Simultaneous spectrophotometric determination of chromium(VI) and iron(III) with chromogenic mixed reagents by H-point standard addition method and partial least squares regression

Simultaneous determination of Cr(VI) and Fe(III) by partial least squares (PLS) calibration and H-point standard addition method (HPSAM) is described. Mixed reagents of diphenylcarbazide and 1,10-phenanthroline in a non-ionic micellar solution of Triton X-100 was used as a selective chromogenic system for determination of Cr(VI) and Fe(III). The presence of a micellar system allows one to eliminate the previous solvent extraction step that is necessary for the determination of slightly soluble metal complexes in the absence of micelles. This reduces the cost and toxicity of the method. The total relative standard error for applying the PLS method to 15 synthetic samples in the ranges 0.20-6.00µgml-1 Cr(VI) and 0.20-8.00µgml-1 was 1.5%. The results of applying the H-point standard addition method showed that Cr(VI) and Fe(III) can be determined simultaneously with weight concentration ratios of Cr(VI) to Fe(III) varying from 15:1 to 1:30 in the mixed sample. Both proposed methods (PLS and HPSAM) were also successfully applied to the determination of Cr and Fe in several synthetic alloy solutions.