A sensitive flow-based procedure for spectrophotometric speciation analysis of inorganic bromine in waters

Abstract

A flow-based system with solenoid micro-pumps and long path-length spectrophotometry for bromate and bromide determination in drinking water is proposed. The method is based on the formation of an unstable dye from the reaction between bromate, 2-(5-dibromo-2-pyridylazo)-5-(diethylamino)phenol (5-Br-PADAP) and thiocyanate ions. A multivariate optimization was carried out. A linear response was observed between 5.0 and 100µgL−1 BrO3− and the detection limit was estimated as 2.0µgL−1 (99.7% confidence level). The coefficient of variation (n=20) and sampling rate were estimated as 1.0% and 40 determinations per hour, respectively. Reagent consumption was estimated as 0.17µg of 5-Br-PADAP and 230μg of NaSCN per measurement, generating 6.0mL of waste. Bromide determination was carried out after UV-assisted conversion with K2S2O8 using 300µL of sample within the range 20–400µgL−1 Br−. The generated bromate was then determined by the proposed flow system. The results for tap and commercial mineral water samples agreed with those obtained with the reference procedure at the 95% confidence level. The proposed procedure is therefore a sensitive, environmentally friendly and reliable alternative for inorganic bromine speciation.