Adsorptive stripping voltammetric determination of cefetamet in human urine

On the basis of previously established mechanism of cefetamet (CEF) reduction, two methods were suggested for CEF determination-differential pulse polarographic and differential pulse adsorptive stripping voltammetric method. Two pH values were chosen, 2.0 and 8.4, where the electrochemical process was defined as one four-electron and two two-electron processes, respectively. The methods were performed in Britton-Robinson (BR) buffer and the corresponding calibration graphs were constructed and statistical parameters were evaluated. Applying the AdSV method at pH 2.0 linearity was achieved from 2 x 10(-8) to 2 x 10(-7) M with limit detection and limit determination of 4 x 10(-9) and 1.4 x 10(-8) M, respectively. At pH 8.4, the linearity was obtained between 6 x 10(-8) and 6 x 10(-7) M, with limit detection and limit determination of 1.5 x 10(-8) and 5 x 10(-8) M, respectively. Since the AdSV method enabled lower concentrations of CEF to be determined, this method was tested for CEF determination in spiked urine samples, and DPP method was used as a comparative one.     

Voltammetric and HPLC determination of dorzolamide hydrochloride in eye drops

The behaviour of dorzolamide hydrochloride (DOR) was investigated at a glassy carbon electrode in different buffer systems using cyclic (CV), linear sweep (LSV) and differential pulse voltammetry (DPV). The oxidation process was found to be irreversible over the pH range studied (2.0-8.0) and was shown to be diffusion controlled. An analytical method with adequate precision and accuracy was developed for the determination of DOR in Britton-Robinson buffer (BRb) at pH = 3.06 containing 10% methanol as supporting electrolyte. The peak current varied linearly with DOR concentration in the range 4.0 x 10(-5)-6.0 x 10(-4) M. Furthermore, a HPLC method with diode array detection was developed. A calibration graph was established for 1.1 x 10(-6)-1.9 x 10(-4) M of DOR. The procedures were successfully applied for the determination of the drug in eye drops.     

"Determination of domperidone in tablet dosage form by anodic differential pulse voltammetry"

A differential pulse voltammetric method was described for the determination of domperidone. The method was based on the anodic oxidation of domperidone on a glassy carbon electrode at +0.64 V vs. SCE in Britton-Robinson buffer solution of pH 2.3. The reversibility of the oxidation was tested by cyclic voltammetry; the electrode process is irreversible and diffusion-adsorption controlled. Calibrations are linear over the range 1.0 x 10(-6)-2.0 x 10(-5) M of domperidone with a detection limit of 4.0 x 10(-7) M. The method was applied, without any interference from the excipients, to the determination of the drug in a tablet dosage form.     

Determination of pantoprazole by adsorptive stripping voltammetry at carbon paste electrode

A voltammetric method was described for the determination of pantoprazole by differential-pulse adsorptive stripping voltammetry at a carbon paste electrode. Accumulation of pantoprazole was found to be optimized in Britton-Robinson buffer (0.04 M, pH 4.0) solution following 5 min accumulation time at open circuit condition. Under optimized conditions, the current showed a linear dependence with concentration in the range 1.0 x 10(-7)-1.0 x 10(-5) M. The detection limit was 2.0 x 10(-8) M. The method was applied successfully for the analysis of pantoprazole in tablet dosage form. The results of accuracy and precision were comparable to those obtained by spectrophotometry.     

Electrooxidation of cetirizine dihydrochloride with a glassy carbon electrode

The electrochemical oxidation of cetirizine dihydrochloride (CTZH) at different pHs and concentrations using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with a glassy carbon (GC) electrode was studied. This study indicated that CTZH was susceptible to oxidation. The statistical analysis proved that the CV and DPV methods were reproducible and selective for the determination of CTZH. The results showed that voltammetric determination of CTZH could be made in the concentration ranges of 2 x 10(-5) M - 1 x 10(-4) M by CV and 2 x 10(-5) M - 1 x 10(-4) M by DPV with a GC electrode. The oxidation process was found to be irreversible over the pH range studied (2-10) and was shown to be mainly diffusion controlled. The determination of CTZH was performed in phosphate buffers covering the pH range of 2-10. No satisfactory results were obtained in 0.5 M H2SO4 solution. With both of the methods used the best results were obtained in phosphate buffer of pH 8. Application of the suggested methods to pharmaceutical formulations is presented and compared with the first derivative spectrophotometric method. No interference was observed from common pharmaceutical adjuvants.     

