Trihalomethanes

Trihalomethanes (TTHMs) are organic chemicals that contain one carbon atom, one hydrogen atom, and three halogen atoms. The most common trihalomethanes found in water are trichloromethane (chloroform), bromodichloromethane, dibromochlo-romethane, and tribromoethane (bromoform). Chloroform is found in the highest concentrations. It is formed by the reaction of free chlorine with certain natural organic compounds in the water. 

The primary drinking water regulations provide an MCL of 0.10 mg L-1 for total trihalomethanes. Recently, public water suppliers have switched from the use of chlorine as a water disinfectant to the use of chloroammines. The latter limits the formation of trihalomethanes, but it could be very toxic to aquatic organisms. 

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Dihalocarbenes are formed when trihalomethanes are treated with a strong base such as potassium tert butoxide The trihalomethyl anion produced on proton abstraction dissociates to a dihalocarbene and a halide anion... 

This IS called the haloform reaction because the trihalomethane produced is chloroform (CHCI3) bromoform (CHBrj) or iodoform (CHI3) depending on the halogen used... 

Methyl ketones are cleaved on re action with excess halogen in the presence of base The products are a trihalomethane (haloform) and a carboxylate salt... 

The Analysis of Trihalomethanes in Drinking Water by Liquid Extraction US Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, OH, 9 Sept. 1977. 

Although each gas chromatographic method has its own unique considerations, the following description of the determination of trihalomethanes in drinking water provides an instructive example of a typical procedure. 

Procedure. Samples are collected in 40-mL vials with screw-caps lined with a Teflon septum. Fill the vial to overflowing, ensuring that there are no air bubbles. Add a reducing agent of ascorbic acid (25 mg/40 mL) to quench the further production of trihalomethanes, and seal the vial. Store samples at 4 °C, and analyze within 14 days. 

Prepare a single multicomponent working standard from the stock standards by making appropriate dilutions with methanol. Concentrations in the working standards should be at such a level that a 20- xL sample added to 100 mL of water gives a calibration standard whose response for each trihalomethane is within 25% of that for the samples to be analyzed. 

This method uses a short, packed column that generally produces a poor resolution of chromatographic peaks. The liquid-liquid extraction used to extract the trihalomethanes is nonselective. Besides the trihalomethanes, a wide range of nonpolar and polar organic constituents, such as benzene and... 

A sample blank of trihalomethane-free water can be kept with the samples at all times. If the sample blank shows no evidence for chloroform, then we can safely assume that the samples also are free from contamination. 

Due to the volatility of trihalomethanes, the presence of a headspace allows for the possible loss of analyte. 

Accuracy The accuracy of a gas chromatographic method varies substantially from sample to sample. For routine samples, accuracies of 1-5% are common. For analytes present at very low concentration levels, for samples with complex matrices, or for samples requiring significant processing before analysis, accuracy may be substantially poorer. In the analysis for trihalomethanes described in Method 12.1, for example, determinate errors as large as +25% are possible. ... 

Graham, R. C. Robertson, J. K. Analysis of Trihalomethanes in Soft Drinks, /. Chem. Educ. 1988, 65, 735-737. Trihalomethanes are extracted from soft drinks using a liquid-liquid extraction with pentane. Samples are analyzed using a packed column containing 20% OV-101 on 80/100 mesh Gaschrom Q equipped with an electron capture detector. 

Method f2.i describes the analysis of the trihalomethanes CHCI3, CHBr3, CHChBr, and CHClBr2 in drinking water using a packed column with a nonpolar stationary phase. Predict the order in which these four trihalomethanes will elute. 

The analysis of trihalomethanes in drinking water is described in Method f2.i. A single standard gives the following results when carried through the described procedure. 

Trihalomethane (ppb) Peak Area solution of terpene hydrate in a 25-mL volumetric flask and... 

Analysis of water from a drinking fountain gives areas of f.56 X i0 5.f3 X i0 f.49 X fOk and f.76 X fO- for GHGI3, GHGl2Br, GHGlBr2, and GHBr3, respectively. Determine the concentration of each of the trihalomethanes in the sample of water. 

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. 

Trihalomethanes in Drinking Water (Sampling Analysis, Monitoring and Compliance), U.S. Envkonmental Piotection Agency, EPA/570/9-83-002, Washington, D.C., 1983. 

Suzuki, Y., Koizumi, A. and Takeuchi, Y., Adsorption of trihalomethane from... 

Total Trihalomethanes none 0.10 Liver, kidney or central nervous Byproduct of drinking water disinfection... 

AC filtration does remove some organic chemicals that can be harmful if present in quantities above the EPA Health Advisory Level (HAL). Included in this category are trihalomethanes (THM), pesticides, industrial solvents (halogenated... 

Brewing Potable water treatment Removal of trihalomethanes (THM) and phenolics... 

Under drinking water plant treatment conditions, humic materials and/ or resorcinol do not produce trihalomethanes with chlorine dioxide even when a slight excess of chlorine (1 percent to 2 percent) is present. Also, saturated aliphatic compounds are not reactive with chlorine dioxide. Alcohols are oxidized to the corresponding acids. 

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