Flow Injection Analysis of Oxalate in Foods Using Titanium(IV)-Porphyrin Reagent

Abstract

A rapid and sensitive flow injection analysis (FIA) with spectrophotometry detection by a Ti(IV)-porphyrin reagent is described for the determination of oxalate in foods using an immobilized oxalate oxidase reactor to yield hydrogen peroxide. The reagent is an aqueous solution of oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium(IV), TiO(tpypH₄)⁴⁺, which reacts with hydrogen peroxide to form a monoperoxo complex, TiO₂(tpypH₄)⁴⁺ having an absorption peak at 450 nm. The absorbance was proportional to the concentration of hydrogen peroxide. The flow-injection manifold comprised a two-channel system with an immobilized oxalate oxidase column. A linear relation was observed between the absorbance and the oxalate concentration ranging from 5×10^-7 to 2.5×10^-4 M (r=0.999), and 25 samples could be analyzed in one hour. The relative standard deviation for ten replicate measurements was 0.48% at 2.5×10^-5 M (500 pmol/injection). The application of this system for the determination of oxalate in foods gave satisfactory results. A good correlation (r=0.996) was seen between the results obtained by the proposed method and by the conventional method using a commercial F-kit.