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Compared to other voltammetric techniques a square wave voltammetry (SWV), which is presented in this minireview, has a several advantages such as high speed, increased analytical sensitivity and relative insensitivity to the presence of dissolved oxygen. Also it is an electrochemical technique used in analytical applications and fundamental studies of electrode mechanism. This paper delivers both the underlying theory and the practical guidance needed to apply square wave techniques and also provides a wide collection of data for the description of diverse tendencies that characterize several electrochemical reactions analyzed by SWV. This review summarizes some of the recent developments and application of direct and stripping SWV for drug compounds in their dosage forms and biological samples as reported in the period from 1997 till 2010 year.

Ziprasidone is a psychotropic agent used for the treatment of schizophrenia. Its oxidation was investigated electrochemically at boron-doped diamond and glassy carbon electrodes using cyclic, differential pulse, and square wave voltammetry. The dependence of the peak current and peak potentials on pH, concentration, nature of the buffer, and scan rate were examined. The process was diffusion and adsorption controlled for boron-doped diamond and glassy carbon electrodes, respectively. The possible mechanism of oxidation was discussed with some model compounds that have indole and piperazine oxidations. A linear response was obtained between 8 × 10-7 and 8 × 10-5 M for the first peak in acetate buffer (pH 5.5) and between 2 × 10-6 and 2 × 10-4 M for the second peak in 0.1 M H2SO4 with boron-doped diamond electrode for differential pulse and square wave voltammetric techniques. The reproducibility and accuracy of the proposed methods were found between 0.31 and 1.20, 99.27 and 100.22, respectively. The recovery studies were also achieved to check selectivity and accuracy of the methods. The proposed methods were applied for the determination of ziprasidone from pharmaceutical dosage forms and human serum samples without any time-consuming extraction, separation, evaporation or adsorption steps prior to drug assay except precipitation of the proteins using acetonitrile. The results were statistically compared with those obtained through an established LC-UV technique, no significant differences were been found between the voltammetric and LC methods. © 2010 Elsevier B.V. All rights reserved.

The electrooxidative behavior and determination of opipramol, a tricyclic compound for therapy of anxious-depressive states and general anxiety disorder, were investigated at a glassy carbon electrode using cyclic, linear sweep, differential pulse and Osteryoung square wave voltammetric techniques. The oxidation of opipramol was irreversible and exhibited a diffusion controlled process dependent on pH using a glassy carbon electrode. The oxidation mechanism on a glassy carbon electrode is proposed and discussed. The anodic process can be attributed to the oxidation of azepine and piperazine rings. Different parameters were tested to optimize the conditions for the determination of opipramol. The dependence of current intensities and potentials on pH, concentration, scan rate, and nature of the buffer was investigated as detailed. Opipramol in pH 3.7 acetate buffer presents a well-defined anodic response at + 0.86 V according to studies of the proposed method. The determination of opipramol was in...

The anodic behavior and determination of pefloxacin on boron-doped diamond and glassy carbon electrodes were investigated using cyclic, linear sweep, differential pulse and square wave voltammetric techniques. In cyclic voltammetry, pefloxacin shows one main irreversible oxidation peak and additional one irreversible ill-defined wave depending on pH values for both electrodes. The results indicate that the process of pefloxacin is irreversible and diffusion controlled on boron-doped diamond electrode and irreversible but adsorption controlled on glassy carbon electrode. The peak current is found to be linear over the range of concentration 2 × 10 −6 to 2 × 10 −4 M in 0.5 M H 2 SO 4 at about +1.20 V (versus Ag/AgCl) for differential pulse and square wave voltammetric technique using boron-doped diamond electrode. The repeatability, reproducibility, precision and accuracy of the methods in all media were investigated. Selectivity, precision and accuracy of the developed methods were also checked by recovery studies. The procedures were successfully applied to the determination of the drug in pharmaceutical dosage forms and humans serum samples with good recovery results. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage forms and biological samples, respectively.

Voltammetric and liquid chromatographic (LC) methods have been developed for the simultaneous determination of amlodipine besylate (AML) and rosuvastatin calcium (ROS) for the first time. Detailed electrochemical behavior and simultaneous voltammetric determination of AML and ROS were investigated in detail using glassy carbon electrode (GCE). High-performance liquid chromatography (HPLC) and ultra-performance liquid chromatography (UPLC) were also developed for the comparison. Voltammetric method exhibited linear dynamic responses for the simultaneous assay of AML and ROS in the concentration range between 0.006 and 2.85 μg/mL and between 0.01 and 5.00 μg/mL, with detection limits of 0.001 and 0.003 μg/mL, respectively. On the other hand, LC methods presented a wider linearity range than that of the SWV method between 0.5 and 100 μg/mL with the detection limits of 0.011 and 0.027 μg/mL for AML and 0.034 and 0.042 μg/mL for ROS by UPLC and HPLC techniques, respectively.

