Electrooxidation of the antiviral drug valacyclovir and its square-wave and differential pulse voltammetric determination in pharmaceuticals and human biological fluids

The electrochemical properties of valacyclovir, an antiviral drug, were investigated in pH range 1.8-12.0 by cyclic, differential pulse and square-wave voltammetry. The drug was irreversibly oxidized at a glassy carbon electrode in one or two oxidation steps, which are pH-dependent. For analytical purposes, a very resolved diffusion controlled voltammetric peak was obtained in Britton-Robinson buffer at pH 10.0 using differential pulse and square-wave modes. Limits of detection were 1.04 × 10⁻⁷ and 4.60 × 10⁻⁸ M for differential pulse and square-wave voltammetry, respectively. The applicability to direct assays of tablets, spiked human serum and simulated gastric fluid, was described.     

Determination of ciclazindol in biological fluids by differential pulse polarography

A differential pulse polarographic method has been developed for determination of the antidepressant, 10-(m-chlorophenyl)-2,3,4,10-tetrahydropyrimido[1,2a]indol-10-ol hydrochloride in plasma and urine. The method involves solvent extraction of the drug from the plasma or urine, evaporation to dryness and dissolution of the residue in 10% methanolic 0.01 M tetraethylammonium chloride solution followed by differential pulse polarography. The mean recovery of the drug from plasma containing 0.5–5.0 μg ml^-1 is 80%; the coefficient of variation is 5.5% at the 1.0-μg ml^-1 (2.98 × 10^-6 M) level on 2-ml samples. The method is not subject to interference from the chemical degradation products and metabolites. The techniques described have been applied to the analysis of human plasma; the polarographic and gas Chromatographic results showed good agreement.     

Electrooxidation of pimozide and its differential pulse voltammetric and HPLC-EC determination

The oxidative behaviour of pimozide was studied in hydroalcoholic media (10+90 methanol-H₂O, pH range 2-7.5) at carbon based electrodes. Pimozide was irreversibly oxidized at high positive potentials, resulting in the formation of a couple with a reduction and re-oxidation peak at much lower potentials. The response was evaluated with respect to pH, scan rate, addition of surfactant and other variables. Using differential pulse voltammetry (DPV), the drug yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 2.1 at +1.1 V (versus Ag/AgCl) on glassy carbon electrode. The process could be used to determine pimozide concentrations in the range 8×10⁻⁷-1×10⁻⁴ M. Applicability to tablets and human serum analysis was illustrated. Furthermore, a high-performance liquid chromatographic method with electrochemical detection (HPLC-EC) was developed, which allowed pimozide to be detected down to a level of 2.7×10⁻¹⁰ M (0.25 ppb).     

Determination of 1,4-benzodiazepines in biological fluids by differential pulse polarography

The determination of various 1,4-benzodiazepines and their metabolites by differential pulse polarography is reviewed and compared with that by other methods, and the general applicability of the polarographic methods, in terms of simplicity and flexibility, is demonstrated.     

Differential pulse polarographic determination of ofloxacin in pharmaceuticals and biological fluids

A sensitive method is described for the determination of ofloxacin in its pure form, dosage forms and biological fluids. The proposed method depends upon the polarographic activity of ofloxacin in Britton Robinson buffers, whereby a well-defined cathodic wave is produced over the pH range 4.1-10.3. The wave was characterized as being irreversible, diffusion-controlled with limited adsorption properties. The current-concentration relationship was found to be rectilinear over the range 5x10(-5)-5x10(-4) M and 1x10(-5)-5x10(-4) M using the DC(t) and DPP modes respectively, with a minimum detectability (S/N=3) of 3x10(-7) M. The proposed method was successfully applied to the determination of ofloxacin in tablets and biological fluids. The results obtained were found to be in agreement with those obtained by a reference method.     

Differential pulse voltammetric determination of famotidine

A differential pulse voltammetric method for the determination of famotidine in pharmaceutical preparations is described. The method is based on electrochemical oxidation of famotidine at a glassy carbon or platinum electrode. The proposed method shows good reproducibility, and sample preparation is simple.     

