A. Guiraúm Pérez

Kinetic-spectrophotometric determination of traces of vanadium(V) by its catalytic effect on the oxidation of 1,4-dihydroxyphthalimide dioxime with bromate

Abstract A kinetic-spectrophotometric method for the determination of trace amounts of vanadium(V) is described. It is based on the catalytic action of this ion on the oxidation of 1,4-dihydroxyphthalimide dioxime by bromate, which yields a red-violet product in acidic medium. The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 500 nm and 30°C. Using several kinetic methods (tangent, fixed-time and fixed-absorbance), vanadium(V) in the range 10–400 ng ml−1 can be determined. The proposed methods are hardly subject to interferences. The tangent method was used for the determination of vanadium in atmospheric particulate matter, human serum and synthetic mixtures. The kinetic parameters of the catalysed and uncatalysed reactions are reported.

Spectrophotometric study of a ternary zirconium/fluoride/alizarin complex with application to the determination of zirconium

A ternary zirconium/fluoride/alizarin complex is extracted into methyl isobutyl ketone. The apparent molar absorptivity at 556 nm is 1.52 × 105 1 mol−1 cm−1. The r.s.d. is 1.3% for 10 μg Zr (n = 12). There are several interferences, some of which can be masked with EDTA.

Electrochemical oxidation of cisatracurium on carbon paste electrode and its analytical applications.

The electrochemical oxidation of cisatracurium was investigated by cyclic voltammetry and differential pulse voltammetry at a carbon paste electrode and the experimental parameters have been optimized in order to obtain the optimum analytical signal. A differential pulse voltammetric method with carbon paste electrode is described for the determination of cisatracurium with detection limit of 0.38 mug/ml and quantitation limit of 1.26 mug/ml. The proposed method was applied to determine the content of cisatracurium in human urine and human serum, obtaining accurate and precise results.

Extraction and spectrophotometric determination of titanium(IV) with alizarin and fluoride

The characteristics of the mixed-ligand titanium(IV)-fluoride-alizarin complex, including the optimum conditions of formation and extraction into methyl isobutyl ketone, are described. A simple and sensitive procedure for spectrophotometric determination of titanium has been developed. At pH 9.5-10.3 titanium reacts with alizarin in the presence of fluoride to form a red-violet complex that is completely extractable into methyl isobutyl ketone, and has its absorption maximum at 513 nm. The molar absorptivity at 513 nm is 7.0 x 10(4)l.mole(-1).cm(-1). Beers law is obeyed up to 22 mug of titanium in 30 ml of solution. The method has been used for the determination of titanium in an oxide mixture and aluminium alloy samples.

Electrochemical behaviour and determination of acrivastine in pharmaceuticals and human urine

Abstract The differential pulse polarography, DC-tast polarography and cyclic voltammetry behaviour of acrivastine was studied in Britton–Robinson buffer solutions (pH 2–11.7). In acidic media, a non-reversible diffusion controlled reduction process involving four electrons takes place. Two reduction waves appear at a E1/2=−0.6 and −0.99 V. The reduction mechanism is discussed. The linear relationship between peak current height and acrivastine concentration allowed the differential pulse polarographic determination of acrivastine over a wide concentration range, from 0.35 to 26.1 mg l−1at pH 2.5. The procedure was applied to determination of the drug in pharmaceutical formulations and human urine samples.

Differential-pulse polarographic determination of iron in acids, waters, fruit juices and wines

A method for the determination of iron by differential-pulse polarography, based on the formation of a 5,5-dimethylcyclohexane-1,2,3-trione 1,2-dioxime 3-thiosemicarbazone–iron(II) complex, is proposed. The method was applied to the determination of iron in acids, waters, wines and fruit juices.

Salicylaldehyde-1-phthalazinohydrazone as an analytical reagent.

The synthesis, characteristics and analytical properties of salicylaldehyde-1-phthalazinohydrazone are described. Spectral characteristics, pK values, the effect of oxidizing and reducing agents, resistance to hydrolysis, and reactions with common cations are reported.

Solvent effects on the dissociation of bromopyridinium ions in N,N-dimethylformamide mixtures by electrochemical measurements

Abstract Thermodynamic proton dissociation constants of 2-, 3- and 4-bromopyridinium ions were evaluated by using potentiometric and polarographic techniques in 20–60% (v/v) N,N-dimethylformamide/water mixtures at 25 ± 0.1°C, applying an empirical pH correction for mixed aqueous solvents. Non-electrostatic factors exert a considerable influence on the dissociation of halopyridinium ions. The solvation numbers for these ions were determined by analysing the experimental data mathematically.

Electrochemical reduction at a mercury electrode and differential-pulse polarographic determination of dibucaine in pharmaceutical ointments

The polarographic behaviour of dibucaine was studied using various electrochemical techniques. In acidic media, a non-reversible diffusion-controlled reduction process involving two electrons takes place. The linear relationship between peak current intensity and dibucaine concentration allowed the differential-pulse polarographic determination of dibucaine over a wide concentration range, from 10–6 to 10–4 mol l–1 at pH 2.6, with a relative standard deviation of 1.9%(nine determinations at the 10–5 mol l–1 level). A simple extraction procedure was employed for the determination of the drug in pharmaceutical formulations and the validity of the method was confirmed by parallel determinations using the official method of the US Pharmacopeia (HPLC).

Polarographic determination of picolinaldehyde in the presence of some related compounds

Abstract A d.c. polarographic method is described for the determination of picolinaldehyde (1.5 × 10 −5 –2.9 × 10 −4 M), based on the in situ formation of its Girard-P derivative in aqueous solution. A mechanism of reduction ( E 1/2 = −0.71 V at pH 3.5) is proposed. The applicability of this method is checked in synthetic samples containing pyridine, picoline and pyridine carboxylic acids.