UV-visible spectral analysis for the characterization of the titanium(iv)-4-(2-pyridylazo)resorcinol complex as a reagent for determining hydrogen peroxide.

Titanium(iv)-4-(2-pyridylazo)resorcinol (Ti-PAR) has been effectively used for the determination of hydrogen peroxide. In 1985, Takamura et al. proposed its molecular structure showing the absorption peak at 508 nm. However the results obtained from computational calculations showed the absorption peak at 472 nm. Based on the UV-visible spectral simulations and crystal structures of metal-PAR registered in the Cambridge Structural Database (CSD), the structure of Ti-PAR-H2O2 showing the absorption peak at 508 nm was determined. Then the reaction profiles and the reaction mechanism were clarified.

Effect of photo-oxidation of on the determination of and using the - reagent.

The Ti-TPyP reagent, i.e. an acidic aqueous solution of oxo[5,10,15,20-tetra(4-pyridyl)-porphyrinato]titanium(iv) complex, denoted as TiO(tpyp), was developed as a highly sensitive reagent for determining hydrogen peroxide. The Ti-TPyP reagent exhibits a sharp absorption peak at 432 nm. Following the addition of hydrogen peroxide to the reagent, a new absorption peak appeared at 450 nm. Its absorbance was proportional to the hydrogen peroxide concentration with an apparent molar absorptivity of 1.1 × 105 L mol-1 cm-1. In the determination of hydrogen peroxide using the Ti-TPyP reagent, ascorbic acid concurrently present in the samples caused a positive error in the analytical results. In the present paper, the source of the error was revealed to be due to the production of hydrogen peroxide through the oxidation of ascorbic acid by singlet oxygen arising from the energy transfer between the dissolved oxygen molecule and the photo-excited porphyrin moiety of the TiO(tpyp) complex. The reaction mechanism was proposed for the photo-oxidation of ascorbic acid caused by the TiO(tpyp) complex to produce dehydroascorbic acid and hydrogen peroxide. The effect of ascorbic acid is really a serious problem in the practical uses of the Ti-TPyP reagent in food and biochemical analysis. However, use of ascorbic acid oxidase as a scavenger for ascorbic acid was found to be quite effective to remove its effect in the flow injection analysis of 3-hydroxybutyric acid in human serum.

Ultraviolet-visible spectral analysis for the reaction of hydrogen peroxide with a titanium(IV)-porphyrin reagent.

A Ti-TPyP reagent, i.e., an acidic aqueous solution of oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium(IV) complex, TiO(tpyp), was developed as a highly sensitive and selective spectrophotometric reagent for the determination of traces of hydrogen peroxide. The reagent exhibited a single absorption peak at 432 nm, and the addition of hydrogen peroxide to the reagent gave rise to a new peak at 450 nm, with height being proportional to the added hydrogen peroxide concentration. Recently we succeeded in clarifying the reaction specificity of the TiO(tpyp) complex to hydrogen peroxide from the viewpoint of the reaction mechanisms and molecular orbitals based on ab initio calculations. In the present study, we performed ultraviolet-visible (UV-Vis) spectral simulations for individual species in the proposed reaction mechanisms based on the theoretical calculations carried out using the Zerner's intermediate neglect of differential overlap (ZINDO) method, since the assignment of the observed absorption peaks to the respective reaction species is important to confirm the reliability of the analysis of hydrogen peroxide using the Ti-TPyP reagent. The absorption peaks at 432 nm and 450 nm were assigned to a H(2)O-adduct structure of the protonated TiO(tpyp) complex and the important structure corresponding to the monoperoxo TiO(tpyp) complex, respectively, under acidic conditions. Particularly, it should be noted that the addition of water molecules to the protonated TiO(tpyp) complex affects the maximum absorption wavelength appreciably. Taking the addition of water molecules to the complex into consideration, the reaction mechanism proposed previously was revised in this study. The results should contribute to providing a new way to evaluate analytical reagents.

Reaction specificity of a titanium(IV)-porphyrin complex to hydrogen peroxide in view of an Ab initio study.

A Ti-TPyP reagent, i.e. an acidic aqueous solution of oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium(IV) complex, TiO(tpyp), was previously developed as a highly sensitive and specific reagent for determining hydrogen peroxide. In the present work, the reaction specificity of the TiO(tpyp) complex to hydrogen peroxide was clarified based on ab initio calculations. The results provide a well-grounded argument for determining hydrogen peroxide using the Ti-TPyP reagent experimentally.

Characterization of a titanium(IV)-porphyrin complex as a highly sensitive and selective reagent for the determination of hydrogen peroxide: a computational chemistry approach and a critical review.

The Ti-TPyP reagent, i.e. an acidic aqueous solution of the oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato] titanium(IV) complex, TiO(tpyp), was developed as a highly sensitive and selective spectrophotometric reagent for determination of traces of hydrogen peroxide. Using this reagent, determination of hydrogen peroxide was performed by flow-injection analysis with a detection limit of 0.5 pmol per test. The method was actually applied to determination of several constituents of foods, human blood, and urine mediated by appropriate oxidase enzymes. The reaction specificity of the TiO(tpyp) complex for hydrogen peroxide was clarified from the viewpoint of the reaction mechanisms and molecular orbitals based on ab initio calculations. The results provided a well-grounded argument for determination of hydrogen peroxide using the Ti-TPyP reagent experimentally. This review deals with characterization of the high sensitivity and reaction specificity of the Ti-TPyP reagent for determination of hydrogen peroxide, to prove its reliability in analytical applications.

Determination of organic acids by high-performance liquid chromatography with electrochemical detection during wine brewing.

Voltammetric determination of acids by means of the electrochemical reduction of quinone was applied to high-performance liquid chromatography (HPLC) with electrochemical detection (ED) for determining organic acids in fruit wines. A two-channel HPLC-ED system was fabricated by use of an ion-exclusion column and an electrochemical detector with a glassy carbon working electrode. Aqueous solution of 0.1 mM HClO(4) and ethanol containing 2-methyl-1,4-naphthoquinone served as a mobile phase and reagent solution, respectively. Determination of acetic, citric, lactic, malic, succinic, and tartaric acids was made by measuring the peak areas of the flow signals due to the reduction current of quinone caused by the eluted acids. The peak area was found to be linearly related to the acid amount ranging from 0.1 to 40 nmol per 20 microL injection. The present method was characterized by reproducibility with the simple and rapid procedure without derivatization of analytes. The method was shown as an effective means for following acid contents in fruit juices during fermentation with wine yeast.