Voltammetric and spectrophotometric techniques for the determination of the antihypertensive drug Prazosin in urine and formulations

A sensitive method was developed to determine Prazosin using a nafion modified carbon paste electrode (NMCPE). Prazosin was accumulated at a potential of 750 mV in Britton-Robinson buffer (pH 6.0) and then a negative sweep was made obtaining a cathodic peak close to 0 V. Cyclic voltammetric studies indicated that the process was quasi-reversible, and fundamentally controlled by adsorption. To obtain a good sensitivity, the instrumental and accumulation variables were studied using differential pulse voltammetry (DPV). Adsorptive voltammetric peak currents showed a linear response for Prazosin concentrations in the range between 4.0 x 10(-11) and 4.0 x 10(-8) M with two different slopes, and a detection limit (LOD) of 3.1 x 10(-11)M was obtained. The variation coefficient (CV) for a 8.0 x 10(-10) M solution (n = 10) was 4.08%. A spectrophotometric study of Prazosin was also carried out and two absorption bands were obtained at 246 and 329 nm (pH 1.8). The band at 329 nm was pH-dependent and its height and position changed with the pH values, so this allowed the pK'a determination (7.14 +/- 0.20) using different methods. The detection limit reached by means of UV-spectrophotometry was 0.9 x 10(-7) M, and the variation coefficient for 1.5 x 10(-5) M Prazosin solutions was 1.14% (n = 10). Although the sensitivity of the UV-spectrophotometric method was lower than that obtained using adsorptive stripping-differential pulse voltammetry (AdS-DPV), it could be applied to the determination of Prazosin in Minipres tablets. The voltammetric method was used for the determination of the drug in human urine samples at trace levels with good recoveries.     

Determination of atovaquone in tablets by differential pulse polarography

A differential pulse polarographic method is presented for the determination of atovaquone in its pharmaceutical formulations. The polarographic behaviour of atovaquone was examined in various buffer systems over the pH range 3.0-10.0. In Britton Robinson buffer/methanol solution (1:1; v/v; pH 8.5) the differential pulse polarograms exhibited reproducible peaks at Ep--0.43 V vs. silver/silver chloride/potassium chloride (3M). Under these conditions, strict linearity between atovaquone concentration and peak height was observed in the 2.7 x 10(-6)-3.5 x 10(-5) M concentration range. The detection limit was calculated to be 0.41 microgram/ml. The polarographic method was applied to the determination of the content of atovaquone in various pharmaceutical preparations. For the polarographic analysis of atovaquone in Wellvone and Malarone tablets no separation step was necessary. In order to evaluate the concentration of atovaquone, the standard addition method was applied. The analysis of Wellvone tablets led to a mean value of 250.4 mg with a relative standard deviation (Srel) of +/- 2.1% and of Malarone tablets 252.3 mg with a Srel of +/- 2.4%.     

Electrochemical study of imipenem's primary metabolite at the mercury electrode. Voltammetric determination in urine

Imipenem shows a fast chemical conversion to the more stable imin form (identical to that from biochemical dehydropeptidase degradation) in aqueous solutions that shows a wave at lower cathodic potential than the imipenem one. The aim of this work is the study of the electrochemical behaviour of the primary metabolite of imipenem (M1) and the proposal of electrochemical methods for the determination of M1 in human urine samples. Electrochemical studies were realized in phosphate buffer solutions over pH range 2.0-8.0 using differential pulse polarography, dc-tast polarography, cyclic voltammetry and linear sweep voltammetry (staircase). In acidic media, a non-reversible diffusion-controlled reduction involving two electrons and two protons occurs and the mechanism for the reduction was suggested. A differential pulse polarographic method for the determination of M1 in the concentration range 10(-6) to 10(-4)M with a detection limit of 4.5 x 10(-7)M was proposed. Also, a method based on controlled adsorptive pre-concentration of M1 on the hanging mercury drop electrode (HMDE) followed by linear sweep voltammetry allows its determination in the concentration range 2 x 10(-9) to 4 x 10(-8)M with a detection limit of 1.05 x 10(-9)M. The proposed methods have been used for the direct determination of M1 in spiked human urine and real human-derived urine with good results and should be appropriate for monitoring purposes.     

