QUANTITATIVE ANALYSIS OF DISINFECTION BY-PRODUCTS IN DRINKING WATER DISTRIBUTION NETWORK USING SPME AND GC

Abstract

Trihalomethanes (THMs) occurrence in the drinking water is a major concern in public health owing to their toxicological effects on health. These are formed during water disinfection process. This study aims at THMs monitoring in drinking water distribution network by gas chromatography with electron capture detector (GC-ECD) and TRB-1 column (30 m x 0.32 mm x 1 μm). The SPME fibre (75 μm CAR-PDMS) was found to be the most suitable for THMs extraction. A standard solution of each THM was prepared in methanol following EPA Method 551.1. Calibration of standards was carried out to obtain reproducible peaks and linear calibration curves. Response surface methodology and a central composite design (CCD) was employed for optimization of variables for THMs determination. The accuracy of the model was investigated by ANOVA. The results of RSM revealed that optimum conditions for THMs analysis were 30 min extraction time at 80 oC with addition of 3.25 g Na2SO4 salt and 8 min of desorption time. The optimized conditions were then used for quantification of THMs in water samples of NUST. The results achieved indicated presence of THMs in 90 % of drinking water samples collected after chlorination, with 30% sites exceeding the standard value of 80 μg/L. The most dominant THM recorded was dichlorobromomethane in almost 95 % of the samples. Iodoform was detected comparatively at low concentration (0.012 - 0.433 μg/L) in almost 45 % samples and in all the sites it was found within the threshold values (0.2 - 5 μg/L). It may be concluded that the HS-SPME technique has a great potential for the analysis of drinking water. These results show a strong link between concentration of UV254 absorbance and organic matter with THMs formation. The sites having high content of residual chlorine and UV254 exhibited comparatively larger peak signal for THMs. The potential reason for contamination at different points are due to natural organic matter and residual chlorine.