Oxidation Of Pyrogallol Red Research Articles

Determination of Chromium(VI) with Screen‐Printed Ex‐Situ Bismuth Ffilm Electrodes by Adsorptive Stripping Voltammetry

AbstractThis work presents a fast and sensitive method, with an ex–situ bismuth film screen‐printed carbon electrode (ex–situ Bi–SPCE), for the determination of Cr(VI) through adsorptive stripping voltammetry (AdSV) using Pyrogallol Red (PGR) as complexing agent. The method is based on the oxidation of PGR by Cr(VI) and posterior complexation with Cr(III). To obtain a sensitive and selective method, the effects of various parameters such as pH, ligand concentration of PGR (CPGR), accumulation potential, and accumulation time (Eacc, tacc) were optimized. The optimal conditions using Bi–SPCE prepared ex–situ were pH 4.5 (0.01 mol L−1 acetic acid/acetate buffer), CPGR: 2.6 μmol L−1, Eacc: −0.70 V and tacc: 60 s. Peak current is proportional to Cr(VI) concentration over the range 0.23–12.0 μg L−1, with a 3σ detection limit of 0.97 μg L−1. The method was validated by determining Cr(VI) in tap water spiked with Cr(VI) and Cr(III).

Mechanistic studies on the effect of veratryl alcohol on the lignin peroxidase catalyzed oxidation of pyrogallol red in reversed micelles

Abstract The lignin peroxidase (LiP) catalyzed oxidation of pyrogallol red (PR) in the absence and presence of veratryl alcohol (3,4-dimethoxybenzyl alcohol, VA) was carried out in bis (2-ethylhexyl) sulfosuccinate sodium (AOT)/ polyoxyethylene lauryl ether (Brij30) reversed micelles to elucidate the role of VA. Results indicated that VA could accelerate the LiP catalyzed oxidation of PR, especially at low H2O2 concentrations. Unlike in bulk aqueous medium, the protection of LiP by VA in the present medium was relatively unsubstantial, even at high H2O2 concentrations. Analysis of data from a series of experiments showed that the enhancement of the PR oxidation caused by VA was mainly due to the indirect oxidation of PR by VA+∙ from the LiP catalyzed oxidation of VA. It was also found that at the same protector concentration (40 μM), VA (the physiological substrate of LiP) was less effective than PR (a phenolic compound) in protecting LiP from the H2O2 derived inactivation. This novel phenomenon deserves further study.

Reactions of Peroxynitrite and Nitrite with Organic Molecules and Hemoglobin

In this work, the reactions of nitrite (NO2-) and peroxynitrite (ONOO-) with organic molecules as well as with hemoglobin (Hb) were examined and the potential interference with the detection of hydrogen peroxide and Hb was investigated. ONOO- at low concentrations (35-140 microM) induced a concentration-dependent oxidation of o-phenylenediamine and guaiacol, and this process can be improved by the addition of Hb in a concentration-dependent manner. This enhancing effect of Hb was possibly due to the formation of such highly reactive species as ferrylHb during the reaction of ONOO- and Hb. NO2- also oxidized the aromatic amine o-phenylenediamine, but its efficiency was much lower than that of ONOO-. A 300-fold excess of NO2- over hydrogen peroxide inhibited the oxidation of Pyrogallol Red mediated by hydrogen peroxide and Hb, which was due in part to the reaction of NO2- with Hb ferryl species compound I and compound II and the phenoxyl radical. These data suggest that ONOO- and NO2- can interfere with the detection of hydrogen peroxide. The overestimation or underestimation of the hydrogen peroxide detected is dependent upon the organic molecule utilized for detection and the relative rate of NO2-, superoxide, and ONOO- generation.

The determination of total concentration and activity of antioxidants in foodstuffs

We developed a new method for the analysis of active antioxidants that is based on their reactions with the ABTS+. cation radical obtained by oxidation of ABTS, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt. The feasibility of this method was confirmed by electrochemical and kinetic studies of model antioxidants. ABTS+. was shown to react rapidly with active and slowly with weak antioxidants, which allows it to be used as a model radical for the quantitative determination of the total content of natural antioxidants (antioxidant equivalent) in natural extracts and wines. Another analytical method based on the competitive oxidation of Pyrogallol Red (a detecting molecule) and the examined antioxidants by radicals derived from peroxynitrite was used for measuring the relative activity of antioxidants. A combination of both methods helped measure the total concentration of antioxidants and their average specific activities (per molecule of active compound) in extracts from grape, olive, and tomato and concentrates of various popular beverages (wines, beers, and juices), as well as in the commercial concentrated food product Kréto-A, made from grape, red wine, tomato, and olive. Red wine and red grape juice were shown to be the most rich in antioxidants (up to 20 mM), with their activity being similar to that of polyphenols. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2002, vol. 28, no. 6; see also http://www.maik.ru.

