Variables Influencing the Direct Determination of Haloacetic Acids in Water by Reversed-Phase Ion-Pair Chromatography with Indirect UV Detection

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Abstract
A reversed-phase ion-pair chromatographic system for the direct determination of haloacetic acids in water has been optimized utilizing indirect photometric detection. Acetic, chloroacetic, bromoacetic, iodoacetic, dichloroacetic and dibromoacetic acids were used to characterize the chromatographic system. The effect of temperature on retention time shows a non linear van't Hoff behavior indicating a change in the mechanism of retention at about 30°C. Above 30°C, retention times decreased proportionally to increases in the temperature of the column. Separations are achieved in the pH range of 3.5 to 6.3 with an optimum at ca. pH 5.4. Increases in the concentrations of KH2PO4, l-hexanesulfonate (competing ion) and acetonitrile result in proportional decreases in capacity factors with some selectivity variations depending on the analyte. Increases in the concentration of benzyltributylammonium ion (ion interaction reagent) resulted in increases in capacity factors with a usable range from 8 to 12 mM. Of the reversed phases studied, Spherisorb C-18 yielded the optimal results for the acids studied. Linear calibration curves for these acids were obtained utilizing indirect UV detection with detection limits as low as 2 parts per million.