Abacavir (I), a drug used in the treatment of HIV, is electrochemically reduced at the dropping mercury electrode in a four-electron process, similar to structurally related adenine (III) and adenosine triphosphate (IV). To undergo the reduction, the species is protonated in the vicinity of the electrode. The protonations take place on the 6-amino group and on one of the pyrimidine ring nitrogens. The role of covalent hydration of the pyrymidine ring has been interpreted. Best suited as supporting electrolytes for analytical purposes are solutions of 0.1-1.0 M sulfuric, perchloric, or hydrochloric acids. Procedures of analyses of tablets containing I were established and validated, based on peak currents obtained by linear sweep, differential pulse, or square-wave voltammetry with a hanging mercury drop electrode as indicator electrode. The procedure proved to be more sensitive and more reliable than that based on oxidation on a glassy carbon electrode, proposed previously.

Boron-doped diamond electrodes have received much attention for electrochemical determination due to their attractive electrochemical properties over other electrodes. The electrooxidation of fluvastatin sodium at boron-doped diamond electrode was investigated using cyclic, differential pulse and square wave voltammetry. The possible mechanism of oxidation was discussed with model compounds that have indole oxidation. The dependence of the peak current and potentials on pH, concentration, scan rate, and the nature of the buffer were investigated. The oxidation of fluvastatin was irreversible and exhibited a diffusion-controlled fashion. The slope of the log i p –log v linear plot was 0.44 indicating the diffusion control for pH 10.00 Britton–Robinson buffer solution. The linear response was obtained in the ranges of 1 × 10 − 6 M–6 × 10 − 4 M in pH 10.00 BR buffer solution. The detection limit of the standard solution is estimated to be 1.37 × 10 − 7 M for DPV, 1.44 × 10 − 7 M for SWV. The repeatability of the methods was found as 0.66 and 0.15 RSD % for peak currents for differential pulse and square wave voltammetry, respectively. The practical analytical value of the method is demonstrated by quantitative determination of fluvastatin in pharmaceutical formulation and human serum, without the need for separation or complex sample preparation, since there was no interference from the excipients and endogenous substances. Selectivity, reproducibility and accuracy of the developed methods were demonstrated by recovery studies.

The electrochemical behavior of atorvastatin calcium at glassy carbon and boron-doped diamond electrodes has been studied using voltammetric techniques. The possible mechanism of oxidation was discussed with model compounds. The dependence of the peak current and potentials on pH, concentration, scan rate and nature of the buffer were investigated for both electrodes. The oxidation of atorvastatin was irreversible and exhibited a diffusion-controlled fashion on the diamond electrode. A linear response was obtained within the range of 9.65 x 10(-7) - 3.86 x 10(-5) M in 0.1 M H(2)SO(4) solution for both electrodes. The detection limits of a standard solution are estimated to be 2.11 x 10(-7) M with differential pulse voltammetry (DPV) and 2.05 x 10(-7)M with square wave voltammetry (SWV) for glassy carbon electrode, and 2.27 x 10(-7) M with DPV and 1.31 x 10(-7)M with SWV for diamond electrodes in 0.1 M H(2)SO(4) solution. The repeatability of the methods was found good for both electrodes. The methods were fully validated and successfully applied to the high-throughput determination of the drug in tablets, human serum and human urine with good recoveries.

A rapid, sensitive, and specific reverse phase high performance liquid chromatography with diode array detection procedure for the simultaneous determination of abacavir, efavirenz and valganciclovir in spiked human serum is described. Separation was performed on a 5 μm Waters Spherisorb column (250 × 4.6 mm ID) with acetonitrile: methanol:KH2PO4 (at pH 5.00) (40:20:40 v/v/v) isocratic elution at a flow rate of 1.0 mL min−1. Calibration curves were constructed in the range of 50–30,000 ng mL−1 for abacavir and efavirenz, and 10–30,000 ngmL−1 for valganciclovir in serum samples. The limit of detection and limit of quantification concentrations of the HPLC method were 3.80 and 12.68 ng mL−1 for abacavir, 2.61 and 8.69 ng mL−1 for efavirenz, 1.30 and 4.32 ng mL−1 for valganciclovir. The method has been applied, without any interference from excipients or endogenous substances, for the simultaneous determination of these three compounds in human serum.

This paper describes the validation of an isocratic high-performance liquid chromatographic method for the assay of valganciclovir in raw materials, tablets and human serum samples. Valganciclovir and fluvastatin (internal standard) were well separated using a reversed phase column and a mobile phase consisting of a mixture of acetonitrile:methanol:KH2PO4 (0.02 M) (40:20:40; v/v/v) (at pH 5.0). The mobile phase was pumped at 1.0 mL min−1 flow rate and valganciclovir was detected by diode-array detection at 255 nm. The retention times for valganciclovir and fluvastatin were 3.41 and 5.60 min, respectively. A linear response (r > 0.999) was observed in the range of 10–30,000 ng mL−1 in mobile phase and serum. The limit of detection and limit of quantification were found as 2.95 and 9.82 ng mL−1 in mobile phase and 1.73 and 5.77 ng mL−1 in human serum samples, respectively. Validation parameters as precision, accuracy, selectivity, reproducibility and system suitability tests were also determined. The method can be used for valganciclovir assay of tablets and human serum samples as the method separates valganciclovir from tablet excipients and endogenous substances.

