T. Pérez Ruiz

Flow-injection fluorimetric determination of penicillamine and tiopronin in pharmaceutical preparations

Two flow-injection methods for the fluorimetric determination of penicillamine and tiopronin are proposed. The procedures are based on the oxidation of these drugs by thallium(III). In hydrochloric acid medium the fluorescence of thallium(I) formed in the oxidation of penicillamine or tiopronin is monitored using excitation and emission wavelengths of lambda ex = 227 nm and lambda em = 419 nm respectively. Linear calibration graphs were obtained between 3 x 10(-7) and 8 x 10(-6) M for penicillamine and between 8 x 10(-7) and 2 x 10(-5) M for tiopronin with sampling frequencies of 90 and 45 samples h-1 respectively. The relative standard deviations were in the ranges 0.48-0.29% for penicillamine and 1.04-0.31% for tiopronin. The applicability of the method to the determination of both drugs in pharmaceutical preparations was demonstrated by investigating the effect of potential interferences and by analysis of commercial preparations.

Coated-wire ion-selective electrode for the determination of gold(III)

Abstract A coated-wire gold(III)-selective electrode based on the 1,2,4,6-tetraphenyl-pyridinium tetrachloroaurate(III) ion-pair is described. The response is Nernstian in the gold concentration range 10−2–3 × 10−6 (slope 59.0 mV/pAu). Of the 22 ions tested, only the interference of thallium(III) is important. The electrode is applied to the determination of gold in an Ag-Pd-Au alloy with satisfactory results.

Simultaneous Flow Injection Determination of Diquat and Paraquat in Foodstuffs, Natural Waters and Biological Fluids

Abstract The reduction of diquat and paraquat with alkaline sodium dithionite has been applied to the simultaneous determination of both herbicides using a flow injection system. A dual-channel manifold with two detectors in parallel was used. The sample bolus is split into two subplug, one of the sub-boluses merges with a 0.1% sodium dithionite stream and routes to a spectrofluorimeter where diquat is determined. The other sub-bolus merges with a 0.5% sodium dithionite stream and routes to a spectrophotometer for the measurement of paraquat. The system allows 70 samples to be analysed per hour. Applications of the method to the determination of diquat and paraquat in real samples are reported.

Spectrophotometric determination of gold with 2-(p-methoxyphenyl)-5,7-diphenyl-1,3,4-thiadiazolo-(3,2-a)-pyridinium chloride

SummaryIn 0.4M hydrochloric acid medium, gold(III) forms with 2-(p-methoxyphenyl)-5,7-diphenyl-1,3,4-thiadiazolo(3,2-a)pyridinium chloride (TDZP) an ion-association compound which is extractable into isoamyl acetate. The extracted ion-pair, which has an Au:TDZP mole ratio of 1∶1, is used for the spectrophotometric determination of gold (ε=3.80 x 104l·mole−1·cm−1) in the concentration range 1–25μg of gold per 5 ml of organic solvent. The interference of a number of foreign ions has been investigated. The method is applicable to the determination of gold in ores.ZusammenfassungIn 0,4 M Salzsäure bildet Gold(III) mit TDZP eine Ionenassoziationsverbindung, die sich mit Isoamylacetat extrahieren läßt. Diese im Molverhältnis Au:TDZP=1∶1 zusammengesetzte Verbindung dient zur spektrophotometrischen Goldbestimmung (ε=3,80 x 104l·Mol−1·cm−1) im Konzentrationsbeieich 1–25μg Au/5 ml organisches Lösungsmittel. Die störende Wirkung von Fremdionen wurde untersucht. Das Verfahren eignet sich zur Goldbestimmung in Erzen.

Indirect photokinetic microdetermination of fluoride

Abstract A catalytic-kinetic method for the determination of nanogram amounts of fluoride based on its inhibiting action on the catalyst in the iron(III)-catalyzed photooxidation of thionine is described. The rate measurements are accomplished very simply by measuring the decreasing of absorbance after illumination for a fixed time.

N-substituted 4,6-diphenylpyridine-2-thiones: new photometric reagents for mercury

SummaryThe synthesis and applications of the 1-(p-chlorobenzyl), 1-(p-methylbenzyl), 1-(p-methoxybenzyl) and 1-(2-furylmethyl)N-substituted pyridine-2-thiones are described. These reagents form 2∶1 complexes with mercury(II), with λmax 314 nm. These complexes are useful for the spectrophotometric determination of mercury(II) in the concentration range 0.2–2.0μg/ml in the measurement solution. The apparent stability constants of the complexes have been calculated and the interferences of many foreign ions investigated. The method is applicable to the determination of mercury in Pharmaceuticals.ZusammenfassungDie Synthese und die Anwendung der 1-(p-chlorbenzyl)-, 1-(p-methylbenzyl)-, 1-(p-methoxybenzyl)- und 1-(2-furylmethyl)-substituierten Pyridin-2-thione wurden beschrieben. Diese Reagenzien bilden 2∶1-Komplexe mit Hg(II), deren maximale Absorption bei 314 nm liegt. Diese Komplexe eignen sich für die spektrophotometrische Bestimmung von Hg(II) im Konzentrationsbereich 0,2–2,0μg/ml in der zu messenden Lösung. Die scheinbaren Stabilitätskonstanten dieser Komplexe wurden berechnet und die störende Wirkung vieler Fremdionen untersucht. Das Verfahren eignet sich für die Hg-Bestimmung in pharmazeutischen Präparaten.

Coulometric determination of organic compounds with methylviologen cation-radical

Abstract The scope of coulometrically generated viologen radical-cation as a reagent for the determination of organic compounds such as o-nitrophenol, p-nitrophenol, p-benzoquinone, and dichloroindophenol was investigated. Samples of the order 10−5 to 10−4 μmol could be determined with about 1% precision and accuracy. These organic compounds react quantitatively and rapidly with the viologen radical-cation, which can be electrolytically generated with 100% current efficiency. A sensitive biamperometric end point detection can be applied.

Titration of oxidants with the reduced species of phenosafranine and neutral red, generated by electrochemical and photochemical techniques

SummaryThe generation of the reduced species of phenosafranine and Neutral Red by coulometric and photolytic methods is described. The electrogeneration is done at a platinum or mercury cathode, and the photogeneration by photochemical reaction between EDTA and the dye. The redox potentials for phenosafranine and Neutral Red are very low. The reduced dyes are suitable as reductimetric titrants and have been applied in coulometric and photochemical titrations of periodate, chromium(VI), iron(III), cobalt(III) and 2,6-dichloroindophenol.ZusammenfassungDie Herstellung der reduzierten Formen von Phenosafranin und Neutralrot mit coulometrischen bzw. photolytischen Methoden wurde beschrieben. Ersteres erfolgt an einer Platin- oder Quecksilberkathode, letzteres durch photochemische Reaktion zwischen EDTA und dem Farbstoff. Die Redox-potentiale für Phenosafranin und für Neutralrot sind sehr niedrig. Die reduzierten Farbstoffe eignen sich als reduktometrische Titranten und wurden für coulometrische und photochemische Titrationen von Perjodat, Chrom(VI), Eisen(III), Kobalt(III) und 2,6-Dichlorindophenol verwendet.