A Rapid and Simple Analytical Method for Cyanogen Chloride and Cyanogen Bromide in Drinking Water

-A simple gas chromatographic method was developed for the determination of cyanogen chloride and cyanogen bromide in drinking waters. Saturated headspace is injected directly onto a capillary column and the analytes are quantified by electron capture detection. Method detection limits are 0.04 and 0.2 #g/l for CNCI and CNBr, respectively. Effects of temperature and salt addition on analyte response were investigated. Other tests were conducted to determine the effects of sulfite and free chlorine on analyte stability. A concluding set of experiments showed the relationship between bromide concentration and cyanogen halide speciation. Key words--cyanogen chloride, cyanogen bromide, disinfection by-products, analytical method, sample preservation, suifite, chlorine, chloramines, bromide I N T R O D U C T I O N Since the 1970s there has been widespread concern in the U.S. over the presence of organic disinfection by-products (DBPs) in finished drinking waters. Due to the maximum contaminant level (MCL) set by the U.S. Environmental Protection Agency (U.S. EPA) for trihalomethanes (THMs) and the threat of future MCLs for other chlorination by-products, many water utilities are turning to ozone, chloramine and chlorine dioxide as a total or partial replacement for chlorine (McGuire, 1989). Chloramine is of particular interest, because it is inexpensive, provides a lasting residual, and it produces much lower levels of many DBPs. As a result, it is now used in 25% of U.S. utilities that serve more than 10,000 people (Regli, 1990). One concern over the widespread use of chloramines is the current level of uncertainty in the nature and health impacts of chloramine disinfection by-products. Much more information is needed before chloramines can be considered as a long-term replacement of chlorine. Cyanogen chloride (CNC1), a DBP listed in the U.S. EPA's first Drinking Water Priority List (U.S. EPA, 1988), is usually found in chloramined drinking water. The analytical method currently recommended by the EPA [method 524.2 (U.S. EPA, 1986)] for cyanogen chloride uses a purge and trap (P&T) and capillary gas chromatograph-mass spectrometer (GC-MS). Using this method, Flesch and Fair (1988) reported CNCI concentrations in field samples as well as data on the impacts of three different preservatives *Author to whom all correspondence should be addressed. for cyanogen chloride. Krasner et al. (1989) used a similar analytical approach (Krasner et al., 1990) to study the presence of cyanogen chloride and other DBPs in 35 water utilities across the U.S. Although the methods discussed above have been successfully used in exceptionally well-equipped laboratories, it is unlikely that most water utilities would have the specialized equipment to measure cyanogen chloride. The objective of this research was to develop an analytical method for cyanogen chloride that relies only on capillary GC, and does not require the use of purge and trap equipment, cryofocusing or the routine use of GC-MS. Considering the possibility of cyanogen bromide formation in waters high in bromide, analysis of this brominated analogue was also considered. E X P E R I M E N T A L M E T H O D S Preparation of aqueous standards Cyanogen chloride and cyanogen bromide primary stocks were prepared gravimetrically. In the case of CNCI, approx. 15 ml of the pure gas was transferred to a 40-ml (PTFEfaced) septum-capped vial containing 10mi of methanol. The exact amount of CNCI added was then determined by weight difference. These primary stocks were kept at -10°C. Secondary and tertiary stocks were prepared by diluting the primary stock with methanol and these were also stored at 10°C. Aqueous standards were obtained by volumetrically diluting the methanolic stocks into Super-Q w a t e r (Millipore Corp., Bedford, Mass., U.S.A.). Sample collection and headspace preparation All samples were gently poured into 40-ml vials and capped with PTFE-faced septa and screw caps headspacefree. The samples were then brought to 20°C and I0 ml of the sample volume was replaced with 10 ml of nitrogen. This was done by using a syringe (equipped with a stainless steel