The polarographic reduction of Co(II) in the presence of moxifloxacin (1-cyclopropyl-7-[(S,S)-2.8-diazabicyclo[4.3.0]non-8-yl]-6-fluoro-8-methoxy-1.4-dihydro-4-oxo-3-quinolinecarboxylic acid) gives rise to an additional adsorption peak corresponding to the reduction of Co(II)-moxifloxacin complex on the mercury drop electrode at -1.17 V. This new peak is applicable to Co(II) determination with the linearity proportional to the Co(II) concentration in the range of 4.93 x 10(-7) -6.90 x 10(-5) M and can be attributed to an adsorption-controlled process with an irreversible reduction. Without using moxifloxacin, the polarographic determination of 2.50 x 10(-6) M Co(II) is impossible under the given conditions due to very poor sensitivity at -1.38 V. The proposed method showed good precision and accuracy with a relative standard deviation of 3.01% and relative error of +6.40% for the determination of 2.50 x 10(-6) M Co(II) next to 5.0 x 10(-6) M of Zn(II), Ni(II), and Cd(II). The accuracy of the method was also checked by the determination of Co(II) spiked with tap water and certified sea water, and the percentage recoveries were 97.5 and 96.7%, respectively (n = 4 at 95% confidence interval).

A simple, accurate, precise and fully automated method for the simultaneous determination of abacavir, lamivudine and zidovudine in pharmaceutical tablets, human serum samples and drug dissolution studies has been developed. Separation was performed on a 5 μm Zorbax® C18 column (150 × 4.6 mm ID) with methanol:water:phosphate buffer at pH 5.65 (80:10:10; v/v/v) isocratic elution in less than 7 min with a flow rate of 0.6 mL min−1.Good sensitivity for all analytes was observed with UV detection at 275 nm. The method allowed quantitation over the 500–3,000 ng mL−1 range for abacavir and 500–5,000 ng mL−1 range for lamivudine and zidovudine. The method has been applied, without any interference from excipients or endogenous substances, for the simultaneous determination of these three compounds in tablets. Human serum and drug dissolution studies.

Carbon and its derivatives, as the high performance material, occupy a special place in electrochemistry due to its ‐in many ways‐ extreme properties. Recent trends and advances in the electrochemistry of carbon‐based electrodes are reviewed. The varieties of carbon‐based electrodes, their basic physicochemical properties and some characteristics are surveyed. Special attention is paid to the possibilities of carbon‐based electrodes in electroanalytical investigation in pharmaceutical dosage forms and biological samples using modern electrochemical techniques. This review includes a summary of the rules that must be considered for drug analysis from its dosage forms and biological samples using carbon‐based electrodes. The present review is the first comprehensive report on the heterogeneous and homogeneous carbon electrodes, and an addition to many excellent reviews on carbon electrodes in the literature. This review summarizes some of the recent developments and applications of carbon‐based ele...

Ascorbic acid is the most common electroactive biological compound found in some plant species (e.g., Citrus species, Rosa species). The electrochemical oxidation of ascorbic acid was investigated by cyclic, linear sweep, differential pulse (DPV), and square wave (SWV) voltammetry. For analytical purposes, a very well-resolved diffusion-controlled voltammetric peak was obtained in acetate buffer at pH 3.50 for DPV and SWV. The linear response was obtained in the range of 3.52–176.1 μg/mL with a detection limit of 0.88 μg/mL for DPV and 0.52 µg/mL for SWV. Based on this study, simple, rapid, selective, and sensitive voltammetric methods were developed for the determination of ascorbic acid in pharmaceutical dosage forms and Rosa species (R. dumalis ssp. boissieri var. boissieri, R. canina, R. pulverulenta, R. heckeliana ssp. vanheurckiana, and R. montana subsp. woronowii). The results obtained are compared with the HPLC data. The developed methods enable the extracts to be analyzed without the necessity of any time-consuming separation.

Native and denatured states of bovine serum albumin (BSA) were studied by d.c. polarographic and voltammetric Brdicka catalytic responses (BCR) in cobalt-containing solution and by constant current chronopotentiometric stripping analysis (CPSA) in borate buffer, pH 9.3. We found that 90 nM denatured BSA produced catalytic peak H (around − 1.8 V vs. Ag/AgCl/3 M KCl). This peak was about 50-fold higher than the native protein under the same conditions. Qualitatively similar results were obtained also with other proteins in native and denatured states, such as human serum albumin, γ-globulin, myoglobin and α-crystallin. 2 nM denatured BSA produced a well-developed CPS peak (at accumulation time 5 min) while native BSA yielded almost no signal under the same conditions.

WOS: 000237841500017, A capillary electrophoretic method was described for the determination of droperidol in pharmaceutical tablets and human serum. Droperidol and internal standard, lansoprazole, were separated on an uncoated fused-silica capillary using a run buffer containing borate (10 mM; pH 9.3) and aqueous methanol (20%, v/v). The signals were detected at 210 nm. The migration times for droperidol and internal standard were 2.1 and 2.9 min, respectively. The method has been validated in the range of 2.2 x 10(-5) - 7.8 x 10(-5) M and applied to both tablets and human serum with good repeatability and no interference.

