M. A. Ghandour

Determination of verapamil by adsorptive stripping voltammetry in urine and pharmaceutical formulations

A sensitive reduction peak of verapamil is obtained by adsorptive stripping voltammetry in 0.01 M phosphate (pH 7.4) at an accumulation time of 30 s. The peak potential is -1.81 V (vs. Ag/AgCl). The peak current is directly proportional to the concentration of verapamil (1x10(-8)-1x10(-6) M), with a 3sigma detection limit of 5x10(-10) M (0.246 ng/ml). The R.S.D. at the 1x10(-7) M level is 1.8%. The interference of some metal ions, and some amino acids, and the application of the method to analysis of urine, and pharmaceutical formulations are described. The method is simple (no extraction), rapid (30 s accumulation time), sensitive (the detection limit of verapamil is 0.491 ng/ml), reproducible(within day R.S.D. of 1.28-1.8%), and suitable for routine analysis of verapamil, urine, and pharmaceutical formulation.

CATHODIC STRIPPING VOLTAMMETRY OF THE ANTIHYPERTENSIVE DRUG CAPTOPRIL IN BOTH AQUEOUS AND BIOLOGICAL MEDIA

ABSTRACT Adsorptive stripping voltammetry is used for determination of trace levels of captopril in phosphoric acid (pH 2.3). The adsorptive peak was observed at −0.49 V vs. Ag/AgCl. The peak response was characterized with respect to pH, preconcentration time, possible interferences, deposition potential, supporting electrolytes and other variables. The obtained results were analyzed and the statistical parameters were calculated. Also the method was applied to determine the mentioned drug in pharmaceutical formulations, urine and blood-serum. The limit of detection was 0.019 ng/ml.

The electroreduction (polarographically) of uranyl ion in nitric acid and nitric acid-methanol mixture media

Abstract The polarographic reduction of uranyl ion in nitric acid solution are found to be one electron reduction mechanism at lower acid concentration (0.1 M HNO 3 ) and two electron mechanism at high acid concentration (2M HNO 3 ). Methanol shifted the half wave potentials to more negative values and increased the free energy. The free energies of reduction of U(VI) to U(V) in these mixed solvents are inversely proportional to both the dielectric constants and Gutmans Acceptor number of methanol. The U(V) is stable at pH 3, but its dismutation increased at lower and higher pHs than pH 3.

Adsorptive stripping voltammetric determination of antihypertensive agent: diltiazem ☆

Adsorptive stripping voltammetry was used to determine the antihypertensive agent diltiazem in phosphate buffer (pH 7.0). The adsorptive cathodic peak was observed at -1.72 V vs. Ag/AgCl. The peak response was characterized with respect to pH, preconcentration time, possible interferences, accumulation potential and supporting electrolytes. The obtained results were analyzed and the statistical parameters were calculated. The proposed method was applied to determine the mentioned drug in pharmaceutical formulation (capsule) and urine. The detection limit is 1x10(-8) M (4.5 ng ml(-1)) using 180 s preconcentration time, whereas the lower limit of detection is 6x10(-9) M (2.7 ng ml(-1)).

Polarographic Studies of Some Metal(II) Complexes with Cephalosporins Selected from the First Generation

Abstract Both differential pulse polarography and cyclic voltammetry techniques have been applied to investigate the coordination of Cd2+, Zn2+, and Pb2+ ions with some cephalosporins [cephalexin, cefadroxil, and cephaloridine] in unbuffered aqueous medium. Cephalexin exhibits four consecutive complexes with each of Cd2+ and Zn2+ ions are evidenced with increasing ligand concentration, their stoichiometrics 1:1, 1:2, 1:3, and 1:4 metal-to-ligand, respectively, while it forms three complexes only with Pb2+. Also, cefadroxil exhibits four complexes with Cd2+ ions and two only with Pb2+. It appears that, cefadroxil has no complexing properties towards Zn2+ ions. Cephaloridine however, gives four consecutive complexes with Zn2+ only and no complexation occurs with Cd2+ or Pb2+ ions. The reversibility of the electrochemical reaction has been confirmed using cyclic voltammetry. It appears that, the kind of the side chain fixed at the 7-position on the β-lactam ring and the basicity of ligands have influenced on the complexation reaction as illustrated by the different behaviour of the investigated ligands. The stability constants of the intermediates of the formed complexes were calculated.

