Determination of chromium (VI) by flow-injection spectrophotometry coupled with on-line microcolumn preconcentration

A rapid and sensitive method is described for flow-injection spectrophotometric determination of trace chromium (VI) in natural water. Preconcentration and elution of the trace analyte are achieved through quantitative and rapid adsorption on the surface of nanometer-size TiO₂ (anatase) powders and followed by the quantitative and reproducible elution of Cr(VI) using 2.0 M HCl as an eluent. The eluted Cr(VI) reacts with 1,5-diphenylcarbazide (DPCB) in the reaction coil to form a color complex, which is then detected by a spectrophotometer at the wavelength of 540 nm. The preconcentration factor is 55 for the sample volume of 25 mL, and the detection limit is 0.8 ng/mL Cr(VI). Under the optimized conditions, the analysis of Cr(VI) can be achieved at the rate of 6 samples/h for 0.001 μg/mL Cr(VI) or 20 samples/h for 0.1 μg/mL Cr(VI). The relative standard deviations are in the range of 0.37–3.35% (n = 5). © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 141–145, 1999