DETERMINATION OF TRACE CHROMIUM(VI) IN WATER BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROPHOTOMETRY AFTER PRECONCENTRATION ON A SOLUBLE MEMBRANE-FILTER

A new method for the concentration and determination of <0.1 mu g/L of Cr(VI) in water by GFAAS is described. It is based on the formation o f a chromium(VI)-salicylfluorone (SAF)-tetradecylpyridinium(TDP) terna ry complex, the collection of the complex on a soluble membrane filter and the detection of the solution obtained after dissolving the membr ane and analyte in a proper solvent. The ternary complex [Cr(VI)-SAF-T DP = 1:2:2] is collected on a 0.45 mu m nitrocellulose filter. This is dissolved in a small volume of sulphuric acid and the chromium is det ermined by GFAAS under the optimized conditions. Good linearity is obs erved over the range 0.010-0.150 mu g Cr(VI) in 5.0 mL. The detection limit (three times the standard deviation of the blank) is 0.04 mu g/L with 50-fold preconcentration. No interference from ions normally pre sent in water was observed. The method has been applied to the concent ration and determination of Cr(VI) in water samples from several sourc es and the recoveries of added Cr(VI) were 91-101%.