Oxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV): an ultra-high sensitivity spectrophotometric reagent for hydrogen peroxide

Abstract

The water-soluble titanium(IV)–porphyrin complex, oxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV)[TiO(tpyH₄)⁴⁺], was found to enhance the spectrophotometric determination of trace amounts of hydrogen peroxide. A 0.05 mol dm^–3 hydrochloric acid solution containing TiO(tpypH₄)⁴⁺ was used (the Ti—TPyP reagent), the absorbance of which decreased at 432 nm as hydrogen peroxide was added. This was due to the consumption of the TiO(tpypH₄)⁴⁺ complex following the formation of peroxo[5, 10, 15, 20-tetra(4-pyridyl)porphyrinato]titanium(IV). The decrease in absorbance at 432 nm (ΔA₄₃₂) was proportional to the concentration of hydrogen peroxide, from 1.0 × 10^–8 to 2.8 × 10^–6 mol dm^–3, in the sample solution (25 pmol–7.0 nmol per assay). The reaction was accelerated by hydrogen ions; the presence of 1.6 mol dm^–3 perchloric acid was found to promote complexation to the greatest extent. A ΔA₄₃₂ of 1.9 × 10⁵ was found for 1 mol dm^–3 hydrogen peroxide. A measurement precision of 1.2% for 1.0 × 10^–6 mol dm^–3 hydrogen peroxide (n= 8) was obtained. The reagent can be used for the determination of hydrogen peroxide in water samples such as tap water and rainwater over the range from 1.05 × 10^–7 to 3.34 × 10^–5 mol dm^–3.