SOLID-PHASE EXTRACTION OF THE CHROMIUM(III)-DIPHENYLCARBAZONE COMPLEXPRIOR TO ION-PAIR CHROMATOGRAPHY AND APPLICATION TO GEOLOGICAL SAMPLES

A method for the pre-treatment of acid samples prior to ion chromatogr aphy is described. In a strong acid medium, Cr(VI) oxidizes diphenylca rbazide, the resulting products forming a stable complex which can be transferred in a methanolic medium by solid-phase extraction using pol yethylene as sorbent. This methanolic sample solution can be injected directly into a chromatographic system with a silica-based column. The separation and determination of the chromium complex can be performed by HPLC-using a mobile phase of 15% (v/v) acetonitrile containing 1 m mol/L tetrabutyl ammonium hydroxide (TBAH). The detection limit is est imated to be 2 mu g/L chromate and the linear range is at least 0.05-2 mg/L chromate.