Anodic voltammetric behavior and determination of cefixime in pharmaceutical dosage forms and biological fluids

The voltammetric behavior of cefixime was studied using cyclic, linear sweep, differential pulse and square wave voltammetric techniques. The oxidation of cefixime was irreversible and exhibited diffusion controlled process depending on pH. The oxidation mechanism was proposed and discussed. Different parameters were tested to optimize the conditions for the determination of cefixime. The dependence of current intensities and potentials on pH, concentration, scan rate, nature of the buffer was investigated. According to the linear relationship between the peak current and the concentration, differential pulse (DPV) and square wave (SWV) voltammetric methods for cefixime assay in pharmaceutical dosage forms and biological fluids were developed. For the determination of cefixime were proposed in acetate buffer at pH 4.5, which allows quantitation over the 6 × 10⁻⁶-2 × 10⁻⁴ M range in supporting electrolyte and spiked serum sample; 8 × 10⁻⁶-2 × 10⁻⁴ M range in urine sample; 6 × 10⁻⁶-1 × 10⁻⁴ M range in breast milk samples for both techniques. The repeatability, reproducibility, precision and accuracy of the methods in all media were investigated. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage forms and in the biological samples, respectively.     

A direct differential pulse anodic stripping voltammetric method for the determination of thallium in natural waters

A dual direct method for the ultratrace determination of thallium in natural waters by differential pulse anodic stripping voltamrnetry (d.p.a.s.v.) is presented. D.p.a.s.v. at the hanging mercury drop electrode and at the mercury film electrode is used in the concentration ranges 0.5–100 μg Tl l^-1, and 0.01–10 μg Tl l^-1, respectively. Quantification is aided by the technique of standard additions. The response of the method is optimized for typical natural surface water matrices. An intercomparison of thalium determinations performed by the two anodic stripping methods and electrothermal-atomization atomic absorption spectrometry on normal and thallium-spiked surface water samples demonstrates equivalent accuracy within the range where atomic absorption is applicable. The method appears free from serious interferences.     

Electrochemical behavior and differential pulse voltammetric determination of paracetamol at a carbon ionic liquid electrode

The electrochemical behavior of paracetamol in 0.1 M acetate buffer solution (pH 4.6) was investigated at a traditional carbon paste electrode (TCPE) and a carbon ionic liquid electrode (CILE) fabricated by replacing nonconductive organic binders with a conductive hydrophobic room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF₆). The results showed that the CILE exhibited better reversibility for the electrochemical redox of paracetamol. The oxidation potential of paracetamol at the CILE is +0.462 V, which is approximately 232 mV lower than that at the TCPE; the oxidation peak current response is nine times higher than that at the TCPE. The differential pulse voltammetric determination of paracetamol at the CILE was established based on this behavior. After optimizing several important parameters controlling the performance of paracetamol at the CILE, the oxidation peak current versus paracetamol concentration at the CILE showed linearity in the range from 1.0 μM to 2.0 mM (R ²  = 0.9992) with a detection limit of 0.3 μM (S/N = 3). The method has been applied to the determination of paracetamol in tablets and urine samples and the average recovery of paracetamol was 98.5% and 99.3%, respectively. The proposed CILE showed good sensitivity and reproducible response without influence of interferents commonly existing in pharmaceutical and urine samples. Figure CV curves of paracetamol illustrate the enhanced electrochemical behavior of paracetamol at the CILE (b), which forms the basis for the differential pulse voltammetric determination of paracetamol     

Differential pulse voltammetric determination of uranium in low concentration streams

A differential pulse voltammetric method has been successfully used for the determination of uranium in low concentration streams of a uranium plant. The method gives a precision of about 13% to 7% in the range of 300 ppb to 15 ppm. The accuracy of the results was ascertained by comparing the values with those obtained by a spectrophotometric method. The method is simple, fast, sensitive, fairly accurate and does not require a preconcentration step.     

Behaviour of solid electrodes in normal and differential pulse voltammetric methods

In order to investigate the behaviour of solid electrodes in normal and differential pulse voltammetry, step functions have been applied to the electrochemical cell containing the electrodes to be tested, in the absence of electroactive species. The large residual current observed could be attributed to electrochemical reactions of the electrode material.     

