Purge drinking water analysis

Reding, R. Kollman, W.B. Weisner, M.J. Brass, H.J., "Trihalomethanes in Drinking Water Analysis by Liquid-Liquid Extraction and a Comparison to Purge and Trap", Measurement of Organic Pollutants in Water and Wastewater, ASTM STP 686, C.E. Van Hall, Ed., American Society for Testing and Materials, Philadelphia, PA, 1979, pp. 36-41. 

Environmental Analysis One of the most important environmental applications of gas chromatography is for the analysis of numerous organic pollutants in air, water, and wastewater. The analysis of volatile organics in drinking water, for example, is accomplished by a purge and trap, followed by their separation on a capillary column with a nonpolar stationary phase. A flame ionization, electron capture, or... 

Trihalomethanes. Wherever chlorine is used as a disinfectant in drinking-water treatment, trihalomethanes (THMs) generaUy are present in the finished water. The THMs usuaUy formed are trichloromethane (chloroform), bromodichloromethane, dibromochloromethane, and tribromomethane (bromoform). There are four main techniques for the analysis of THMs headspace, Hquid— Hquid extraction (Ue), adsorption—elution (purge—trap), and direct aqueous injection. The final step in each technique involves separation by gas—Hquid chromatography with a 2 mm ID coUed glass column containing 10 wt % squalene on chromosorb-W-AW (149—177 p.m (80—100 mesh)) with detection generaUy by electron capture. 

We mentioned in Chapter 2 (Section 2.6.1) that a purge-and-trap procedure sometimes precedes an analysis by gas chromatography. An example of this procedure is found in the City of Lincoln, Nebraska, Water Treatment Plant Laboratory. Water treatment includes chlorination. When water is chlorinated, chlorine reacts with organic matter to form trihalomethanes (THMs), such as chloroform, bromoform, bromodichloromethane, and chlorod-ibromomethane. THMs in water are regulated by the Safe Drinking Water Act, and so the laboratory must analyze the treated water to determine their concentration. 

Analysis of Trihalomethanes in Drinking Water by the Purge and Trap Method... 

Several special sampling techniques should be mentioned. Many analyses are simplified by taking a sample from the vapor over the liquid sample. This procedure is known as headspace analysis.61 Another method known as purge-and-trap is used to concentrate a sample to improve detection limits. It is very popular in pesticide residue and drinking water analyses. 

Xylenes in drinking water, wastewaters, soils, and hazardous wastes may be analyzed by EPA analytical procedures (Methods 501, 602, 524, 624, 1624, 8020, and 8240) (U.S. EPA 1992 1997). These methods involve concentration of the analytes by purging and trapping over suitable adsorbent columns before their GC or GC/MS analyses. The primary characteristic ion for GC/MS identification (by electron-impact ionization) is 106, which characterizes ethylbenzene as well. Photoionization and flame ionization detectors are, in general, suitable for ppb- andppm-level GC analysis, respectively. Air analysis may be done by NIOSH Method 1501 (see Section 26.2). 

Supelco. Improved purge-trap-GC analysis of volatiles in drinking water by USEPA Method 524.2, Supelco Application. Note Supelco-012, 1997. 

Schnable, J.G. Dussert, B. Suffet, I.H. and Herzt, C.D. Comparison of quarter-hourly on-line dynamic head-space analysis to purge-and-trap analysis of varying volatile organic compounds in drinking water sources. Journal of Chromatography 1990, 513, 47-54. 

Chlorine and chlorine dioxide are other oxidizing agents that may be present in drinking water along with iron (III). Their interference can be removed by purging with nitrogen (for chlorine dioxide) or treatment with sodium oxalate (for chlorine) before analysis for iron (III). Nitrite can be decomposed with ammonium chloride in feebly acidic medium. 

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