DETERMINATION OF CHROMIUM(III) WITH ERIOCHROME CYANINE-R BY 4TH-DERIVATIVE SPECTROPHOTOMETRY

A fourth-derivative spectrophotometric determination of chromium (III) with Eriochrome Cyanine R (ECR) was described. The method was based o n measuring the fourth-derivative value (D-4) at 545 nm. The experimen tal and instrumental variables (wavelength range, scan speed, band wid th and order of derivative) were optimized. Under the optimum conditio ns, the calibration graph fit the equation d(4)A/d(4) = 3.75 x 10(5) [ Cr(III)] + 0.003 (r=0.9991) and have a relative standard deviation of 1.19%. The method was valid for concentration between 20 ng/ml and 80 ng/ml of chromium (III). The molar ratio of the formed complex was 1:2 (M:L). The proposed method was successfully applied to determination of chromium in steel.