Simultaneous voltammetric determination of prednisone and prednisolone in human body fluids

A sensitive, rapid and reliable electrochemical method based on voltammetry at single wall carbon nanotube (SWNT) modified edge plane pyrolytic graphite electrode (EPPGE) is proposed for the simultaneous determination of prednisolone and prednisone in human body fluids and pharmaceutical preparations. The electrochemical response of both the drugs was evaluated by osteryoung square wave voltammetry (OSWV) in phosphate buffer medium of pH 7.2. The modified electrode exhibited good electrocatalytic properties towards prednisone and prednisolone reduction with a peak potential of ∼−1230 and ∼−1332 mV respectively. The concentration versus peak current plots were linear for both the analytes in the range 0.01-100 μM and the detection limit (3σ/slope) observed for prednisone and prednisolone were 0.45 × 10⁻⁸, 0.90 × 10⁻⁸ M, respectively. The results of the quantitative estimation of prednisone and prednisolone in biological fluids were also compared with HPLC and the results were in good agreement.     

Anodic oxidation of etodolac and its square wave and differential pulse voltammetric determination in pharmaceuticals and human serum

A voltammetric study of the oxidation of etodolac has been carried out at the glassy carbon electrode. The electrochemical oxidation of etodolac was investigated by cyclic, linear sweep, differential pulse and square wave voltammetry using glassy carbon electrode. Different parameters were tested to optimize the conditions for the determination of etodolac. The dependence of intensities of currents and potentials on pH, concentration, scan rate, nature of the buffer was investigated. For analytical purposes, a very well resolved diffusion controlled voltammetric peak was obtained in Britton-Robinson buffer at pH 2.15 for differential pulse and square wave voltammetric techniques. The linear response was obtained in the ranges of 2.10(-6)-8.10(-5) M with a detection limit of 6.8x10(-7) and 6x10(-6)-8x10(-5) M with a detection limit of 1.1x10(-6) M for differential pulse and square wave voltammetric techniques, respectively. Based on this study, simple, rapid, selective and sensitive two voltammetric methods were developed for the determination of the etodolac in tablet dosage form and human serum.     

Spectrophotometric determination of proteins in biological fluids

A comparative analysis of procedures of the spectrophotometric determination of total protein with various organic dyes, Bromocresol Green, Bromophenol Blue, and Pyrogallol Red, in biological fluids is presented. It is shown that the results of determination with various dyes can differ because of the specific features of reagent interaction with the components of biological fluids. A new organic reagent, Bromopyrogallol Red, possessing equal sensitivity to different protein fractions (albumins and globulins) and ensuring a minimum error of the determination of total protein in clinical examinations using calibration solutions of various compositions is proposed. A procedure for the determination of total protein in biological fluids is developed and tested on real samples of urine and blood serum.     

Spectrofluorimetric determination of proguanil in biological fluids

A spectrofluorimetric method for proguanil in biological fluids is described based on the reaction of proguanil with 9-fluorenecarboxylic acid chloride and measurement of the resulting s-triazine derivative. The limits of detection for proguanil in methanol, water, plasma, urine and saliva are 1.5, 5.1, 7.6, 4.2 and 11.9 ng ml^?1, respectively. Preliminary results for proguanil levels in plasma and saliva following a single 100-mg oral dose are reported.     

Development of a differential pulse voltammetric method for the determination of Silymarin/Vitamin E acetate mixture in pharmaceuticals

Differential pulse voltammetric method was developed for determination of Silymarin (SMR)/Vitamin E acetate (VEA) mixture in pharmaceuticals. SMR and VE gave well-resolved diffusion-controlled anodic peaks at +756 and +444mV, respectively (versus Ag/AgCl) in Britton-Robinson buffer at pH 2.8. The solution conditions and instrumental parameters were optimized for their quantitative determination. The linear response was obtained in the range 0.1-4.0mgL(-1) with a detection limit of 0.03mgL(-1) for SMR and 0.05-4.0mgL(-1) with a detection limit of 0.01mgL(-1)for VEA.     

