitable for on line continuous monitoring.