Analytical Sciences

Cost-Effective Flow Cell for the Determination of Malachite Green and Leucomalachite Green at a Boron-Doped Diamond Thin-Film Electrode

Passapol NGAMUKOT,* Thiraporn CHAROENRAKS,* Orawon CHAILAPAKUL,* Shoji MOTOMIZU,** and Suchada CHUANUWATANAKUL*

*Sensor Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, Phayathai Road, Patumwan, Bangkok 10330, Thailand
**Department of Chemistry, Faculty of Science, Okayama University, Tsushimanaka 3-1-1, Okayama 700-8530, Japan

An electrooxidation and a cost-effective flow-based analysis of malachite green (MG) and leucomalachite green (LMG) were investigated at a boron-doped diamond thin-film (BDD) electrode. Cyclic voltammetry as a function of the pH of the supporting electrolyte solution was studied. Comparison experiments were performed with a glassy carbon electrode. A well-defined cyclic voltammogram, providing the highest peak current, was obtained when using phosphate buffer at pH 2. The potential sweep-rate dependence of MG and LMG oxidation (peak currents for 1 mM MG and LMG linearly proportional to v^1/2, within the range of 0.01 to 0.3 V/s) indicates that the oxidation current is a diffusion-controlled process on the BDD surface. In addition, hydrodynamic voltammetry and amperometric detection using the BDD electrode combined with a flow injection analysis system was also studied. A homemade flow cell was used, and the results were compared with a commercial flow cell. A detection potential of 0.85 V was selected when using a commercial flow cell, at which MG and LMG exhibited the highest signal-to-background ratios. For the homemade flow cell, a detection potential of 1.1 V was chosen because MG and LMG exhibited a steady response. The flow analysis results showed linear concentration ranges of 1 - 100 µM and 4 - 80 µM for MG and LMG, respectively. The detection limit for both compounds was 50 nM.

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