chromium is soluble in alkaline to slightly acidic waters, whereas trivalent chromium is insoluble or only sparingly soluble under similar conditions. Effluent guidelines of the National Pollutant Elimination Discharge System sets ambient quality requirements for surface waters at 170 mg/l for Cr(III) and 50 g/l for Cr(VI). 1 The World Health Organization recommends that the potable-water concentration of Cr(VI) be less than 50 g/l. 2 The Resource Conservation and Recovery Act (RCRA) of 1976 (PL 94-580), which sets provisions for hazardous waste management, sets the limit for total chromium at 5 mg/l in soil leachates obtained by the toxicity characteristic leaching procedure. 3 The United States Environmental Protection Agency has recognized the difference in toxicity between trivalent and hexavalent forms of chromium and has proposed that the RCRA EP Toxicity test apply specifically to hexavalent chromium. 4,5 The toxicity, environmental mobility, facile redox chemistry, and regulatory issues associated with Cr(VI) make the detection and quantification of this species in environmental samples a major concern. [5][6][7][8][9][10][11][12][13][14] Many methods for the determination of Cr are known, with atomic absorption spectrometry the most commonly used technique. 7 Additional elemental and nuclear analytical methods that can be used to determine Cr include inductively coupled plasma -atomic emission spectrometry, x-ray fluorescence, charged-particle x-ray emission spectrometry, mass spectrometry, and neutron activation analysis. 7 However, these instrumental methods can only determine the total chromium. To obtain information on speciation, a method of separating the ionic species of Cr must be applied prior to detection. 15,16 Hexavalent chromium can be more directly measured using electroanalytical and spectrophotometric techniques. 7 Stripping voltammetry can be used to selectively analyze for Cr(VI) in the presence of Cr(III). 17 -19 A variety of spectrophotometric and colorimetric techniques have been devised for determination of Cr(VI). The most prevalent colorimetric method uses the selective reaction of Cr(VI) with 1,5-diphenylcarbazide (DPC) under acidic condi-