MEMBRANE EXTRACTION WITH A SORBENT INTERFACE FOR CAPILLARY GAS-CHROMATOGRAPHY

A new analytical method, combining the hollow fiber membrane, cryofocu sing, and thermal desorption technologies, has been developed to allow rapid routine analysis and long-term continuous monitoring of volatil e organic compounds in various environmental matrices. This method of membrane extraction with a sorbent interface (MESI) is simple, effecti ve, and solvent-free and easy to automate. It minimizes the loss of an alytes by interfacing the membrane extraction module directly to a cap illary gas chromatograph (GC). Application of hydrophobic membranes pr events moisture from entering the carrier gas. The sensitivity of the system is significantly enhanced with the cryogenic sorbent trap becau se of a high sample throughput. Experimentally, the MESI system consis ts of a hollow fiber membrane module, a cryofocusing and thermal desor ption sorbent interface, an isothermal capillary GC, and a computer. T he membrane is in direct contact with a sample or its headspace. Analy tes of interest diffuse across the membrane and are collected at the c ryogenic trap. A heat pulse desorbs all collected analytes at the trap and produces a:narrow concentration band at the front of the GC colum n. During the method development process, several designs of membrane modules were investigated, and their extraction performances were comp ared. At the optimum experimental conditions, the limit of detection f or trichloroethene in water was 1 mu g/L, and a RSD below 3% was achie ved using a flame ionization detector. The detection limit for the sam e analyte obtained with the conventional purge-and-trap followed by GC /MS is typically 0.2 mu g/L. Parameters influencing the sensitivity an d precision of the MESI system were studied. Quantitative extraction w as performed to improve accuracy of the analysis without the need for internal standards. A number of environmental applications were demons trated, which included analysis of VOC contaminants in clean water, wa stewater, and laboratory air.