Einar Jacobsen

Effects of surfactants in differential pulse polarography

Abstract Differential pulse polarograms of surfactants exhibit tensammetric peaks at the adsorption and desorption potentials of the surfactant. In the potential range where adsorption occurs the base current is depressed. The heights of the tensammetric peaks are nonlinear functions of the bulk concentration of the surfactant. Differential pulse polarograms of reducible substances are greatly affected by the presence of surfactants, the effect being similar to that observed in a.c. polarography. Surfactants with the same charge as the depolarizer act as electrochemical masking agents, whereas peak currents may be enhanced by oppositely charged surfactants.

Polarographic determination of folic acid in pharmaceutical preparations.

Abstract A.c. polarograms of folie acid recorded from acetate buffer pH 5.5 exhibit a very welldefined wave at the dropping mercury electrode. The current is diffusion-controlled and proportional to the concentration; the optimal range of measurement is 0-24 μg ml -1 . Two electrons and two hydrogen ions are involved in the reduction. With the phase-sensitive a.c. polarographic method, the calibration graph is linear in the 2 × 10 -8 —2 × 10 -6 M range. The method proposed for the determination of folic acid in tablets is very simple and rapid, and does not involve time-consuming separation of iron salts and insoluble constituents in the tablets.

Electrochemical reduction of chlordiazepoxide at mercury electrodes

The electroreduction of chlordiazepoxide has been investigated by polarography, cyclic voltammetry and coulometry at controlled potential. In 0.1 M sulphuric acid the drug is reduced in two steps. The first step is a 2-electron reduction of the N-oxide group and the second step a 2-electron reduction of the C=N group. Two hydrogen ions are consumed in each step. The current is diffusion-controlled and proportional to the concentration in the range 2.5 10−6–10−3M. The drug is strongly adsorbed at the electrode, so that it can be determined in biological materials without prior separation. A rapid polarographic method for the determination of chlordiazepoxide in tablets is described.

Electroreduction and polarographic determination of nitrazepam in serum

Abstract The electroreduction of nitrazepam has been investigated by polarography, cyclic voltammetry, chronopotentiometry and controlled potential coulometry. The drug is decomposed in acidic and alkaline solutions but is fairly stable in neutral media. In phosphate buffer pH 6.9 the reduction occurs in two steps. The first step is a 4-electron reduction of the nitro group to the hydroxylamine and the second step is a 2-elcctron reduction of the azomethine (>C=N-) group. The first polarographic wave probably involves a rate-determining 2-electron reduction of the nitro group. This wave is well defined and suitable for determination of the drug in the range 10 −6 - 5·10 −4 M . The half-wave potential is -0.38 V vs . Ag/AgCl, and the current is diffusion-controlled. The oxidized form of nitrazepam is strongly adsorbed at the electrode surface, hence the drug can be determined in the presence of surface-active substances like proteins. A procedure has been developed for the direct polarographic determination of microgram quantities of the drug in serum. The proposed method is very rapid and accurate and permits determination of 0.5 -80 μg per ml of the drug in serum.

Effects of surface-active substances on polarographic waves of some complexes

Abstract The effect of the charge type of surface-active substances on the polarographic waves of various complexes has been investigated. The results indicate that the polarograms are practically unaffected by the presence of a aurfactant, provided that the adsorbed layer has a charge opposite to that of the depolariser. Polarographic waves of depolarisers with the same charge as the adsorbed layer are, however, shifted to more negative values or greatly distorted. The distorting effect is qualitatively interpreted in terms of an electrostatic repulsion between the adsorbed layer and the depolariser. The charge type of a surfactant seems to be important for the appropriate choice of a nondistorting maximum suppressor.

Effects of ionic surfactants on polarographic waves

Summary The effect of various ionic surfactants on polarographic waves has been studied using bismuth-DCTA and copper-tetren as depolarizers. The presence of surfactants with the same charge as that of the depolarizer, and high molecular weight surfactants with complicated molecular structure, decreases the rate of the electron-transfer reaction, and the polarographic waves are greatly distorted. However, the presence of aliphatic surfactants with an unbranched chain and a charge opposite to that of the depolarizer do not cause any distortion on either d.c. or a.c. polarographic waves. Moreover, in some cases the presence of such surfactants make the electrode reaction more reversible. The possible application of ionic surfactants in a.c. polarographic analysis is discussed.

Polarographic determination of chloramphenicol

Abstract The electroreduction of chloramphenicol has been studied by polarography, cyclic voltammetry, chronopotentiometry and coulometry. The experimental results lead to the conclusion that the drug undergoes a slow 2-electron reduction of the nitro group which is followed by a fast 2-electron reduction to hydroxylamine. At more negative potentials the hydroxylamine group is further reduced to the amine. In acetate buffer pH 4.7 with 0.003 % decylamine present, the drug produces a very well-defined, diffusion-controlled 4-electron polarographic wave. The current is proportional to the concentration and permits the drug to be determined by polarography in the concentration range 0.3–600 μg ml -1 . A rapid polarographic method for the determination of chloramphenicol in milk is proposed.

Determination of 1-thyroxdine sodium and 1-triiodo- thyronine sodium in tablets by differential pulse polarography

Abstract Differential pulse polarograms of thyroxine and of triiodothyronine recorded from 0.1 M sodium carbonate exhibit a well-defined peak at —1.060 and —1.050 V vs.Ag/AgCl, respectively, and the peak current is proportional to the concentration in the range 10 -6 —5 × 10 -5 M. A simple and rapid method is proposed for the determination of the drugs in tablets. The procedure does not involve time-consuming extractions or decomposition of organic matter, and it is suitable for control of content uniformity in pharmaceutical formulations.

Polarographic determination of thallium

Abstract A polarographic method for the determination of thallium is described. The inclusion of DTPA and Triton X-100 in the supporting electrolyte shifts the waves of interfering metals to considerably more negative potentials while the thallium wave is completely unaffected. An acetate buffer of pH 4–5 is the preferred base electrolyte, because a Tl-DTPA complex is formed at higher pH values. The polarographic behaviour of the complex is described and the stability constant determined.

Differential pulse polarographic determination of hydrocortisone in pharmaceutical preparations

Abstract Differential pulse polarograms of hydrocortisone recorded from acetate buffer pH 4.6 exhibit a well-defined peak at —1.25 V vs. SCE and the peak current is proportional to the concentration in the range 10 -5 –8 × 10 -5 M. The electrode reaction involves one electron and one hydrogen ion. A simple rapid method is proposed for the determination of hydrocortisone in creams and ointments. The procedure does not involve time-consuming extractions, but it is not applicable to samples containing surfactants like polyethyleneglycol which are more strongly adsorbed on the electrode than hydrocortisone. Because degradation in the side chain of hydrocortisone is not detected polarographically, the method is suitable for production control but not for stability tests.