Development of membrane extraction with a sorbent interface-micro gas chromatography system for field analysis

The commercially available portable gas chromatographs have a rather limite d scope of applications, typically allowing analysis of gaseous samples onl y, and having relatively poor sensitivity. Combination of those instruments with modern sampling/sample preparation techniques can remedy these proble ms. A Chrompack micro-CC system equipped with a thermal conductivity detect or has been coupled to membrane extraction with a sorbent interface (MESI). The sorbent trap has replaced the GC injector. The design of the trap was also modified in order to enhance the preconcentration of analytes. The use of a thin flat sheet membrane reduces the response time, and decreases the memory effect of the system. Rapid separation times were achieved, and the sensitivity was significantly improved. MESI enables semi-continuous monit oring of both gaseous and aqueous samples, owing to the selectivity of the membrane material. The system does not use moving parts, therefore being re liable. The sensitivity of the micro-CC system was increased by a factor of more than 100 by the addition of the MESI system, even with a preconcentra tion time as short as 1 min. Chloroform, having a concentration lower than 1 ppb, was detected in tap water. A cup system was used to allow headspace sampling of volatile organic compounds from aqueous matrices, keeping the m embrane away from interfering species that could be present in water, and i mproving the mass transfer. A linear calibration line was obtained, and the estimated limit of detection was 60 ppt. This represents a great improveme nt for the sensitivity of the micro-CC system. (C) 2000 Elsevier Science B. V. All rights reserved.