Thermodynamic and Kinetic Studies on Oxidation of Pyrogallol Red by Hydrogen Peroxide in the Absence and Presence of Molybdenum(VI)

The oxidation of pyrogallol red (PGR) by hydrogen peroxide has been studied both in the absence and presence of molybdenum(VI) at pH of 7.0 by spectrophotometric detection. The reaction rate was studied with a fix-time method from 0.5 to 4.5 min. The effect of reagents concentration, ionic strength and temperature was studied to give the optimum conditions. At the optimizing conditions the rate constant, energy and entropy of activation and frequency factor have been calculated using the Arrhenius and Eyring plots.

Kinetics-Based Indirect Spectrophotometric Method for Simultaneous Determination of MnO4 (-) and Cr2O7 (2-): A Modern Instrumental Analysis Laboratory Experiment

An indirect kinetics-based spectrophotometric method is developed for the simultaneous quantitative determination of permanganate and dichromate ion concentrations in an unknown. The method is based upon differences in reaction times between pyrogallol red and the two analytes. Oxidation of pyrogallol red (PGR) by permanganate ion is rapid, whereas oxidation of PGR by the dichromate ion is much slower. From changes in the measured absorbances after 3-and 8-minute reaction times, the molar concentrations of the permanganate and dichromate ions are determined.

Kinetic-Spectrophotometric Determination of Thiocyanate Based on Its Inhibitory Effect on the Oxidation of Pyrogallol Red by Bromate

A kinetic spectrophotometric method for rapid measurement of thiocyanate in serum, urine and sewage water with no need for removed of interfering substances in described. The method is based on the inhibitory effect of thiocyanate on the oxidation of pyrogallol red by bromated and nitrite which is monitored at 467 nm. The variables affecting the rate of the reaction were investigated and the optimum conditions were established. Thiocyanate can be measured in the range of 0.010-0-0.500 mg/mL with a limit of detection of 0.001 mg/mL. The relative standard deviation for ten replicate determination of 0.025 mg/mL of thiocyanate is 1.5%.

Kinetic-Spectrophotometric Determination of Traces of Osmium by Its Catalytic Effect on the Oxidation of Pyrogallol Red by Hydrogen Peroxide

Abstract A Kinetic-spectrophotometric method for the determination of ultra-trace amounts of osmium(VIII) is described. It is based on the catalytic action of osmium(VIII) on the oxidation of pyrogallol red with hydrogen peroxide, yielding a colorless product in neutral medium. The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 540 nm and 30°C. Os(VIII) in the range 0.005 -100 ng.ml−1 can be determined. The proposed method is hardly subject to interferences. The relative standard deviation is 1.5% for 1 ng.ml−1 of Os(VIII). The kinetic parameters of the catalyzed and uncatalyzed reactions are reported. The detection limit is 1 pg.ml−1.

Improved method for the kinetic catalytic determination of lead(II) in dodecyltrimethylammonium micelles

The cationic surfactant dodecyltrimethylammonium bromide (DTAB) enhances the catalytic of lead(II) on the oxidation of Pyrogallol Red (PR) by peroxodisulphate. Lead(II) accelerates this reaction by forming a complex with PR which concentrates on the micellar surface. The micellar catalysis of DTAB was used for the kinetic spectrophotometric determination of lead(II) over the range 2–18 ng ml −1 (detection limit 1.3 ng ml −1), the relative precision for 10 ng ml −1 of lead(II) being 3%. The proposed method is highly selective and its analytical features are clearly superior to those of its counterpart involving an aqueous medium. The mechanism via which DTAB acts on the reaction was studied in depth.

Spectrophotometric determination of bromate by the oxidation of Pyrogallol Red

A method is proposed for the determination of bromate based on the oxidation of Pyrogallol Red (PGR) in a sulphuric acid medium. The kinetic data show that the initial reaction rate increases on increasing the sulphuric acid concentration. Under the optimum conditions of 2 mol dm–3 H2SO4 and a time of 5 min bromate can be determined in the range 0–3.08 × 10–5 mol dm–3; the limit of detection is 7 × 10–7 mol dm–3 of BrO3– and the limit of quantitation is 2.3 × 10–6 mol dm–3 of BrO3–. The stoicheiometry is 3:2 (bromate to PGR). The reaction is second order with respect to H2SO4 concentration, first order with respect to bromate concentration and 0.5 order with respect to PGR concentration. The precision, accuracy and selectivity of the method are discussed.

