Determination of Bromate in the Presence of Brominated Haloacetic Acids by Ion Chromatography with Inductively Coupled Plasma Mass Spectrometric Detection

Abstract

Bromate is a disinfection by product (DBP) in drinking water that is formed during the ozonation of a source water containing bromide. Brominated haloacetic acids are DBPs that are anions at near-neutral pHs. The anion character of bromoacetic acid (pKa = 2.7) is similar to bromate, which causes the two species to coelute when NaOH is used as an eluent. Four columns are evaluated as a means of removing the potential false positives generated by bromoacetic acid. The alkyl quaternary amine based PA-100 guard column separates bromate from bromoacetic acid using 100 mM NaOH, but the analysis time is greater than 12 min. The use of 5 mM HNO3 as an eluent (with the PA-100) provides adequate separation of bromate from bromoacetic acid with an analysis time of less than 8 min. The stability of bromate in 5 mM HNO3 was evaluated using a DDI matrix (pH adjusted to 5.5, fortified with bromide) and a drinking water matrix (pH 4−9). The bromate recoveries in these two matrices were 93−105% with less than 4% RSDs. Tribromoacetic acid produces a broad peak that envelops the retention window of bromate. The tribromoacetic acid was removed using a reverse-phase sample pretreatment cartridge. The overall analysis procedure was evaluated in a synthetic chloride, sulfate, and nitrate matrix. In addition, precision and recovery data were collected from five ozonated drinking waters. The percent recoveries in the ozonated waters ranged from 90 to 98% with RSDs of less than 6%. The method detection limit for bromate is 0.8 μg/L.