The electrooxidative behaviour and determination of quetiapine (QTP), a dibenzothiazepine derivative and antipsychotic agent, on a glassy carbon disc electrode was investigated using cyclic (CV), linear sweep (LSV), differential pulse (DPV) and Osteryoung square wave voltammetry (OSWV). Fully validated DP and SW voltammetric procedures are described for the determination of QTP. QTP in pH 3.5 acetate buffer solution presents a well-defined anodic response, studied by the proposed methods. This main response was due to the irreversible, diffusion-controlled, one-electron and one-proton oxidation of the aliphatic nitrogen of the piperazine ring. Under optimal conditions, a detection limit of 4.0 × 10−8 mol L−1 for DPV and 1.33 × 10−7 mol L−1 for OSWV, and a linear calibration graph in the range from 4.0 × 10−6 to 2.0 × 10−4 mol L−1 were obtained for both methods. The procedure was successfully applied to the determination of the drug in tablets, human serum and human urine with good recoveries. The detection limits were 6.20 × 10−7 mol L−1 and 5.92 × 10−7 mol L−1 in human serum and 1.44 × 10−7 mol L−1 and 1.31 × 10−6 mol L−1 in human urine, for the DPV and OSWV method, respectively.

The voltammetric behavior of vardenafil was studied on glassy carbon electrode using cyclic, differential pulse (DPV) and Osteryoung square-wave (OSW) voltammetric techniques. Vardenafil exhibited irreversible anodic waves over the pH range 1.00–12.00 in different supporting electrolytes. The current–concentration plot was rectilinear over the range from 4 × 10−7 to 2 × 10−5 M with correlation coefficient of 0.999. The wave was characterized as being irreversible and diffusion-controlled. The developed procedure was successfully applied to the determination of vardenafil in tablets and in spiked human serum. Furthermore, results obtained by the proposed method have been compared with high-performance liquid chromatographic method.

Lamivudine (LAM) is a synthetic nucleoside analogue with activity against human immunodeficiency virus-type 1 (HIV-1) and Hepatitis B virus (HBV). The aim of this study was to determine LAM levels in serum and pharmaceutical formulations, by means of electrochemical methods using hanging mercury drop electrode (HMDE). On this electrode, LAM undergoes irreversible reduction at the peak potential near Ep−1.26 V (vs. Ag/AgCl/3 M KCl). Reduction LAM signals were measured by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square-wave voltammetry (OSW). DPV and OSW techniques for the determination of LAM in acetate buffer at pH 4.5, which allows quantitation over the 4×10−6 to 1×10−4 M range in supporting electrolyte for both methods, were proposed. The linear response was obtained in acetate buffer in the ranges of 2×10−6 to 2×10−4 M for spiked serum samples at pH 4.5 for both techniques. The repeatability and reproducibility of the methods for all media were determined. The standard addition method was used in serum. Precision and accuracy were also checked in all media. No electroactive interferences from the endogenous substances were found in serum. With respect to side effects of high doses and short half-life of LAM, a fast and simple detection method is described in this study.

The electrochemical reduction behavior of mefloquine HCl (MEF), the antimalarial drug, was studied in aqueous alcoholic media at a hanging mercury drop electrode. Cyclic voltammetric studies showed one well-defined reduction peak and one ill-defined reduction wave between pH 1.5 and 12.03. The reduction was found as irreversible or quasireversible depending on pH and exhibited diffusion controlled process. The mechanism of reduction process was discussed. A systematic study of the experimental parameters that affect the differential pulse and square wave response was carried out and the optimized experimental conditions were obtained. The calibration plots were derived for the determination of MEF in pharmaceutical dosage forms and biological samples. DPV and SWV techniques for the determination of MEF in Britton–Robinson buffer at pH 11.10, which allows quantitation over the 6×10−6 to 8×10−5 M range in the supporting electrolyte, were proposed. The linear response was obtained in samples in the ranges of 6×10−6 to 6×10−5 M for both techniques. These methods are fully validated. The standard addition method was used in the biological media. No electroactive interferences from the excipients and endogenous substances were found in tablets and biological fluids.

A simple and rapid electrochemical method for the determination of ganciclovir in human serum and pharmaceutics was developed. The anodic peak at +1.15 V obtained in a buffer on glassy carbon electrode was used for analysis. The peak current and peak potential depends on pH, scan rate and initial potential. Decrease of the anodic peak with increasing pH, as well as deviations from linear plots of i p = f ( C ) and i p = k v 1 / 2 indicate that this peak at higher concentrations is affected by adsorption–desorption phenomena. At concentrations lower than about 1 × 10 −4 M the peak current obtained by differential pulse and square wave voltammetry is practically a linear function of concentration and is suitable for quantitative determination in pharmaceutical dosage forms and human serum. The linear response was obtained in the ranges of 1 × 10 −6 –1 × 10 −4 M give detection limit on one decimal point: 8.1 × 10 −8 M for DPV and 4.52 × 10 −8 M for SWV techniques. The similarly repeatability of the methods was within 1.40–1.05% for peak currents and 0.19–0.11% for peak potentials for DPV and SWV, respectively. Precision and accuracy of the developed method was checked by recovery studies.

Flupenthixol hydrochloride (FLP) has an antipsychotic activity against depression and is irreversible oxidizable at the glassy carbon electrode in various buffer systems and at different pH values. The mechanism of the oxidation process was discussed. According to the linear relation between the peak current and FLP concentration, differential pulse and square wave voltammetric methods for its determination in pharmaceutical dosage forms and spiked human serum samples were developed. For analytical purposes, a very well resolved diffusion controlled voltammetric peak was obtained in Britton‐Robinson buffer at pH 7.02 (20% methanol) at 0.75 and 0.79 V for differential pulse and square wave voltammetric techniques, respectively. The linear response was obtained in the ranges of 8 × 10−7 to 1 × 10−4 M with a detection limit of 1.17 × 10−7 M for differential pulse and 1 × 10−6 to 1 × 10−4 M with a detection limit of 2.86 × 10−7 M for square wave voltammetric techniques. The repeatability and reproduc...

