LARGE-VOLUME INJECTIONS IN GAS-CHROMATOGRAPHY ATOMIC-EMISSION DETECTION - AN APPROACH FOR TRACE-LEVEL DETECTION IN WATER ANALYSIS

The ruggedness and analytical performance of on-line capillary gas chromatography-atomic emission detection (GC-AED) have been studied using 100-mu l injections of sample solutions in ethyl acetate, via a loop-type interface. A series of organophosphorus compounds were selected as test analytes; they were monitored using the carbon, sulphur, nitrogen, chlorine, bromine and phosphorus channels. The system showed no flame-outs or other maintenance problems even after 300 large-volume injections. The analytical potential of the system, expressed in terms of repeatability, linearity and minimum detectable amount, was not affected and a 100-fold increase in analyte detectability, in terms of concentration units, compared with a conventional 1-mu l injection was observed. As an application, GC-AED was combined off-line with solid-phase extraction. Several environmental contaminants were preconcentrated from river and tap water samples, and 20% (100 mu l) of the ethyl acetate eluent were directly analysed. With a sample volume of only 10 ml, the detection limits of the organophosphorus pesticides typically were ca. 0.1 mu g/l.