TRIHALOMETHANES DETECTION IN DRINKING WATER BY GAS CHROMATOGRAPHY (GC)

Abstract

The study was aimed for the identification and quantification of trihalomethanes in drinking water as THMs are highly carcinogenic even in ppb level. For the determination of trihalomethanes in drinking water by gas chromatography the samples were collected from Rawalpindi and Islamabad. Three different sampling sites were selected from Rawalpindi and three from Islamabad. Among the Rawalpindi city drinking water samples were collected from the areas of Westridge, Satellite town and Tench road. In Islamabad the samples were collected from F-7/3, E7 and F-8/1. Physical and chemical analysis of these water samples were done according to methods described in Standard Methods for the Examination of Water and Wastewater, e.g., temperature, pH, turbidity, conductivity, free chlorine, monochloroamines, dichloroamines, total chlorine, arsenic, fluoride, nitrates, TOC, sulphates, phosphates etc. Gas chromatographic method was developed to analyze the samples on GC instrument. Stock solutions for individual standard analytes of trihalomethanes (chloroform, dibromochloromethane, bromodichloromethane and bromoform) were prepared by dissolving them into methanol (GC grade). A temperature program was developed by hit and trial to get the finely isolated and well resolved peaks. Primarily liquid stock solutions of all four standard analytes were injected into the injector of GC. Retention times, peak areas and intensities of the standard analytes were calculated according to the known concentrations of standard analytes. To reduce the time of extraction and analysis the drinking water samples were subjected to SPME (solid-phase microextraction). CAR-PDMS SPME fibre was selected for this purpose. Reproducibility study of SPME fibre was done by analyzing stock solutions of standard analytes. The optimum extraction time for SPME fibre was selected by multiple analyses of standard analytes at 1, 5, 10 and 15 minutes. Maximum extraction was observed at 15 minutes and this extraction time was selected as optimum extraction time for the extraction of trihalomethanes at temperature of 250C. Samples for gas chromatographic analysis were collected in 40 mL glass chromatographic vials. Then the original water samples were analyzed according to the same GC programe as previously used for stock solutions of trihalomethanes. The actual depth of the SPME needle in the injection port linear was controlled. Quantification of the four analytes was performed using the peak area ratios of the analyte relative to the standard analytes based on single point calibration from stock solutions of standard analytes. Each standard was analyzed in duplicate. The concentrations of analytes were automatically calculated by relating to created calibration curves, where the peak area relationships were plotted as a function of concentration. Highest concentration, 774.97pg/L was found at consumer's house number 82 in F-8 sector of Islamabad and lowest concentration, 21.2gg/L was found at filtration plant Satellite town. Among 24 sampling sites of Rawalpindi and Islamabad only 3 sites were meeting the standard values and rest of 21 sites are exceeding the standard USEPA values.