Columns disinfection

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. 

Chlorotrifluoromethyl aniline (no. 73.) was found in the sediment samples. This compound is used as a reactant with chloro-aniline (no. 72) in the preparation of 4,4 -dichloro-3-(trifluoromethyl)-carbanilide, a disinfectant. Two other related compounds also found in some of the sediments were chlorophenyl isocyanate (no. 74) and chloro(-trifluoromethyl)phenyl isocyanate (no. 75). This suggests that some of the 4,4 -dichloro-3-(trifluoromethyl)-carbanilide may, in fact, exist in the sediment extracts but is decomposed in the injection port of the gas chromatograph, since it is very doubtful that the easily hydrolyzable isocyanates exist as such in the sediments. To strengthen this hypothesis some 3,4,4 -trichlorocarbanilide [none of the 4,4 -dichloro-3-(trifluorome-thyl)-carbanilide was available] was analyzed by GCMS. The injection port temperature was 300°C. As expected, none of the parent compound eluted from the column. However, mass spectra were obtained for chlorophenyl isocyanate, dichlorophenyl isocyanate, chloroaniline, and dichloroaniline. The presence of the carbanilides themselves (no. 76, 77, 78) was confirmed with the help of HPLC and mass spectral identification. 

Influence of Hypochlorite on Parfait Columns. One potential use of the parfait method is the recovery of organic matter from drinking water. To test for the interaction of chlorine disinfectant with column components or eluents, the influence of 2 ppm of hypochlorite was assessed in an unspiked control column. Each eluate was assayed for hypochlorite by using the ferrous N,N-diethyl-p-phenylenediamine titrimetric method (12). No hypochlorite was detected. Each eluate was also analyzed by GC and found to be virtually identical to a blank column without hypochlorite run simultaneously. 

Detection limit. A sensitive chromatographic method was developed to measure sub-part-per-billion levels of the disinfectant by-products iodate (I03), chlorite (C I02 ), and bromate (BrOf) in drinking water. As the oxyhalides emerge from the column, they react with Br to make Brj, which is measured by its strong absorption at 267 nm. For example, each mole of bromate makes 3 mol of Br by the reaction BrOj" + 8Br + 6H+ —> 3Brj + 3H20. 

Initially, application of IC for the analysis of inorganic disinfection by-products using conductivity detection was based on low-capacity ion exchangers. Therefore, injection volume and ionic strength of the sample were strictly limited to avoid column overloading. Also, the removal of interfering ions, such as chloride and sulfate, was necessary. Unfortunately, these methods are not well suited for routine analysis at levels below 1 jxg/L because of the high cost of sample pretreatment, as well as the time spent on preconcentration and cleanup steps. 

The U.S. EPA Method 321.8 specifies the use of an anion-exchange column and detection of bromate using inductively coupled plasma-mass spectrometry (ICP-MS) in the atmospheric pressure mode. The U.S. EPA Method 326.0 has been developed for the analysis of ultra trace bromate concentrations in drinking water using a postcol-unm derivatization reaction with Mo(VI). A review of the methods of IC determination of inorganic disinfection byproducts published by U.S. EPA has been conducted by Hautman et al. The ISO standards for the determination of inorganic oxyhalides in water are smnmarized in Table 1, and U.S. EPA methods recommended are listed in Table 2. 

In 1993, the USEPA published Method 300.0—the first USEPA method widely accepted as the standard for common inorganic anions.Soon, this method was updated to include part B for the determination of bromate and other inorganic disinfection by-products using a modem high-capacity anion exchange column with carbonate/ bicarbonate eluent. 

Quite logically, new columns are developed to meet a real analytical need. Proliferation in the use of surfactants is a case in point Surfactants have both hydrophilic and hydrophobic centers and are widely used in many industries because of their abiUty to reduce surface tension. Anionic surfactants, classified as alkanesul-fonates, alkyl sulfates and alkylbenzenesulfonates, are commonly used in detergents, cleansing agents, cosmetics and hygienic products. Cationic surfactants are quaternary ammonium compounds, which are used in cosmetics, disinfectants, foam depressants, and textile softeners. Nonionic surfactants are also present in a... 

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