Abacavir has an antiretroviral activity against HIV and is oxidizable at the glassy carbon electrode. Cyclic voltammetry studies showed one well-defined oxidation wave or splitted two waves depending on pH. The oxidation was irreversible and exhibited diffusion controlled process depending on pH. The mechanism of the oxidation process was discussed. According to the linear relation between the peak current and the concentration, differential pulse voltammetric (DPV) and square wave voltammetric (SWV) methods for its quantitative determination in pharmaceutical dosage forms and biological fluids were developed. These two voltammetric techniques for the determination of abacavir in Britton–Robinson buffer at pH 2.0, which allows quantitation over the 8×10 −7 to 2×10 −4 M range in supporting electrolyte for both methods were proposed. The linear response was obtained in Britton–Robinson buffer in the ranges of 1×10 −5 to 1×10 −4 M for spiked urine sample at pH 2.0 and 2×10 −5 to 2×10 −4 M for spiked serum samples at pH 3.0 for both techniques. The repeatability and reproducibility of the methods for all media (such as supporting electrolyte, serum and urine samples) were determined. Precision and accuracy were also checked in all media. The standard addition method was used in biological media. No electroactive interferences from the endogenous substances were found in the biological fluids.

In aqueous solutions containing 30% (v/v) acetonitrile the unprotonated form of the piperazine ring of sildenafil (I) is oxidized on a glassy carbon electrode between pH 2 and 8. Whereas citrate anions under conditions used are not oxidized, the oxidation pattern of sulfonamides differs from that of sildenafil (I). On the other hand, the oxidation of I resembles that of the oxidation of piperazine ring in nefazodone (III) and trazodone (IV). A more positive peak of sildenafil corresponds to an adsorption–desorption process. Measurement of the peak current enables rapid determination of sildenafil (I) in pharmaceutical preparations with sufficient accuracy.

Two new spectral approach (graphical and chemometric techniques) were applied for resolution of a binary mixture of valsartan (VST) and hydrochlorothiazide (HCT) in tablets without a separation procedure. In the ratio derivative spectrophotometry, analytical derivative amplitudes were measured at 231.5 and 260.5 nm for VST and at 270.6 nm for HCT in the first derivative of the ratio spectra. The calibration graphs follow Beer's law in the ranges of 8–24 µg mL−1 for VST and 2–10 µg mL−1 for HCT. The prepared calibrations for the first technique were tested for the synthetic binary mixtures of both drugs. Mean recoveries and relative standard deviations were found as 100.4% and 1.76% for VST, 102.5% and 2.41% for HCT, respectively. In the inverse least‐square technique, absorbances matrix were produced by measurements in the spectral range from 225 to 280 nm of the interval of Δλ = 5 nm at 12 wavelengths in zero order spectra of the various binary mixtures. The prepared calibration set for the abso...

The electrooxidative behavior and determination of Tamsulosin HCl (TAM), one of the alpha(1)-adrenoceptor antagonist, on a glassy carbon disc electrode were investigated for the first time by using cyclic, linear sweep, differential pulse (DPV) and square wave voltammetry (SWV). TAM showed an irreversible oxidation behavior at all pH values and buffers studied. From the electrochemical response, the main oxidation step was found to be related to the methoxy group on the phenyl ring. DPV and SWV were used to generate peak current versus concentration curves for TAM. A linear response was obtained in the range comprised between 2x10(-6) and 4x10(-4) M for both techniques with detection limit of 3.34x10(-7) M for DPV and 2.45x10(-7) M for SWV. The methods were proposed for the determination of TAM in dosage forms adopting both DPV and SWV modes. The methods were extended to the in vitro determination of TAM in spiked serum samples.

A simple, sensitive, reproducible, and validated RP‐HPLC method with UV detection is described for the determination of deflazacort in raw material, pharmaceuticals, human serum samples, and in‐vitro drug dissolution studies. The separation was achieved using a C18 (250 × 4.6 mm; 5 µm) column and a mobile phase comprising acetonitrile, methanol, and 0.067 M KH2PO4 in the ratio (27:20:53, v/v/v), adjusted to pH 6.5 with 3 M NaOH. The results of analysis were treated statistically and it has been validated and proven to be rugged. The limit of detection and limit of quantification were found as 2.05 ng mL−1 and 6.83 ng mL−1 in mobile phase and 4.06 ng mL−1 and 13.55 ng mL−1 in human serum samples, respectively. The method produced linear response in the concentration ranges 10–30,000 ng mL−1 in mobile phase and 25–30,000 ng mL−1 in serum samples. The intra‐ and inter‐day assay precision of the method was within 0.92% relative standard deviations in mobile phase and 1.48% relative standard deviation...

