Facile and Sensitive Spectrophotometric Determination of Chromium

Abstract

A simple, sensitive, and selective spectrophotometric method is developed for the determination of trace amounts of chromium(VI) in various samples. The method is based on oxidation of 2,4-dinitrophenylhydrazine (DNPH) by chromium in an acidic medium and coupling with β-naphthol to give a red-colored dye, having an absorbance maximum at 663 nm, and/or coupling with α-naphthol to give a violet-colored dye, having an absorbance maximum at 503 nm. The method obeys Beer's law in the concentration range 0.02–4.0µg mL⁻¹ and 0.05–9.0 µg mL⁻¹, respectively. The optimum reaction conditions and other important analytical parameters were established. Interference caused by various nontarget ions was also investigated. The proposed method is applied to the analysis of chromium(VI) in environmental, pharmaceutical, and steel samples. The performance of the proposed method is evaluated using the student's t and F -tests.

Keywords:

• α-naphthol
• β-naphthol
• 2
• 4-dinitrophenylhydrazine (DNPH)
• chromium
• Spectrophotometry

The authors are thankful to DST and UGC for financial assistance through the FIST and SAP programs, respectively.

Notes

^a Can be masked up to 25 µg mL⁻¹ by the addition of 2 mL of 2% EDTA.

^b Can be masked up to 50 µg mL⁻¹ by the addition of 2 mL of 2% EDTA.

^a Mean ± SD (n = 5).

^b Tabulated t- value for 8 degrees of freedom at P (0.95) is 2.65 and tabulated F -value for (4, 4) degrees of freedom at P (0.95) is 5.72.

^c Gave no test for vanadium.

^d Chromoplex (Aristo Pharmaceuticals Ltd.). 0.550 g sample dissolved in 100 mL. Certified amount of chromium 200 µg. Tested for 2 µg mL⁻¹.

^e GKW Steel Ltd. (C, 0.54%; Mn, 0.89%; S, 0.018%; P, 0.034%; Si, 0.33%; Cr, 1.02%; V, 0.13%).

Certified amount of chromium taken *1.02 µg mL⁻¹ and **2.04 µg mL⁻¹.