ULTRATRACE ANION ANALYSIS OF HIGH-PURITY WATER - A COLUMN COMPARISON

Several vendor columns were employed in a comparison of columns aimed at optimized separation and quantitation of ultratrace (i.e., high pg/ml to low ng/ml) levels of anions in high-purity water. The anionic profile of feed water will vary depending on the source; however, anions of most interest in high-purity water applications were chromatographed. The anions tested included fluoride, acetate, formate, chloride, nitrite, bromide, nitrate, phosphate, sulfate, and oxalate. Isocratic methods were used without exception and all separations were made under chemically suppressed conditions employing a Dionex AMMS-1 suppressor with 12.5 mM sulfuric acid as regenerant. All eluents were prepared from either sodium carbonate-sodium hydrogencarbonate or 50% (w/w) sodium hydroxide solution. Columns evaluated in this study included Dionex AS4A, AS9, and AS10, Sarasep AN1 and AN2, and Waters IC-PAK Anion HR. Comparisons were made on the basis of chloride retention, resolution of fluoride and acetate, column efficiency on nitrite and sulfate peaks, capacity, and run time. Column durability was not thought to be an issue because of the nature of the samples. Dionex AS10, Sarasep AN2 and Waters IC-Pak Anion HR columns were deemed acceptable though no single column met every requirement.