Adsorptive stripping voltammetric determination of uranium with cephradine

Uranium adsorbed with cephradine is reduced on a hanging mercury drop electrode. This property was exploited in developing a highly sensitive stripping voltammetric procedure for the determination of uranium. A detection limit 2 × 10–9 mol l–1(0.5 µg l–1) of uranium ion is obtained with an 180 s accumulation time. Cyclic voltammetry was used to characterize the interfacial and redox behaviour. The effects of various parameters are discussed. Experimental conditions include the use of 5 × 10–6 mol l–1 cephradine in 0.05 mol l–1 sodium perchlorate (pH ≈ 6.5), an accumulation potential of 0.0 V versus SCE and a direct current stripping technique. The response is linear up to 5 × 10–6 mol l–1 uranium and the relative standard deviation at 1 × 10–7 mol l–1 UO2+ is 4.4%. The effect of other metal ions was investigated.

VOLTAMMETRIC STUDIES ON COMPOSITION AND STABILITIES OF COMPLEXES OF TETRACYCLINE AND OXYTETRACYCLINE WITH SOME METAL IONS IN AQUEOUS MEDIUM

SummaryThe composition and stability of complexes of tetracycline and oxytetracycline with Cu(II), Cd(II), Pb(II) and UO2(II) have been studied polarographically (direct current and differential pulse polarographic techniques) at 25±0.1°C. Differential pulse polarographic studies have been particularly helpful in deciding the nature of metal-drug interactions at low concentrations. The reduction of Cu(II)-tetracycline has been found to be irreversible and diffusion controlled with the presence of an adsorption component. In the system uranyl(II)-tetracycline the complex formed has a stoichiometry of 1:1 and logKox=4.04 which is very close to that obtained by potentiometric measurements. The peak half widthW1/2 of the Pb(II)-OTC system is 60 – 70mV indicating that the process is reversible and two electrons are consumed. The log β′ is 10.30 in 0.1 mol dm−3 NaClO4. In the Cu(II)-OTC system two complexes were formed with log β1′=8.50 and log β2′=14.10. Cyclic voltammograms were recorded using a hanging dropping mercury electrode for the systems Cu(II), Cd(II), Pb(II) and UO2(II)-OTC to examine the irregularities in both peak potentials and peak currents during the polarographic investigations.ZusammenfassungEs wurden Zusammensetzung und Stabilität von Tetracyclin- und Oxytetracyclin-Komplexen mit Cu(II), Cd(II), Pb(II) und UO2(II) polarographisch mittels Direktstrom- und differentieller Pulspolarographie-Technik bei 25±0.1°C bestimmt. Zur Aufklärung der Metall-Substrat-Wechselwirkungen bei geringen Konzentrationen waren insbesonders differentielle Pulspolarographie-Untersuchungen erfolgreich. Es wurde festgestellt, daß die Reduktion von Cu(II)-Tetracyclin irreversibel und diffusionskontrolliert verläuft. Im System Uranyl(II)-Tetracyclin hat der Komplex eine Stöchiometrie von 1:1 und ein logKoxvon 4.04; dieser Wert ist dem aus potentiometrischen Messungen erhaltenen sehr ähnlich. Die Peak-Halbwertsbreite des Pb(II)-OTC-Systems ist 60 – 70 mV und zeigt damit einen reversiblen Prozess bei Verbrauch von zwei Elektronen an. In 0.1 mol dm−3 NaClO4 ist log β′ 10.30. Im Cu(II)-OTC-System werden zwei Komplexe mit log β1′=8.50 und log β2′=14.10 gebildet. Die cyclischen Voltammogramme wurden unter Verwendung einer hängenden tropfenden Quecksilberelektrode für die Systeme Cu(II), Cd(II), Pb(II) und UO2(II)-OTC aufgenommen, um die Unregelmäßigkeiten der Peak-Potentiale und der Peak-Ströme während der polarographischen Untersuchung zu überprüfen.