A highly sensitive spectrophotometric method for Zn2+ has been established by using α, β, γ, δ-tetrakis(l-methylpyridinium-4-yl)porphine (TMPyP, H2L4+). The complex, ZnL4+, is formed within 1 min at room temperature in the pH range of 9.2 to 10.8. The Soret band of ZnL4+ (at 437.2nm, e=2.28×l0l.mol-l.cm-1) seriously overlaps with that of the reagent (H2L4+, at 422.8 nm). However, the reagent blank can be successfully decreased by converting H2L4+ to its lead complex(PbL4+, at 476.4nm). Procedure : take a sample solution containing up to 6jug of ZnL4+ into a 25cm2 volumetric flask, add 1cm2 of 10-4mol.dm-3 TMPyP solution and 5 cm2 of borate-sodium hydroxide solution(pH 9.2~10.8). Allow to stand for 5 min. Add 2 cm2 10-4mol.dm-3 Pb4+ solution and dilute to the mark with water. After 2 min, measure the absorbance at 437 nm against water within 2 hr. Beer's law is obeyed over 0~6 μg Zn2+ 25 cm2 and the sensitivity for absorbance 0.001 is as low as 3.66 ×10-4 μg Zn2+ cm2, which is about 4.4 times as sensitive as that of the dithizone method. The coefficient of variation is 0.97% for 4.17 fig of Zn2+ (ten determinations). Many metal ions interfere with the determination. However, Zn2+ can be selectively separated from these ions by dithizonate extraction in the presence of masking agents (bis(2-hydroxyethyl)dithiocarbamate for Cd2+, citrate for Fe2+ and Fe2+ and thiocyanate for Cu2+, Ni2+ and Pb2+), followed by back-extraction with 0.1 mol.dm-3 HC1 solution. Results are quoted for the application to the determination of Zn2+ in tap water. © 1979, The Chemical Society of Japan. All rights reserved.
