An On-Site Colorimetric Technique for Routine Determination of Chromium, Iron and Copper in Bath Solutions for Chromium(III) Conversion Coating

An on-site colorimetric technique was developed for the routine determination of chromium, iron and copper in bath solutions for the chromium(III) conversion coating. A portable colorimeter with a red-green-blue light emitting diode was used for the absorbance measurements. Iron and copper were determined as Fe(III)-thiocyanate and Cu(I)-bathocuproindisulfonate, respectively. Chromium(III) was determined simultaneously with iron or copper using green and blue light. A correction method of the matrix effect was proposed and its applicability was demonstrated. Analytical errors were within 500, 5 and 0.3 mg L(-1) hromium(III), iron and copper, respectively.