Dual-wavelength increased sensitivity spectrophotometric determination of small amounts of zinc (BE) with α,β,γ,δ-tetrakis (5-sulfothienyl) porphine

Abstract

A new water-soluble porphyrin, α, β, γ, δ-tetrakis (5-sulfothienyl) porphine [T(5-ST)P or H 2 P], was synthesized. T (5-ST) P is soluble in water and the solution is stable at all pH ranges. The formation of dimer, which is serious problem of sulfophenyl derivatives, is not observed even in acid solution. The Soret band of acidic reagent species (H4P2+) is well apart from that of zinc complex (Zn-P, λmax=428 nm, ϵ=41.7×104 cm-1 mol-1 dm3) and locates at longer-wavelength side (λmax =456 nm, ϵ=32.9×104 cm-1 mol-1 dm3) than those of the conventional water-soluble porphyrins. Based on this spectral properties, spectrophotometric method for 10-9 g/cm3 levels of zinc(II) ions was developed. In this method, the difference in the absorbance at the wavelength of maximum absorption of the zinc complex (428 nm) and that of the reagent (H4P2+, 456 nm) was determined. A recommended procedure: take a sample solution containing 03.0 μg of Zn2+ into a 50 cm3 beaker, add 0.5 cm3 of 10-4 mol dm-3 T(5-ST) P and HCl-CH3COONa-NaOH buffer solution (pH 5.011.0). Heat the mixture to boil for 15 min and allow to cool to room temperature. Then, adjust pH to 3.04.0 with 2 cm3 of CH3COOH-CH3COONa solution, dilute to 25 cm3 with water and measure the absorbance at 456 nm (H4P2+) and 428 nm (Zn-P), respectively, against water with 1 cm cells. The tolerance limits of diverse ions for the determination of 1.31 μg of Zn2+ were 1000 μg of Sr2+, Ba2+, and Mg2+, 100 μg of Ca2+, In3+, Ga3+, Pb2+, Ag+, VO2+, and VO2+, 10 μg of Ni2+, Al3+, Cr3+, Cd2+, Cu2+, Hg2+, Fe2+, and Sn2+ and 1 μg of Mn2+ and Co2+. The Sandell sensitivity for A =0.001 was 1.12×10-4 μg Zn2+ cm-2 and the coefficient of variation was 0.6 % for 1.31 μg/25 cm3 of Zn2+ (10 determinations). © 1983, The Japan Society for Analytical Chemistry. All rights reserved.