Quantification of Dibromodimethylhydantoin Disinfectants in Water by Chemiluminescent Method
Hydantoin derived from imidazole is one of a class of organic heterocyclic compounds of five-membered ring structure composed of 3 carbon atoms and 2 nitrogen atoms at nonadjacent positions with dione form. Hydantoin and its derivatives are used in manufacturing pharmaceuticals, biocides, resins, preservatives and agrochemicals. 1,3-Dibromo-5,5-dimethylhydantoin (DBDMH), along with other halogenated derivatives such as 1-bromo-3-chloro-5,5dimethylhydantoin (BCDMH) and
... hloro-5,5dimethylhydantoin (DCDMH), are widely used as disinfectants in water treatment as well as in many other areas. 1,2 These compounds have low solubility in water, but ppm levels are enough to serve as a good disinfectant and bactericide as it slowly decomposes to produce free halogen in water. To monitor their effectiveness in water treatment and the residue after their applications, a rapid and sensitive method to examine their concentration in water is therefore needed. Although these agents have found widespread applications in industry due to their economic advantage, only limited research works have been done on their detection methods, especially on the methods suitable for detection of trace level of these chemicals. Dimethylhydantoin derivatives exhibit maximum absorption at around 210 nm; at such short wavelengths, UV detection may be interfered with relatively intense background signals, which could lead to unfavorable detection limits. Moreover, the UV absorption values can not reflect the decomposition of these compounds, as the major hydrolyzed product 5,5-dimethylhydantoin (DMH) also absorbs at a similar wavelength. 3 Chemiluminescent methods generally offer a lower detection limit and fast speed of analysis, especially when they are running in flow injection mode. In our recent study, it was found that DBDMH could react with humic acid in alkaline medium to emit light. This reaction was successfully applied to the flow injection CL determination of humic acid. 4 When the reaction was applied to the determination of DBDMH, however, the sensitivity was found to be surprisingly low (LOD was around 1 × 10 -6 mol dm -3 ). Determinations of BCDMH and DCDMH in swimming pool water by using luminol as the CL reagent were reported by Rao and coworkers. 3,5 These methods offer a moderate detection limit (about 1.0 × 10 -8 mol dm -3 ). In their systems, however, the analytes were injected into a mixed stream of luminol and H2O2, and this arrangement could deteriorate the detection limits and cause unnecessary reagent consumption as it is known that H2O2 could react with luminol in alkaline medium. Another issue seldom addressed in the quantification study was the instability of standards due to the hydrolysis of these halogenated hydantoins in aqueous solution. In CL detection method, it was found that the light emission intensity decreased with the increase of storage time of these halogenated hydantoins. Rao et al. measured the change of the CL intensity of BCDMH 3 and DCDMH 5 with time; the CL intensity of BCDMH and DCDMH both declined with time, the former declined 60% in 5 min and the latter declined 50% in 30 min. In this case, the accurate quantification of these compounds would be unlikely due to the instability of standards. Therefore the factor to affect the stability of these compounds was further investigated in this paper and we hoped to find at least a relative stable time window to allow the quantification to be carried out. N-Halo compounds including N-bromosuccinimide, chloramines T (N-chloro-p-toluenesulfonamide, sodium salt) and halogenated hydantoin derivatives have frequently been used as a source of free halogens. Their action in the CL reaction was often assumed to be the in situ formation of 327 ANALYTICAL SCIENCES MARCH Quantification of 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) was studied by its chemiluminescence (CL) reaction with luminol in an alkaline medium. The stability of DBDMH, 1,3-dichloro-5,5-dimethylhydantoin (DCDMH) and 1bromo-3-chloro-5,5-dimethylhydantoin (BCDMH) in water was initially assessed by its CL reaction capability. The results indicated that the hydrolysis process was critically dependent on the types of reagents and their pHs. Capillary electrophoresis (CE) separation with CL detection procedure was applied to the DBDMH solution. It was found that at least 3 species in the aqueous DBDMH solution could oxidize luminol to give luminescence: one of them was confirmed to be hypobromite and the others could be the unhydrolyzed or active oxygen produced in the hydrolysis reaction. Finally, a flow-injection chemiluminescent method was proposed for the determination of DBDMH. The concentration of the analyte showed a linear relationship with the CL intensity in the range of 1.2 × 10 -10 to 1.0 × 10 -6 mol dm -3 and the detection limit was as low as 6.2 × 10 -11 mol dm -3 . The relative standard deviation (RSD) is 1.7% (n = 9) for 2.8 × 10 -7 mol dm -3 DBDMH.