Rapid, high-sensitivity analysis of oxyhalides by non-suppressed ion chromatography-electrospray ionization-mass spectrometry: application to ClO4-, ClO3-, ClO2-, and BrO3- quantification during sunlight/chlorine advanced oxidation

A rapid and sensitive method is described for measuring perchlorate (ClO4-), chlorate (ClO3-), chlorite (ClO2-), bromate (BrO3-), and iodate (IO3-) ions in natural and treated waters using non-suppressed ion chromatography with electrospray ionization and tandem mass spectrometry (NS-IC-MS/MS). Major benefits of the NS-IC-MS/MS method include a short analysis time (12 minutes), low limits of quantification for BrO3-(0.10 mu g L-1), ClO4- (0.06 mu g L-1), ClO3- (0.80 mu g L-1), and ClO2-(0.40 mu g L-1), and compatibility with conventional LC-MS/MS instrumentation. Chromatographic separations were generally performed under isocratic conditions with a Thermo Scientific Dionex AS16 column, using a mobile phase of 20% 1 M aqueous methylamine and 80% acetonitrile. The isocratic method can also be optimized for IO3- analysis by including a gradient from the isocratic mobile phase to 100% 1 M aqueous methylamine. Four common anions (Cl-, Br-, SO42-, and HCO3-/CO32-), a natural organic matter isolate (Suwannee River NOM), and several real water samples were tested to examine influences of natural water constituents on oxyhalide detection. Only ClO2- quantification was significantly affected - by elevated chloride concentrations (>2 mM) and NOM. The method was successfully applied to quantify oxyhalides in natural waters, chlorinated tap water, and waters subjected to advanced oxidation by sunlight-driven photolysis of free available chlorine (sunlight/FAC). Sunlight/FAC treatment of NOM-free waters containing 200 mu g L-1 Br(-)resulted in formation of up to 263 +/- 35 mu g L(-1)and 764 +/- 54 mu g L-1ClO3-, and up to 20.1 +/- 1.0 mu g L-1 and 33.8 +/- 1.0 mu g L-1BrO3- (at pH 6 and 8, respectively). NOM strongly inhibited ClO3- and BrO3- formation, likely by scavenging reactive oxygen or halogen species. As prior work shows that the greatest benefits in applying the sunlight/FAC process for purposes of improving disinfection of chlorine-resistant microorganisms are realized in waters with lower DOC levels and higher pH, it may therefore be desirable to limit potential applications to waters containing moderate DOC concentrations (e.g., similar to 1-2 mg(C) L-1), low Br(-)concentrations (e.g., <50 mu g L-1), and circumneutral to moderately alkaline pH (e.g., pH 7-8) to strike a balance between maximizing microbial inactivation while minimizing formation of oxyhalides and other disinfection byproducts.