A specific, sensitive, simple, and rapid HPLC method has been developed for the determination of valacyclovir (VACL) in raw material, pharmaceutical dosage forms, and human serum, in order to carry out drug dissolution studies from tablets. The chromatographic separation was achieved with acetonitrile:methanol:0.067 M KH2PO4 (27:20:53, v/v/v) adjusted to pH 6.5 with 3 M NaOH as mobile phase, a Waters Spherisorb C18 column, and UV detection at 244 nm. Etodolac was used as an internal standard. Linearity range was 5–20,000 ng mL−1. Limit of detection obtained was 0.38 and 0.14 ng mL−1 in mobile phase and spiked human serum samples, respectively. The described method can be readily applied, without any interferences from the excipients, for the determination of the drug in tablets, human serum samples, and drug dissolution studies. #Presented at 11th International Pharmaceutical Technology Symposium, September 9–11, 2002, Istanbul, Turkey.

A review of the principles and application of modern electroanalytical techniques, namely, cyclic voltammetry, linear sweep voltammetry, differential pulse voltammetry, differential pulse polarography, square wave voltammetry, square wave polarography, stripping voltammetric, and stripping polarographic techniques, is presented. The use and advantages of these techniques at different electrodes are discussed. The analytical applications of these techniques to pharmaceutical compounds in dosage forms and biological media are also discussed. Various selected studies on these subjects since 1995 are reviewed.

Simple, rapid, sensitive, and reproducible methods were developed for the assay of paroxetine in tablets. The electrooxidative behavior and determination of paroxetine on boron-doped diamond and edge plane graphite electrodes were investigated as details using cyclic, differential pulse, and square wave voltammetric methods. The oxidation process was irreversible and exhibited mixed diffusion-adsorption controlled process depending on pH. The dependence of the peak current and peak potentials on pH, nature of the buffer, and scan rate studies were examined as details. The linear responses have been obtained in the range from 7.0 × 10?7 M to 3.5 × 10?6 M with 6.95 × 10?9 M detection limit for the boron-doped diamond electrode and from 1.0 × 10?8 M to 5.0 × 10?6 M with 1.03 × 10?9 M detection limit for the edge plane graphite electrode. The possible electrooxidation mechanism of paroxetine was investigated by means of model compounds of tamsulosin and mebeverine. It can be suggested that alkoxybenzene moiety may be the responsible group for the oxidation of paroxetine (PRX). The developed methods have been successfully applied for the determination of paroxetine in pharmaceutical dosage form. © 2015, Springer-Verlag Berlin Heidelberg.

Three methods are presented for the simultaneous determination of lamivudine and zidovudine. The first method depends on first derivative UV spectrophotometry, with zero-crossing and peak-to-base measurement. The first derivative amplitudes at 265.6 and 271.6 nm were selected for the assay of lamivudine and zidovudine, respectively. The second method depends on first derivative of the ratio-spectra by measurements of the amplitudes at 239.5 and 245.3 nm for lamivudine and 225.1 and 251.5 nm for zidovudine. Calibration graphs were established for 1–50 μg/ml for lamivudine and 2–100 μg/ml for zidovudine. In the third method (HPLC), a reversed-phase column with a mobile phase of methanol:water:acetonitrile (70:20:10 (v/v/v)) at 0.9 ml/min flow rate was used to separate both compounds with a detection of 265.0 nm. Linearity was obtained in the concentration range of 0.025–50 μg/ml for lamivudine and 0.15–50 μg/ml for zidovudine. All of the proposed methods have been extensively validated. These methods allow a number of cost and time saving benefits. The described methods can be readily utilized for analysis of pharmaceutical formulations. There was no significant difference between the performance of all of the proposed methods regarding the mean values and standard deviations. The described HPLC method showed to be appropriate for simultaneous determination of lamivudine and zidovudine in human serum samples.

In the present study, a simple, sensitive, precise, and rapid HPLC method with UV detection for the analysis of lamivudine is developed and applied to the determination of anti HIV drug in commercial pharmaceutical dosage forms (tablets and oral solutions) and human serum. The gradient elution is performed with methanol:water (75 : 25, v/v) at a flow rate of 0.8 mLċmin−1, using a Spherisorb® C18 analytical column 150 × 4.6 mm, 5 µm. Deflazacort is used as internal standard. Absorbance is monitored at 265 nm. Total analysis time was ∼6 min. Data, with respect to precision and accuracy and limits of detection, are reported and discussed. The described method can be readily utilized for analysis of pharmaceutical products and pharmacokinetic studies as well.

Nefazodone, an antidepressant was electrochemically studied in various buffer systems and at different pH using glassy carbon electrode. Nefazodone was electrochemically oxidized at all pH values. According to the linear relation between the peak current and the nefazodone concentration differential pulse (DPV) and square wave (SWV) voltammetric methods for its quantitative determination in pharmaceuticals and human serum were developed. For analytical purposes, a very well resolved diffusion controlled voltammetric peak was obtained in 0.1 M H2SO4 at 0.99 and 1.03 V for DPV and SWV techniques, respectively. The linear response was obtained in the ranges of 8×10−7 to 6×10−4 M with a detection limit of 2.1×10−7 M for DPV and 1.17×10−7 M for SWV techniques. The repeatability and reproducibility of the methods were within 1.03, 0.81% relative standard deviations (R.S.D.) for peak currents and 0.40, 0.20% R.S.D. for peak potentials, for DPV and SWV, respectively. Precision and accuracy of the developed method was checked by recovery studies. The proposed methods were successfully applied to the individual tablet dosage form and human serum.