Spectrophotometric study of the cerium(IV)-pyrogallol red system

This study is based on the oxidation of Pyrogallol Red (PGR) by cerium(IV) under the following conditions: pH 5, temperature 25 °C and at a wavelength of 507 nm. The decrease in absorbance of a 6 × 10–5M PGR solution at a fixed time is proportional to the concentration of cerium(IV) over the range 0–15 p.p.m.; the limit of detection of cerium is 0.50 p.p.m.; the stoicheiometry of the system is 2:1 [cerium(IV): PGR]; and the reaction is first order with respect to cerium(IV). This paper describes studies on the selectivity of the method with respect to possible interference from 26 species, which have been classified according to their possible mechanism of interference. The system has a relative standard deviation in the range 3.1–0.3% for concentrations of cerium(IV) between 2 and 15 p.p.m. It does not present a constant-type error and does not require a blank correction at a fixed time of 5 min.

Kinetic-spectrophotometric determination of chromium(VI) by the oxidation of pyrogallol red

A spectrophotometric method is described for the determination of chromium(VI), which is based on the ability of chromium(VI) to oxidise Pyrogallol Red (PGR). For a fixed time the decrease in absorbance of the characteristic band of PGR (with λmax. at 490 nm and at pH 4) is proportional to the concentration of chromium(VI) in the range of 0–1.00 p.p.m. The limit of detection of chromium is found to be 0.05 p.p.m. using 6 × 10–5M PGR at pH of 4, an ionic strength of 0.1 M, a temperature of 25 °C and a wavelength of 490 nm.The oxidation of PGR by Cr(VI) is first order with respect to Cr(VI). This paper describes studies of the selectivity of the method with respect to possible interferences from 22 species, which have been classified according to their possible interference mechanism. The precision and accuracy of the method for times of between 5 and 20 min are also described.

Kinetic-spectrophotometric determination of manganese and vanadium + manganese by oxidation of pyrogallol red

Spectrophotometric methods for the determination of manganese and the simultaneous determination of vanadium + manganese, based on the oxidation of Pyrogallol Red (PGR), are described. Manganese or vanadium + manganese are determined by the decrease in the absorbance of the characteristic band at 490 nm at pH 4. At pH 4, an ionic strength of 0.1 M, a temperature of 25 °C and a wavelength of 490 nm, there is a linear relationship between the absorbance of PGR (6×10–5M), at a fixed time, and the concentration of manganese(VII) over the range 0–1.10 p.p.m. The limit of detection of manganese is 0.03 p.p.m. Studies were made of the selectivity of the method with respect to possible interferences from 22 species, which have been classified according to their possible mechanism of interference. The precision and accuracy of the method using a fixed time of 5 min were also determined. The simultaneous determination of vanadium in the range 0.20–1.83 p.p.m. and manganese(VII) in the range 0.11–1.10 p.p.m. by using a system of equations in which the absorbance at a fixed time is considered to be proportional to the total concentration of the two elements and their effects on the absorbance of PGR are additive, is described.

Determination of vanadium by means of its catalytic effect on the potassium bromate oxidation of Pyrogallol Red

The method is based on the oxidation of Pyrogallol Red (PGR) by potassium bromate. Vanadium is determined by means of its catalytic effect on this oxidation, under the following conditions: pH 4, ionic strength 0.1 M, temperature 25 °C and at a wavelength of 490 nm. The decrease in absorbance of PGR (6 × 10–5M) in the presence of KBrO3(4.4 × 10–3M), at a fixed time, is proportional to the concentration of vanadium(V) over the range 0–50.94 p.p.b. The limit of detection of vanadium is found to be 0.61 p.p.b. The precision and accuracy of the method, using a fixed time of 5 min, is described. The selectivity of the method with respect to the possible interference of 23 species is also described. Starting from the oxidation of PGR (6 × 10–5M), at pH 4, and by means of the V(V)-KBrO3-PGR and V(V)-PGR systems it is possible to carry out the determination of vanadium(V) between 0.61 p.p.b. and 1.83 p.p.m., measuring the absorbance values at times of 5 and 10 min, with and without KBrO3.

Spectrophotometric determination of vanadium by oxidation of pyrogallol red

A spectrophotometric method of vanadium determination is described. It is based on the oxidation of Pyrogallol Red (PGR) and vanadium is determined by the decrease in absorbance of its characteristic band at 490 nm and at pH 4. This absorbance decrease is proportional to the concentration of vanadium(V). At a pH of 4, an ionic strength of 0.1 M, a temperature of 25 °C and a wavelength of 490 nm, there is a linear relationship between the absorbance of PGR (6 × 10–5M), at a fixed time, and the concentration of vanadium(V) over the range 0–1.83 p.p.m. The limit of detection of vanadium is found to be 0.05 p.p.m. In the presence of potassium bromate, the determination is possible at the parts per billion level. This paper describes studies of the selectivity of the method with respect to possible interference from 20 important species contained in ferrous and non-ferrous alloys, which have been classified according to their possible mechanism of interference. The precision and accuracy of the method at times of 5 and 10 min are also described.