MEMBRANE GAS-CHROMATOGRAPHIC SYSTEM FOR AUTOMATED EXTRACTION AND DETERMINATION OF TRACE ORGANICS IN AQUEOUS SAMPLES

A new automated extraction analysis system, which combines membrane cell technology with a pneumatically operated pressurized rotary gas chromatographic injection valve (POPSI), was developed and tested. The system was evaluated by using chlorinated aromatic compounds and pesticides as test sample mixtures. These compounds were successfully extracted and determined In water and organic/water type matrices In the part-per-trillion to part-per-billion range. Two modes of membrane operation were demonstrated: the continuous-flow mode, which produces concentration factors of ~3-5, and the stop-flow mode, which produces concentration factors of ~50-200. The effects of adding common organic solvents to the samples were examined and unexpected increases In extraction efficiency were observed. To reduce sample matrix effects, an internal standard procedure was evaluated. The Internal standard, which was added to the sample, was extracted with the analytes of Interest to help compensate for matrix effects. The accuracy and precision were significantly improved over the use of an external standard analysis; however, the Internal standard analysis was unable to completely compensate when high percent levels of organic solvents were added to the sample. Membrane/POPSI technology has potential both for use in sophisticated laboratory systems for automated extraction/analysis and also for simplified, dedicated systems for on-line analyzers. © 1990, American Chemical Society. All rights reserved.