The O-methyl oxime grouping in the antibiotic cefepime is reduced in aqueous buffer solution at pH < 8 at a carbon electrode. The reduction of the protonated form of the oxime occurs in a single two-electron step. By comparison with anodic wave of 2-aminothiazole it was furthermore shown that the oxidation of cefepime involves the 2-amino group located on the thiazole ring in the side chain on C-7. Both reduction and oxidation peaks can be used for analytical purposes. © 2002 Elsevier Science B.V. All rights reserved.

Binary mixtures of l-dopa (LD) and benserazide (BEN) are analyzed by ratio spectra first derivative spectrophotometry. The procedures are accurate, non-destructive and do not require any separation step. This method depends on first derivative of the ratio spectra by division of the absorption spectrum of the binary mixture by a standard spectrum of one of the components and then calculating the first derivative of the ratio spectrum. The first derivative of the ratio amplitudes at 287.7 nm for LD and 251.4 nm for BEN was selected for the determination. Beer's law was obeyed in a range of concentration from 10 to 70 µg/ml for LD and from 5 to 50 µg/ml for BEN. The method was successfully applied for determining of two drugs in synthetic mixtures and in pharmaceutical preparations.

Ratio spectra of the first derivative spectrophotometric method for determination of melatonin (MEL) and pyridoxine HCl (PYR) in tablets in the presence of each other has been described. This technique depends on first derivative of the ratio spectra by division of the absorption spectrum of the binary mixture by a standard spectrum of one of the components and then calculating the first derivative of the ratio spectrum. The first derivative of the ratio amplitudes at 218.3 and 232.7 nm for MEL and 212.3, 282.6, and 304.6 nm for PYR were selected for the determination. The calibration graphs follow Beer's law in the ranges of 1–30 µg mL−1 for MEL and 1–22 µg mL−1 for PYR. The proposed method was successfully applied to the determination of these compounds in synthetic mixtures and in pharmaceutical preparations. The proposed method is simple, rapid and suitable for quality control applications.

A sensitive and selective electroanalytical method for the determination of tadalafil (TAD) using adsorptive stripping square wave voltammetry at multiwalled carbon nanotube paste electrode (MWCNTPE) and modified TiO2-multiwalled carbon nanotube paste electrode (TiO2-MWCNTPE) was presented. The calibration curves were linear in the concentration range of 3.6-8.1 and 12.7-61.1 mu M on MWCNTPE, 0.27-15.2 mu M on TiO2-MWCNTPE. The recommended method was successfully applied to the determination of the drug in tablets and human serum samples with good recoveries. The selectivity of the proposed method was considered in the presence of Ca2+, K+, Na+, 2-mercapto benzimidazole, thiourea, and dopamine by means of recovery tests. Interfering agents did not show considerable effect on TAD determination. No electroactive interferences from the tablet excipients and endogenous substances from biological material were detected. The possible electrooxidation pathway and the number of transferred electrons were also investigated.

In this work electrooxidation of cefadroxil monohydrate was investigated using a glassy carbon electrode depending on pH and supporting electrolyte. It was shown that the direct determination of the substance from capsules and in oral suspension could be made by differential pulse voltammetry (DPV). UV and first derivative UV spectrophotometric methods are also proposed as comparative methods.

In the present paper, rapid, sensitive, selective, accurate and precise analytical methodologies were developed for the determination of the antidepressant drug mirtazapine (MIR) using voltammetry and liquid chromatography. In cyclic voltammetry (CV), MIR showed one sharp oxidation peak and one additional wave in acidic media in the anodic direction; at pH 5.50, the mirtazapine peak was single and sharp. Under optimized conditions, the peak current showed a linear dependence with concentration in the range between 0.212 and 26.54 µg/mL for glassy carbon (GC) and 1.06 and 26.54 µg/mL for boron-doped diamond (BDD) electrodes using differential pulse (DP) and square wave (SW) voltammetric techniques. The possible oxidation mechanisms are also discussed. A simple and fully validated reverse phase-liquid chromatography (RP-LC) method to test for MIR in tablets was developed using an X-Select RP-18 column (250x4.60 mm ID x 5µm) at 25ºC with methanol:water (30:70, v/v, containing 15 mM o-phosphoric acid) as the mobile phase adjusted to pH 3.0. The RP-LC method allowed quantification over a MIR concentration range of 1.0-18.0 µg/mL. MIR was exposed to thermal, photolytic, or oxidative stress, as well as acid and base hydrolysis conditions, and the stressed samples were assayed by the proposed LC method. The proposed methods allow for a number of cost- and time-saving benefits.

Voltammetric, chromatographic, and spectrophotometric methods were developed for the simultaneous determination of bisoprolol fumarate (BIS) and hydrochlorothiazide (HCZ). Differential pulse and square wave voltammetry techniques were used to analyze BIS and HCZ simultaneously by measuring at about 1400 and 1100 mV, respectively. RP-HPLC was the second method for simultaneous analysis of the compounds. The mixture of BIS, HCZ, and moxifloxacin as an internal standard was separated on an RP Zorbax Eclipse XDB-C18 column (150 × 4.6 mm, id, 5 μm particle size) using acetonitrile–15 mM phosphate (25 + 75, v/v) mobile phase at a 1.0 mL/min flow rate. The third method was based on first derivative of the ratio-spectra method obtained from the measurements of the amplitudes at 246 and 257 nm for BIS and HCZ, respectively. All the proposed methods were effectively applied for the simultaneous determination of BIS and HCZ in tablet dosage forms without any time-consuming extraction, sample preparation, or derivatization procedures.

