PRECONCENTRATION AND DETERMINATION OF TRACE HEXAVALENT CHROMIUM[CR(VI)] IN WATER SAMPLES BY PRECIPITATE FLOTATION

The separative preconcentration of trace Cr(VI) in a water sample was studied by a precipitate flotation technique. After Cr(III), Al, Mg, and organic materials were removed by the pre-flotation with Fe(OH)3, trace Cr(VI) in 1.0 L of water sample was coprecipitated by the precipitation of AgCl in the solution of pH 8-9 adjusted with NaHCO3. All precipitates were floated by adding mixed surfactants, 1 : 1 solution of 0.5% sodium oleate and 0.5% sodium dodecyl sulfate ehtanolic solutions, and bubbling nitrogen gas. The floats were quantitatively collected on a micropore glass filter by suction and dissolved with conc. ammonia solution. The solution was marked to 25.00 mL with distilled water. Cr(VI) was determined by graphite furnace atomic absorption spectrophotometry. The results for seven determinations of one sample showed relatively good reproducibility with relative standard deviation of 9.71%. Recoveries were 86.0 and 91.0% for sample solutions in which 0.5 and 1.0 ng/mL Cr(VI) were spiked, respectively. The detection limit was improved about 20 times by this method.