Electrochemical study of natamycin--analytical application to pharmaceutical dosage forms by differential pulse voltammetry

The electrochemical oxidation and determination of natamycin has been carried out at a carbon paste electrode in aqueous solutions in the pH range of 2.5-10.30 by cyclic and differential pulse voltammetry. Best results were obtained with the differential pulse voltammetric technique in 0.5 M sulfuric acid at pH 1.82. The diffusion controlled nature of the waves was established. A differential pulse voltammetric technique for the determination of natamycin 0.5 M sulfuric acid which allows quantitation over the range of 2 x 10(-6)-8 x 10(-5) M range method is proposed. Limit of detection and limit of quantitatification were 1.5 x 10(-6) and 5 x 10(-6) M, respectively. Based on this study a simple, rapid, selective and sensitive voltammetric method was developed for the determination of natamycin in capsules. In order to validate the proposed method, UV spectroscopy was applied.     

Anodic voltammetric assay of lansoprazole and omeprazole on a carbon paste electrode

The electrochemical oxidations of lansoprazole and omeprazole have been studied at a carbon paste electrode by cyclic and differential-pulse voltammetry in Britton-Robinson buffer solutions (0.04 M; pH 6.0-10.0). The drug produced a single oxidation step. By differential-pulse voltammetry, a linear response was obtained in B-R buffer pH 6.0 in a concentration range from 2.0 x 10(-7) to 5.0 x 10(-5) M for lansoprazole or omeprazole. The detection limits were 1.0 x 10(-8) and 2.5 x 10(-8) M for lansoprazole and omeprazole, respectively. The method was successfully applied for the analysis of omeprazole and lansoprazole in capsules. The results were comparable to those obtained by spectrophotometry.     

Simultaneous determination of melatonin and pyridoxine in tablet formulations by differential pulse voltammetry.

A method has been developed for the simultaneous determination of melatonin (MT) and pyridoxine hydrochloride (PY) in pharmaceutical dosage forms by differential pulse voltammetry, based on the oxidation of both drugs at a glassy carbon electrode. Cyclic and linear scan voltammetry were used to examine the influence of pH, nature of the buffer, scan rate and concentration. The results in 0.5 M H2SO4 with 20% methanol allowed a method to be developed for the determination of MT and PY simultaneously and in the presence of each other in the ranges 2 x 10(-5)-8 x 10(-5) and 2 x 10(-5)-4 x 10(-4) M, with the detection limits of 5.86 x 10(-6) and 2.45 x 10(-6) M, respectively. The proposed method was successfully applied to the commercial tablets containing this drug combination without any interference by the excipients.     

Electroanalytical characteristics of piribedil and its differential pulse and square wave voltammetric determination in pharmaceuticals and human serum

The electrochemical oxidative behavior of piribedil (PR) was described. It was investigated by cyclic, linear sweep, differential pulse (DPV) and square wave (SWV) voltammetric techniques. The redox behavior of PR was found irreversible. Different parameters were tested to optimize the conditions for the determination of PR. The dependence of intensities of currents and potential on pH, concentration, scan rate, nature of the buffer was investigated. Two sensitive methods for the measurement of PR were described. For analytical purposes, a very well resolved diffusion controlled voltammetric peak was obtained in 0.1 M H(2)SO(4) and pH 5.7 acetate buffer. The determination peaks are obtained at 1.27 and 0.95 V for differential pulse and 1.29 and 0.97 V for SWV in 0.1 M H(2)SO(4) and pH 5.7 acetate buffer, respectively. The linear response was obtained in the ranges of 2 x 10(-6)-1 x 10(-3) M in 0.1 M H(2)SO(4) and 2 x 10(-6)-8 x 10(-4) M in pH 5.7 acetate buffer for both techniques. The proposed techniques were successfully applied to the determination of PR in tablet dosage forms and human serum. Excipients did not interfere in the determination. The necessary statistical validation reveals that the proposed methods are free from significant systematic errors.     

Determination of 5-aminosalicylic acid in pharmaceutical formulation by differential pulse voltammetry

The oxidative behaviour of 5-aminosalicylic acid (5-ASA) has been investigated by differential pulse voltammetry using a glassy carbon electrode in different buffer systems. Linear sweep voltammetry was used to study the influence of pH on the peak current and peak potential. The solution conditions and instrumental parameters were optimized to obtain a good sensitivity. The Britton-Robinson buffer of pH 1.81 was selected as a suitable analytical medium in which 5-ASA exhibited a sensitive diffusion controlled oxidative peak at 0.564 V (vs. Ag/AgCl). The peak current varied linearly with drug concentration in the range between 1 x 10(-4) and 2 x 10(-6) M. The proposed voltammetric method has been applied to the determination of the drug in commercial delayed-release tablet forms. A mean recovery of 101.23% with a relative standard deviation of 1.35% was obtained.     

