W. Franklin Smyth

Polarographic behaviour and analysis of some azo dyes of biological significance

The polarographic behaviour of the azo dyes CI Direct Orange 34, Acid Red 73, Direct Blue 84 and Direct Red 80 over the pH range 1–13 was studied. Mechanisms of reduction are postulated, the optimum pH ranges for the determination of the dyes by differential-pulse polarography are selected and the appropriate linear ranges deduced from calibration graphs.

Polarographic study of the acid-base equilibria existing in aqueous solutions of the 1,4-benzodiazepines

ZusammenfassungPolarographische (und auch spektralphotometrische) Untersuchungen haben gezeigt, daß 1,4-Benzodiazepine in wäßriger Lösung in wenigstens 3 Formen vorliegen, einer protonisierten, einer neutralen und einer anionischen. Die protonisierte Form läßt sich im allgemeinen polarographisch in einem weiten pH-Bereich reduzieren. Die sich ergebenden Stufen eignen sich zu analytischen Messungen im mg-Bereich (Pharmazeutica) oder im ng-Bereich nach selektiver Extraktion aus Körperflüssigkeiten.SummaryPolarographic and spectral investigations on aqueous solutions of the 1,4-benzodiazepines show the presence of at least three species, the protonated, neutral and anionic forms. The protonated form is generally polarographically reducible over a wide pH range and the resulting waves suitable for analytical measurements at the milligram level they occur in formulations or at the nanogram level after selective extraction from body fluids.

A study of the electrochemical oxidation of some 1,4-benzodiazepines

The electrochemical oxidation of the 1,4-benzodiazepines flurazepam, chlordiazepoxide, oxazepam, lorazepam, potassium chlorazepate, nitrazepam, flunitrazepam, prazepam, diazepam and medazepam and some of their metabolites has been investigated at a glassy carbon electrode in Britton-Robinson buffers (pH 2–10) and in 0.01 M sodium hydroxide solution, each containing 10% of methanol. Oxidation mechanisms are proposed and analytical applications for use in assays of formulations and biological fluids are recommended.

Polarographic method for the identification of 1,4-benzodiazepines

The polarographic behaviour of 12 therapeutically important 1,4-benzodiazepines in Britton-Robinson universal buffers, pH 4.0 and pH 12.0, has been investigated. Differences in the polarographic peak potentials of these compounds in these media are explained. The rates of hydrolysis of certain benzodiazepines in acidic solution were investigated. Bromazepam and flunitrazepam, both of which possess a strongly electron-withdrawing substituent on the 5-o-phenyl group, were found to undergo rapid acid hydrolysis. On the basis of these findings, and taking into account the extraction profile of some of the compounds over a pH range, a scheme is devised for the identification of any one or more of 12 1,4-benzodiazepines. It is suggested that this procedure would be applicable to the analysis of unknown formulations or body fluids in forensic cases where the parent compound exists in relatively high concentrations compared with its metabolites.

The polarographic behaviour of the 1,4-benzodiazepines, oxazepam and lorazepam, and a method for quality control☆

The polarographic behaviour of the drugs, oxazepam and lorazepam, has been investigated over a wide pH range. Different types of wave are obtained depending on the pH. The pKa, values calculated are in good agreement with those obtained from u.v. spectroscopic measurements. For analytical purposes, the optimal pH is 4.7 (acetate supporting electrolyte), the 4-electron reduction wave being measured. A quality control method for the two drugs in different formulations containing 0.5–15 mg of active constituent is described.

A spectral and polarographic study of the acid—base and complexing behaviour of bromazepam

Abstract A spectral and polarographic study of bromazepam yielded pKa values of 2.5, 5.2 and 11.8, corresponding to protonation at the azomethine and pyridine nitrogen atoms, and deprotonation at the nitrogen atom in position 1, respectively. These acid-base equilibrium reactions are discussed with reference to the hydrolysis and complexing properties of this compound. An indirect analytical method, based on the complexation of bromazepam with Cu2+ ions, has been investigated by differential pulse anodic stripping voltammetry.

Cathodic stripping voltammetry of 5-fluorouracil

An investigation has been carried out into the anodic differential-pulse polarographic and cathodic stripping voltammetric behaviour of the anticancer drug 5-fluorouracil at mercury indicator electrodes. The anodic peak, corresponding to the formation of a mercury salt, has been used for the determination of the drug in formulations with a relative standard deviation of 0.5%. The cathodic stripping voltammetric behaviour of this mercury salt can be used to monitor 10–7–10–8M concentrations of 5-fluorouracil in a borax-HClO4 buffer, pH 7.8. The interference of Cl– with the cathodic stripping signals is only evident at concentrations of Cl– four orders of magnitude higher than the concentration of the drug and uric acid was found not to interfere at up to equal concentrations of 5-fluorouracil. The cathodic stripping method has been applied to the determination of 5-fluorouracil in human serum.

A polarographic and spectral study of some c- and n- nitroso compounds

Abstract A wide range of N-nitroso compounds was investigated polarographically and spectrophotometrically. In general, the =N-N0 group is reduced in a 4-electron step in acidic media, which is most suitable for differential pulse polarographic analysis at the trace level. If the groups R and/or R attached to the nitrosamine group are saturated entities, then the resulting differential pulse polarographic peaks are broad and of little use in the resolution of mixtures. The limit of detection is of the order of 10 -6 M . If R and R are unsaturated, the polarographic peaks are much sharper, mixtures can be resolved and the limit of detection is of the order of 10 -7 M , C-Nitroso and C-nitro compounds are best determined by differential pulse polarography, because the waves are comparatively large and sharp, and because the reductions occur at relatively positive potentials where co-extractible interferences from foods, etc., will interfere to a minimal degree.

Applications of a voltammetric flow-through cell in on-line analysis for organic compounds

Abstract A flow-through voltammetric cell is described and the d.c. and pulse working modes are studied in on-line situations. On-line analysis of different compounds has been done by (a) direct oxidation at a glassy carbon electrode, (b) direct reduction or (c) direct oxidation at a mercury-coated solid electrode, and (d) cathodic stripping by first depos-iting the compound on a mercury film and then employing a cathodic d.c. voltage scan. The linear range and the detection limit of the on-line method are better than those in quiescent solutions

Voltammetric determination of 2-, 3- and 4-chloroaniline in mixtures

The oxidative-voltammetric behaviour of 2-, 3- and 4-chloroaniline has been investigated at the glassy carbon electrode over the pH range 1–12. The optimum pH values for the linear-sweep and differential-pulse voltammetric determination of these compounds were found to be 1.95 for 2- and 3-chloroaniline and 8.1 for 4-chloroaniline. Differentiation of the three compounds in a mixture was achieved by using a combination of high-performance liquid chromatography with voltammetric detection. This method could be used to determine concentrations of 2- and 4-chloroaniline down to 2 ng and 3-chloroaniline down to 1 ng for a 20-µl injection on to the chromatographic column.