Visual Determination of Trace Zinc(II) by Reverse Phased TLC with Tetrakis(4-carboxyphenyl)porphine

Abstract

A new visual colorimetric and fluorimetric determination of trace zinc(II) has been developed by thin-layer chromatography (TLC) with tetrakis(4-carboxyphenyl)porphine (TCPP). In this method, the spots that are dependent on each metal ion concentration of zinc(II), copper(II), cadmium(II), and mercury(II) appear selectively on an octadecylsilanized (ODS) silica thin layer by chromatographic separation with 90% (w/w) methanol. The yellow-colored zinc(II)-TCPP complex is distinguished visually from the other species with different colors. The zinc(II) concentration is determined by a visual comparison of the yellow-colored spot. The visual detection limit is 3 × 10−6 mol dm−3, defined as the minimum concentration that is visually distinguishable against a reagent blank. The calibration curve assessed with the densitometric responses is linear in the concentration range 0∼5 × 10−6 mol dm−3. The detection limit, which is calculated with 3 σ at the reagent blank, is 3 × 10−7 mol dm−3. On the other hand, the fluorimetric detection of the zinc(II)-TCPP complex is also available under the irradiation of UV light in the dark, and the visual detection limits is 8 × 10−7 mol dm−3. The calibration curve in the fluorimetric mode is linear in the concentration range 0∼3 × 10−6 mol dm−3, and the limit of detection is 3 × 10−7 mol dm−3. The effect for the determination of zinc(II) is not found in the presence of magnesium(II), aluminum(III), calcium(II), chromium(III), iron(III), nickel(II), and cadmium(II). The proposed method has been successfully applied to the determination of zinc(II) in river-water samples around an old mine.