Simultaneous voltammetric determination of molybdenum and copper in biological samples

 A selective, sensitive and reliable voltammetric method for the simultaneous determination of Cu and Mo is developed. Both metals form complexes with 8-hydroxyquinoline (oxine). Mo gives two reduction peaks with oxine in acidic chloride media at −0.52 V and −0.58 V, while copper exhibits only one at −0.14 V. Common heavy metals do not interfere at all. The limit of detection is 0.29 ng/ml for Mo and 0.14 ng/ml for Cu after preconcentration on the hanging mercury drop electrode for 30 s at −0.2 V. The R.S.D. at a concentration level of 10 ng/ml is 3.8% for Cu and 5.3% for Mo. The method is applied to different biological samples. Received: 15 January 1996/Revised: 11 April 1996/Accepted: 16 April 1996     

Simultaneous voltammetric determination of morphine and noscapine by adsorptive differential pulse stripping method and least-squares support vector machines

An adsorptive differential pulse stripping method for the simultaneous determination of morphine and noscapine is proposed. The procedure involves an adsorptive accumulation of morphine and noscapine on a hanging mercury drop electrode (HMDE), followed by oxidation of adsorbed morphine and noscapine by voltammetric scan using differential pulse modulation. The optimum experimental conditions are: pH 10.0, accumulation potential of −100 mV versus Ag/AgCl, accumulation time of 150 s, scan rate of 40 mV s⁻¹ and pulse height of 100 mV. Morphine and noscapine peak currents were observed in same potential region at about +0.25 V. The simultaneous determination of morphine and noscapine by using voltammetry is a difficult problem in analytical chemistry, due to voltammogram interferences. The resolution of mixture of morphine and noscapine by the application of least-squares support vector machines (LS-SVM) was performed. The linear dynamic ranges were 0.01-3.10 and 0.015-2.75 μg mL⁻¹ and detection limits were 3 and 7 ng mL⁻¹ for morphine and noscapine, respectively. The capability of the method for the analysis of real samples was evaluated by the determination of morphine and noscapine in addict's human plasma with satisfactory results.     

Study on the electrochemical behavior and differential pulse voltammetric determination of rhein using a nanoparticle composite film-modified electrode

A sensitive electrochemical method was developed for the differential pulse voltammetric determination of rhein at a glassy carbon electrode (GCE) modified with a nanoparticle composite film. In the present paper, multi-wall carbon nanotube (MWNT) was dispersed into dihexadecyl phosphate (DHP) to give a homogeneous suspension. After the solvent evaporation, a uniform film of MWNT-DHP composite film was obtained on the GCE surface. The MWNT-DHP composite film-modified GCE exhibited excellent electrocatalytic behavior toward the redox of rhein. Compared with an irreversible reduction of rhein at the bare GCE, a reversible redox behavior of rhein was observed at the MWNT-DHP composite film-modified GCE and the redox current was also enhanced greatly. Based on this, a cathodic differential pulse voltammetry (DPV) was applied for the determination of rhein. The experimental parameters, which influence the current of rhein, were optimized. Under optimal conditions, the cathodic DPV measurements were performed and a linear response of rhein was obtained in the range from 1.0 x 10(-8) to 5.0 x 10(-6) mol L(-1) and with a limit of detect (LOD) of 5.0 x 10(-9) mol L(-1). The proposed procedure was successfully applied to assay rhein in real samples with satisfactory results.     

Determination of chlorpromazine and thioridazine by differential pulse voltammetry in acetonitrile medium

This work describes optimal conditions for the determination of chlorpromazine and thioridazine by DPV, with a detection limit of 4.0 x 10(-7)M (0.16 microg/ml). The well-defined peaks indicate that direct measurement in a medium of 0.03 M perchloric acid in acetonitrile is possible and the use of DPV is advantageous when small amounts are to be determined. The sample procedure for pharmaceutical tablets is simple and fast. The method is useful for control of the quality and purity of phenothiazine drugs. The possibility of using numerical analysis to resolve composite signals of the compounds studied has also been demonstrated.