Trihalomethane detection

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. 

The absence of chromatographic separation makes MIMS a fast technique. It is advantageous in some applications where only select compounds are to be detected or the total concentration of a mixture is to be determined. For instance, the total concentration of trihalomethanes (THMs, including chloroform, bromoform, bromodichloromethane, and dibromo-chloromethane) in drinking water can be determined by MIMS in less than... 

Trihalomethanes, which are formed during chbrination, often occur at higher concentrations than many other organic components detectable by gas chromatography chloroform is frequently found at levels of 10-100 pg/L,... 

It is particular concern in the analysis of aqueous samples, because the solvent effects involved during the direct aqueous injection (DAI) allow the direct analysis of levels ()ig l) of trihalomethanes and related compounds in water, using well deactivated thick film columns and E(D detection [19, 20 ]. 

For the analysis of VOCs, the most common column is a 75 m X 0.53 mm i.d. DB-624 fused silica capillary with 3 pm film thickness. A typical DB-624 permits detection from vinyl chloride (bp= 13.9°C and solubility = 2700 g/L) up to 2-chloronaphthalene (bp = 256°C), being therefore suitable to determine a wide range of compounds of different volatilities and polarities. For specific applications, e.g., control of trihalomethanes in drinking water, a short column of 30 m can be used, and the analysis time is, of course, reduced. 

Other applications of P T are related to the control of trihalomethanes in finished drinking water. Fig. 2 shows a typical profile where chloroform, hromodichloromethane, dihromochloromethane, and bromoform were detected at 80-100 pg/L. The technique, when coupled to MS, can also be applied to identify compounds responsible for taste and odor problems in water. 

Results from a more limited study were recently reported by Kelly ( 3). Iowa scientists analyzed water samples from 128 wells involving 58 public water supplies between May 1984 and March 1985. One or more synthetic chemicals were found in 57 wells representing 33 water supplies. Trihalomethanes, as a group, were the most commonly occurring substances. The most frequently detected single product was atrazine, found in 24 wells. Overall, only 6, of 34 pesticides analyzed, were detected. None were above established standards or standards that could be set by methodology discussed later in this report. The highest level reported for any pesticide was 16.6 ppb for alachlor. 

Trihalomethanes 502.2 Purge and trap, GC-photoionization-electrolytic conductivity detection... 

In water, GC-MS is coupled to purge and trap or headspace sample preparation for the analysis of VOCs like BTEX and MTBE. Another important group of volatile analytes in water are DBFs. Attention has been directed to volatile chlorinated compounds such as trihalomethanes (THMs), as well as other semivolatile compounds such as haloacetic acids (HAAs), haloacetonitriles, haloketones, and ha-loaldehydes. The methods used to determine these compounds include GC-EI-LRMS, where a after derivatization step is necessary due to the low volatility and high polarity of these analytes. Using this technique, limits of detection were in the microgram per liter range. 

Environment Canada estimates that 100 to 150 g per year of 2,3,7,8-tetra-chlorodibenzodioxin and 2,000 to 3,000 g per year of 2,3,7,8-tetrachlorodibenzofuran are discharged in bleached pulp mill effluents (Phenicie, 1993). It is estimated that only 10 to 40% of small chlorinated organic compounds in bleached pulp mill effluents have been identified. Some of the other substances detected are chlorinated phenols, chlorinated acids, alcohols, aldehydes, ketones, sugars, aliphatic and aromatic hydrocarbons, trihalomethanes, chlorobenzenes, and aromatic thio ethers. Concentrations of individual chlorinated compound such as dichlorophenol, trichlorophenol, trichloroguaiacol, and tetrachloroguaiacol have been measured at 23%, 29%, 50%, and 95% of their respective LCjoS. 

Food chlorination is another source by which chlorinated and nonchlorinated organics enter the human body. Chlorine is used to treat cake flour to prevent crumbling on removal from the oven. It has been estimated that over 1.5% of the total flour production in the United Kingdom is chlorinated. Trihalomethanes have also been detected in human milk and serum. Levels detected are 0.30 0.032 /u,g/mL for human milk and 0.88 0.012 yag/ mL for the serum, thus showing the extensive burdens of these trihalomethanes in the human body. 

The extensive use of chlorine to purify water has recently been shown to result in the formation of chlorinated hydrocarbons. Low molecular weight compounds, such as the haloforms (HCX3), also called trihalomethanes (THM), are volatile and have been shown to be carcinogenic. They have been detected in drinking water and in the air of enclosed swimming pools. Thus, several alternate disinfectants (such as ozone, chlorine dioxide, UV, and ferrates) have been crmsidered as alternates to chlorine. Of these, the use of ozone has been most developed. 

L. Lepine and J. Archambault, Parts-per-trillion determination of trihalomethanes in water by purge and trap gas chromatography with electron capture detection. Anal. Chem. 64 810 (1992). 

The use of chlorine for disinfection of potable water has long been practised, it has recently been found [52, 54] that this can lead to a significant increase in the level of Trihalomethanes (THM). The important THM are chloroform, bromo-dichloromethane, chlorodibromomethane, and bromoform the levels detected range from 1 pg/1 to 100 pg/1 and above as total THM, of which typically 80% will be chloroform. THM arise from the chlorination of a number of precursors, many of them humic in nature. The bromine is believed to arise from bromide present in the water, which liberates bromine in the presence of excess chlorine. 

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