Comparison of two validated gas-chromatographic methods for the determination of trihalomethanes in drinking water

In this paper the results obtained using two validated gas-chromatographic procedures on drinking water for the determination of trihalomethanes are compared. The volatile compounds, chloroform (CF), bromodichloromethane (BDCM), dibromochloromethane (DBCM) and bromoform (BF) were detected by purge and trap capillary column gas-chromatography with electrolytic conductivity detector ( ELCD) and the simple and rapid gas-chromatographic method by electron capture detector (ECD) after liquid-liquid extraction with n-pentane. For purge and trap ELCD method the response for the volatile compounds was linear for the concentrations of 0.5 to 40 µg/L. For liquid-liquid extraction ECD method the response was linear for the concentrations of 0.5 to 100 µg/L. The comparison of both methods was achieved by analyzing samples of drinking water collected in the city of São. Paulo, Brazil. The ratios of concentrations obtained by the two methods (ECD/ELCD) were as follows: l.l3 ± 0.9 for chloroform; 0.93 ± 0.15 for BDCM and 0.92 ± 0.17 for DBCM. Bromoform was not detected in the drinking water samples. The ratio of 1.08 ± 0.047 for total triahalomethane - THMt ( the sum of the three compounds) shows the equivalence of the compared methods.São comparados dois métodos cromatográficos validados para a determinação de trialometanos (clorofórmio, bromodiclorometano, dibromoclometano e bromofórmio) em água potável. Os métodos cromatográficos de fase gasosa, a saber: com detetor de captura de elétrons precedido de extração líquido-líquido e com detetor de condutibilidade eletrolítica com "purge and trap" foram comparados em termos de sensibilidade, precisão e recuperação. O estudo demonstrou que os resultados dos dois procedimentos são equivalentes apresentando as mesmas vantagens quando comparados