Speciation of common volatile halogenated disinfection by-products in tap water under different oxidising agents

Abstract

A simple and efficient method has been developed for the extraction and determination of sixteen common volatile halogenated disinfection by-products (DBPs) using the static headspace (HS) technique coupled with gas chromatography–mass spectrometry (GC–MS). The DBPs determined included trihalomethanes (THMs), halonitromethanes (HNMs) and haloacetonitriles (HANs). The extraction parameters (HS conditions, ionic strength and organic modifier) were studied in order to obtain the highest sensitivity. Under optimum conditions (water containing 250μL of methyl tert-butyl ether and 6g of anhydrous sodium sulphate was heated 20min at 80°C), the HS–GC–MS method provides limits of detection between 10 and 200ng/L and a relative standard deviation of ∼5.6%. Samples collected from genuine tap water treated with different oxidising agents (ClO2/Cl2, Cl2/NH2Cl and O3/Cl2) in several disinfection treatment plants were successfully analysed in order to establish their effect on the occurrence of DBPs. In parallel, the influence of the main parameters of the water (pH, conductivity, nitrite, nitrate, free residual chlorine, permanganate oxidability and bromide) was also studied. The results suggest that the permanganate oxidability (related to organic matter) and the bromide concentration as well as disinfection conditions are directly related to the occurrence of THMs, HNMs and HANs, both in their concentrations and speciation. The method developed was compared to the reference EPA Method 551.1 for the analysis of tap water.