Determination of Chromium(III) with Eriochrome Cyanine R by Fourth-Derivative Spectrophotometry

Summary

A fourth-derivative spectrophotometric determination of chromium(III) with Eriochrome Cyanine R (ECR) was described. The method was based on measuring the fourth-derivative value (D₄) at 545 nm. The experimental and instrumental variables (wavelength range, scan speed, band width and order of derivative) were optimized. Under the optimum conditions, the calibration graph fit the equation d⁴ A/d⁴ = 3.75 × 10⁵ [Cr(III)] + 0.003 (r=0.9991) and have a relative standard deviation of 1.19%. The method was valid for concentrations 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 the determination of chromium in steel.