The simple and rapid spectrophotometric determination of trace chromium(VI) after preconcentration as its colored complex on chitin

Preconcentration method with collection of metal complexes on a chitin has been applied to the spectrophotometric determination of chromium(VI) in water. The chromium(VI) is collected as its 1,5-diphenylcarbazide(DPC) complex on a column of chitin in the presence of dodecyl sulfate as counter-ion. The Cr-DPC complex retained on the chitin is eluted with a methanol-1 M acetic acid mixture (7:3, v/v), and the absorbance of the eluent is measured at 541 nm. Beer's law is obeyed over the concentration range of 0.05-0.6 mug of chromium(VI) in 1 ml of the eluent. The apparent molar absorptivity is 3.5x10(4) dm(3) mol(-1) cm(-1). The tolerance limits for Fe(III) is low, i.e. ten times that of chromium(VI), but some metal ions and common inorganic anions do not interfere in concentration range of 100-10 000 times that of chromium(VI). The present method can be applied to the determination of chromium(VI) in natural water samples.