Research Center for Materials Science

The kinetics of oxidation of iota-and lambda-carrageenan as sulfated carbohydrates by permanganate ion in aqueous perchlorate solutions at a constant ionic strength of 2.0 mol dm À3 have been investigated spectrophotometrically. The pseudo-first-order plots were found to be of inverted S-shape throughout the entire courses of reactions. The initial rates were found to be relatively slow in the early stages, followed by an increase in the oxidation rates over longer time periods. The experimental observations showed first-order dependences in permanganate and fractional first-order kinetics with respect to both carrageenans concentration for both the induction and autoacceleration periods. The results obtained at various hydrogen ion concentrations showed that the oxidation processes in these redox systems are acid-catalyzed throughout the two stages of oxidation reactions. The added salts lead to the prediction that Mn III is the reactive species throughout the autoacceleration periods. Kinetic evidence for the formation of 1:1 intermediate complexes was revealed. The kinetic parameters have been evaluated and tentative reaction mechanisms in good agreement with the kinetic results are discussed.

The kinetics of oxidation of carboxymethyl cellulose (CMC) by permanganate ion in aqueous perchloric acid at a constant ionic strength of 2.0 mol dm À3 has been investigated, spectrophotometrically. The reaction time curves of the pseudo first-order plots were of inverted S-shape throughout the entire course of reaction. The initial rates were found to be relatively slow in the early stages, followed by an increase in the oxidation rates over longer time periods. The experimental results indicated first-order kinetics in permanganate and fractional second-order dependence with respect to CMC concentration in either the induction or autoacceleration periods. Kinetic evidences for the formation of 1:2 intermediate complexes were revealed in both stages. The influence of the [H + ] on the reaction rates showed that the oxidation reactions are acid-catalyzed in both stages. Added salts indicated that Mn III and/or Mn IV play an important role in the reaction kinetics. The kinetic parameters have been evaluated and a reaction mechanism consistent with the experimental kinetics is suggested.

The kinetics of oxidation of carboxymethyl cellulose (CMC) by permanganate ion in aqueous perchloric acid at a constant ionic strength of 2.0 mol dm À3 has been investigated, spectrophotometrically. The reaction time curves of the pseudo first-order plots were of inverted S-shape throughout the entire course of reaction. The initial rates were found to be relatively slow in the early stages, followed by an increase in the oxidation rates over longer time periods. The experimental results indicated first-order kinetics in permanganate and fractional second-order dependence with respect to CMC concentration in either the induction or autoacceleration periods. Kinetic evidences for the formation of 1:2 intermediate complexes were revealed in both stages. The influence of the [H + ] on the reaction rates showed that the oxidation reactions are acid-catalyzed in both stages. Added salts indicated that Mn III and/or Mn IV play an important role in the reaction kinetics. The kinetic parameters have been evaluated and a reaction mechanism consistent with the experimental kinetics is suggested.

An investigation of the oxidation behaviour of the anti-inflammatory drug Piroxicam and a new one which is similar in structure and activity (Tenoxicam) at the carbon paste electrode (CPE) is presented. These compounds show a relatively similar voltammetric behaviour and degree of accumulation at the CPE surface. However, modification of the CPE with laurie acid improves sensitivity and also its selectivity, especially in complex media such as ur:me etc. To eliminate potent interfering compounds such as uric acid and ascorbic acid, the medium exchange rae:hod was also applied. A somewhat ~tronger adsorption of Tenoxicarn than of Piroxicam was observed and therefore a lower concentration fimit of finearity is obtained for Tenoxicam. After 60 s preconcentration, a detection limit of nearly 1 × 10-9 M for both Piroxicam and Tenoxicarn could be determined. This method seems to be suitable for determinations in biological fluids.