Analytical Sciences

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

Susumu KAWAKUBO,*1 Katsuhisa SHIMADA,*2 Yasutada SUZUKI,*3 and Kazuya HATTORI*4

*1 Interdisciplinary Graduate School of Medical and Engineering Science, University of Yamanashi, Takeda, Kofu 400-8511, Japan
*2 Aqualab Co., Ltd., 4-3-18 Shibazaki, Tachikawa, Tokyo 190-0023, Japan
*3 Center of Instrumental Analysis, University of Yamanashi, Takeda, Kofu 400-8511, Japan
*4 HATSUMEC Inc., 425-4 Rengeji, Kuwana 511-0845, Japan

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 for chromium(III), iron and copper, respectively.

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