Trace organic contaminant concentration by freezing—II: Inorganic aqueous solutions

Abstract

The presence of dissolved inorganic salts in aqueous solution impairs recovery efficiency of organic solutes by a freeze concentration procedure shown to be effective in the absence of salt. This effect is observed in the recovery of acetophenone and various phenols. Although previous tests demonstrated that mixing rate is not critical in the recovery of trace solutes by freeze concentration of distilled water solutions, it is important when dissolved salts are present. Higher mixing rates increase organic solute recovery. A relationship exists between salt content, mixing rate during the freezing process and organic solute recovery efficiency. Adjustment of sample pH becomes a factor in organic solute recovery. This is increasingly important as volume concentration ratio increases. Recovery is greater from acidic solutions. Freeze concentration of a complex mixture of phenolic materials showed no selectivity. All components were equally concentrated. This suggests the addition of a known quantity of an organic material to field samples as an internal reference. The reference would permit correction of results for losses induced by salt, inadequate mixing, etc. No effect on recovery is observed when iron, calcium, magnesium or copper is added to dilute organic aquesous solutions in excess of theoretical maximum coordination concentrations. Organometallic complexes, if they form, do not alter freeze concentration recovery efficiency. The advantages of combined freeze concentration and gas-liquid chromatographic analyses over conventional analytical procedures for separating and identifying complex mixtures of trace organics at less than 1 mg/l initial concentration is demonstrated with a mineralized industrial waste water.