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The present paper describes a novel and fairly inexpensive catalytic kinetic method for the determination of Pd 2 + in the concentration range 17.71–177.14 ppb (ng mL − 1 ). The method is based on the catalytic effect of Pd 2 + on the substitution of cyanide by 4-cyanopyridine (4-CNpy) in hexacyanoferrate(II) in acidic media. The reaction was followed by measuring an increase in the initial rate of the indicator reaction with respect to the product, [Fe(CN) 5 (4-CNpy)] 3 − , formation at 477 nm. The effects of various parameters, such as pH and ionic strength of the reaction medium, concentration of the reactants and temperature, on the rate of the indicator reaction were studied to optimize the reaction conditions to achieve the highest sensitivity and to get lowest limit of detection of [Pd 2 + ]. The fixed time procedure, as a measure of the initial rate, was followed to obtain a linear regression equation relating the absorbance and [Pd 2 + ] in the range 17.71–177.14 ppb i.e. 1 × 10 − 7 to 1 × 10 − 6 mol L − 1 . The effects of the presence of various cations commonly associated with Pd 2 + and some anions have also been investigated and discussed. The detection limit of the method was calculated to be 9 ppb. The maximum average error of the proposed method was quite low. The method was successfully applied for the determination of Pd 2 + in synthetic and environmental water samples. The proposed method is selective, accurate and inexpensive compared to many other methods available in literature for Pd 2 + determination. [ABSTRACT FROM AUTHOR]

The kinetics and mechanism of formation of [Fe(CN)5INH]3- by a ligand substitution reaction between aquapentacyanoferrate(II) ion and isoniazid, (pyridine-4-carboxylic acid hydrazide) (INH) have been investigated spectrophotometrically in acidic media at 435 nm ( lmax of product), under pseudo-first order conditions, using excess of INH over [Fe(CN)5H2O]3-. The reaction was studied as a function of [Fe(CN)5 H2O3-], [INH], pH, ionic strength and temperature, by varying only one of these variables while other variables were held constant. The reaction exhibited first-order kinetics in [INH] while it was independent of [Fe(CN)5H2O3-] in the chosen concentration range. The effect of temperature on the reaction rate yielded the activation parameters. The most plausible mechanism consistent with the experimental results has been proposed. [ABSTRACT FROM AUTHOR]

Abstract: The interaction of isoniazid (INH) with [Fe(CN)5(H2O)]3− in aqueous solution at pH3.8 was found to give intensely golden yellow color product, [Fe(CN)5(INH)]3−, which strongly absorbs at 435nm without any interference with the reactants. The effect of several reaction variables on the rate of the complex [Fe(CN)5(INH)]3− formation was studied and optimized. Thus a simple, rapid, selective and economical analytical method based on the ligand substitution (LS) kinetic assay of INH in pure as well as in dosage forms involving the reaction between [Fe(CN)5(H2O)]3− and INH has been reported. The isoniazid can be determined in the range 1.37–13.71μgmL−1 by measuring the initial rate of the complex formed during the course of the reaction at 435nm. The detection limit has been established to be 0.15μgmL−1 of INH. Recovery experiment was carried out to ensure the accuracy and the precision in the quantification of INH. The proposed method has successfully been applied for the analysis of INH in pure samples and a number of its pharmaceutical formulations with excellent accuracy and precision while the results were compared with those obtained by the official analytical method, and were in well agreement. The common excipients used as additives in pharmaceuticals do not interfere in the proposed method. It was possible to do 20 analyses per hour. [Copyright &y& Elsevier]