Photometric Determination of Total Chromium in Waste Water from Chemical Laboratories by Binary Aqueous Phase Extraction

A definite amount of waste water sample was taken and fumed with an appropriate volume of HClO4 to oxidize Cr(Ⅲ) to Cr(Ⅵ).The solution containing Cr(Ⅵ) was adjusted to pH 5.0 with acetate buffer solution and reacted with diphenylcarbazide (DPC) solution to form a red colored coordination complex,which was extracted from the medium containing 15 mL of polyethylene glycol 6000 and 2.0 g of ammonium sulfate.The red colored coordination complex of Cr(Ⅵ) with DPC in the upper PEG phase,was separated from the lower aqueous phase and diluted to 25 mL in a volumetric flask,and its absorbance was measured at 540 nm.Interference of Fe(Ⅲ) was eliminated by adding 1 mL of H3PO4(1+1) to the test solution before adding the DPC solution.Tests for recovery were performed by standard addition method using sample solutions of waste water as matrixes.Values of recovery found were in the range of 98.7% to 104.0%.