Development of pulse introduction membrane extraction for analysis of volatile organic compounds in individual aqueous samples, and for continuous on-line monitoring

Most analytical applications of membrane extraction have involved continuous introduction of the sample into the membrane. In these studies, the measurements were made after membrane permeation reached a steady state. Since the diffusion of analytes in the aqueous matrix, and through the membrane is a slow process, it takes a certain amount of time to reach steady state. Any measurement made during the unsteady state period does not represent the true concentration of the sample stream. Furthermore, a relatively large sample volume is needed for the analysis because the sample has to be introduced continuously. Recently we have developed an alternative approach to membrane extraction referred to as pulse introduction membrane extraction (PIME). Here a pulse of sample is injected into the membrane, and steady state is not reached. This approach results in analytical system that has faster response and the capability to analyze individual samples. This concept can be used in conjunction with gas chromatography, mass spectrometry, as well as other analytical techniques. In this paper, the application of PIME for continuous monitoring of trace level organics in water is presented. The system demonstrated sub-ppb level detection limits, high precision and linear calibration curves. In this study, conditions for shorter analysis time and high sensitivity were studied. A comparison of PIME with steady state, continuous sample introduction is also presented. (C) 1998 Elsevier Science B.V. All rights reserved.