2006 Volume 55 Issue 10 Pages 781-786
The flow injection analysis of a trace amount of chromium ion was investigated by an on-line concentration method using a Teflon filter tube. 1,5-Diphenylcarbazide was used as a detection reagent for the spectrophotometric determination of Cr(VI). Cr(VI) was coprecipitated with aluminum hydroxide in a reaction coil at pH 8.0∼8.5; then, the coprecipitate of Cr(VI) and Al(III) was collected with a filter tube by concentration for 5 min at a sample flow rate of 2 ml/min. The precipitate collected was eluted with 1 M HNO3 as a carrier solution. The Cr(VI) was determined on-line by monitoring at 542 nm. When Al(III) was used as a precipitant, the limit of detection and the lower limit of determination for Cr(VI) were 0.08 and 0.25 ppb, respectively. The relative standard deviation (RSD) for 30 ppb Cr(VI) was 0.3% (n = 7). On the other hand, Pb(II) was used as a precipitant; then, a calibration curve constructed by 60 min concentration for Cr(VI) was linear over the range 0 to 50 ppb. The limits of detection and determination for chromium were 0.004 and 0.013 ppb, respectively. The RSD for 2 ppb Cr(VI) was 1.0% (n = 7). The proposed method was applied to the determination of river water samples. As a result, the chromium in the natural water samples examined was below the detection limit (0.004 ppb). The proposed FIA system could afford a simple and rapid analysis of Cr(VI) in natural water samples.