Deviations of the value of the rate constant for borate anions of the first step in the degradation of the antibiotic cefepime from Bronsted relation and deviations from i=f(pH) plots in voltammetric reductions of the oximino group led to investigation of the kinetics of degradation of cefepime in ammonia, borate, CHES and glycine buffers pH 9.3 using UV–visible spectra. Presence of at least two consecutive processes was detected and an interaction of cefepime with glycine has been proved. Identification of intermediates is under investigation.

Levodropropizine is a cough suppressant and easily oxidizable at the carbon-base electrodes. The electrooxidative behavior and determination of levodropropizine on glassy carbon and boron-doped diamond electrodes were investigated using cyclic, linear sweep, differential pulse, and square wave voltammetric methods. The dependence of the peak current and peak potentials on pH, concentration, nature of the buffer, and scan rate were examined. In this study, also simple and fully validated reverse phase-liquid chromatography (RP-LC) method for the assay of levodropropizine in syrup dosage form has been developed using X-Select RP-18 column (250x4.60 mm ID x ?5) at 25 °C with the mobile phase (containing 15 mM o-phosphoric acid) of acetonitrile:water (30:70, v/v) adjusted to pH 8.0. The proposed methods allow a number of cost and time saving benefits. Levodropropizine was also exposed to thermal, photolytic, oxidative stress, acid and base hydrolysis conditions, and the stressed samples were detected by the proposed LC method. The proposed methods were successfully applied for the determination of levodropropizine from pharmaceutical dosage forms. © 2013 Bentham Science Publishers.

The electrooxidative behavior and determination of lercanidipine (LRC) were investigated in aqueous acetonitrile medium at a boron-doped diamond electrode using voltammetric techniques. The LRC in selected supporting electrolyte presents a well-defined anodic response at 0.944 V, studied by the proposed method. The linear response was obtained in the ranges of 4 × 10−6 to 2 × 10−4 mmol L−1 range in 0.5 mmol L−1 sulfuric acid supporting electrolyte and 1 × 10−5 to 8 × 10−5 mmol L−1 range in spiked serum sample for square wave voltammetric technique. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage form and in the biological sample, respectively.

The electrochemical behavior of atorvastatin and amlodipine at a glassy carbon electrode has been studied using different voltammetric techniques. First derivative of the ratio voltammetric methods for determination of amlodipine and atorvastatin in tablets in the presence of the other compound has been described. This technique depends on the measuring of first derivative of the ratio voltammograms of each concentration as a function of the increased concentrations. DP and SW voltammetric methods depend on first derivative of the ratio-voltammetry by measurements of the selected potentials for amlodipine and atorvastatin. The linear response was within the range of 4×10−6–1×10−4 M for amlodipine and 2×10−6–1×10−4 M for atorvastatin. The proposed methods have been extensively validated.

A simple, reliable and selective differential pulse (DP) and square wave (SW) voltammetric methods at glassy carbon (GC) and boron-doped diamond (BDD) electrodes of lornoxicam in pharmaceutical dosage form and in spiked human serum samples have been developed and evaluated. The possible oxidation mechanism was discussed. The voltammetric study of the model compounds allowed elucidating the possible oxidation mechanism of lornoxicam. The dependence of the peak current and peak potentials on pH, concentration, nature of the buffer, and scan rate were investigated. The oxidation of lornoxicam gave a single and irreversible peak at both electrodes. The process was found diffusion controlled. For glassy carbon electrode, the linearity of the calibration curve was obtained in range of 4x10-7 M to 2x10-5 M for DPV method and 4x10-7 M to 4x10-5 M for SWV method in 0,1 M sulphuric acid solutions. Using boron-doped diamond electrode, the plot of the calibration curve was linear between 6x10-7 M and 1x10-4 M for both voltammetric methods in pH 2 BR buffer. The repeatability, reproducibility, precision and accuracy of the proposed methods were investigated.

The electrochemical oxidation of sertindole was investigated using cyclic, linear sweep voltammetry at a glassy carbon and boron-doped diamond electrodes. The aim of this study was to determine sertindole levels in serum and pharmaceutical formulations, by means of electrochemical methods. In cyclic voltammetry, depending on pH values, sertindole showed one or two irreversible oxidation responses. These two responses were found related to the different electroactive part of the molecule. Using second and sharp oxidation peak. two voltammetric methods were described for the determination of sertindole by differential pulse and square wave voltammetry at the glassy carbon and boron-doped diamond electrodes. Under optimized conditions. the current showed a linear dependence with concentration in the range between 1 x 10(-6) and 1 x 10(-4) M in acetate buffer at pH 3.5 and between 4 x 10(-6) and 1 x 10(-4) M in spiked human serum samples for both methods. The repeatability, reproducibility, selectivity, precision and accuracy of all the methods in all media were investigated and calculated. These methods were successfully applied for the analysis of sertindole pharmaceutical dosage forms and human serum samples. No electroactive interferences from the tablet excipients and endogenous substances from biological material were found. (C) 2008 Elsevier Ltd. All rights reserved.