Analysis of ppb levels of organics in water by means of purge-and-trap, capillary gas chromatography and selective detectors

The Environmental Protection Agency (EPA) has issued a series of methods (500 and 600 series) for the analysis of organics in drinking water and industrial discharges. Methods 601 and 602 employ packed-column gas chromatography (GC) with electrolytic conductivity (E1CD) and photoionization detection (PID), respectively. A purge-and-trap system is used for concentration of volatiles. The EPA is in the process of converting methods 601 and 602 and certain 500-series methods to capillary column analysis. We have also initiated the conversion of a number of these methods, using E1CD and PID and have described them in detail in this paper. We have evaluated both 0.32- and 0.53-mm diameter capillary columns, using helium and nitrogen as carrier gases with each detector. We found that with nitrogen optimum results are obtained at a flow-rate of 15 ml/min, and with helium at 6-8 ml/min. As a result of system optimization, including operation of the two detectors in series, and converting from packed to capillary columns, we found that analysis time could be reduced from 80 min (for two methods separately) to ca. 30 min. In addition, the elution of more than five components in one peak, observed when the packed column specified in method 601 are used, was eliminated.