Voltammetric investigation of oxidation of zuclopenthixol and application to its determination in dosage forms and in drug dissolution studies

The oxidative voltammetric behaviour of zuclopenthixol (ZPT) at a glassy carbon has been studied using cyclic, linear sweep and differential pulse voltammetry. Oxidation of the drug produced three pH dependent anodic steps (representing an irreversible oxidation). Using differential pulse voltammetry, the drug yielded a well-defined voltammetric response in phosphate buffer, pH 5.2 at + 0.82 V (vs. Ag/AgCl). This process could be used to determine ZPT concentrations in the range 8 x 10(-7)-2 x 10(-4) M. The method was applied, without any interferences from the excipients, to the determination of the drug in tablets and oral drops, and in drug dissolution studies.     

Electrochemical methods for determination of the protease inhibitor indinavir sulfate in pharmaceuticals and human serum

Indinavir sulfate is an inhibitor of the human immunodeficiency virus (HIV) protease. The aim of this study was to determine indinavir levels in serum and pharmaceuticals, by means of electrochemical methods using the hanging mercury drop electrode (HMDE). Indinavir exhibited irreversible cathodic waves over the pH range 2.00-12.00 in different supporting electrolytes. The current-concentration plot was rectilinear over the range from 8 x 10(-7) M to 8 x 10(-6) M with a correlation coefficient of 0.996 for differential pulse voltammetry (DPV) and 8 x 10(-7) M to 1 x 10(-5) M with correlation of 0.999 M for osteryoung square ware voltammetry (OSWV) in Britton-Robinson buffer at pH 10.00. The wave was characterized as being irreversible and diffusion-controlled. The proposed methods were fully validated and successfully applied to the determination of indinavir in capsules and spiked human serum samples with good recoveries. The repeatability and reproducibility of the methods as well as precision and accuracy (such as supporting electrolyte, serum samples) were determined. No electroactive interferences from the endogenous substances were found in serum samples.     

Voltammetric assay of the anthelmintic veterinary drug nitroxynil in bulk form and formulation at a mercury electrode

The electrochemical behavior of the anthelmintic veterinary drug nitroxynil at the mercury electrode was studied in a series of Britton-Robinson universal buffer of pH 1.9-11 containing 20% (v/v) ethanol using dc-polarography cyclic voltammetry and controlled-potential coulometry. The voltammograms exhibited two irreversible cathodic steps over the pH range 1.9-10.2; the height of the first step is double that of the second one. Controlled-potential coulometry in the B-R universal buffer of pH 1.9-10 at a mercury pool working electrode revealed the consumption of four and two electrons via the first and second reduction steps, respectively, which attributed to reduction of the NO2 group to the hydroxylamine stage (first step), and then to the amine stage (second step). Three voltammetric analytical procedures including dc-polarography, differential-pulse adsorptive stripping voltammetry and square-wave adsorptive stripping voltammetry were optimized for the direct determination of bulk nitroxynil. The three proposed procedures were applied for analysis of bulk nitroxynil with limits of detection of 3 x 10(-5), 1.31 x 10(-8) and 8.4 x 10(-10)M and limits of quantification of 1 x 10(-5), 4.36 x 10(-8) and 2.80 x 10(-9)M, respectively. The three procedures were successfully applied to the determination of nitroxynil in formulation (Dovenix, 25% nitroxynil injection solution) without the necessity for sample pretreatment and/or time-consuming extraction steps prior to the analysis.     

Utility of an oxidation reaction for the spectrophotometric determination of acarbose in controlled release tablets at various simulated gastrointestinal media

A sensitive kinetic method for spectrophotometric determination of acarbose is developed and validated for the determination of the drug in bulk and pharmaceutical formulations. The drug was estimated in simulated gastrointestinal media i.e., 0.1 M HCl (pH 1.2) and phosphate buffer (pH 6.8). The method involves the oxidation of acarbose by treating it with a strong oxidizing agent (potassium permanganate (1 x 10(-2) M)) in alkaline media. The reaction kinetics was determined for 20 min at room temperature. The reaction followed first order kinetics and the absorbance of the corresponding manganate ions produced was determined at 610 nm. The absorbance-concentration plot was found to be rectilinear over the concentration range of 2-20 microg/mL. The proposed method was used for estimation of the drug in a novel controlled release dosage form. Thus, the method developed was simple, reproducible and can be successfully applied for the determination of the drug in simulated gastrointestinal fluid.     

Determination of olsalazine sodium in pharmaceuticals by differential pulse voltammetry

The electrochemical oxidation of olsalazine sodium was investigated by cyclic, linear sweep, differential pulse and square wave voltammetry using glassy carbon disc electrode in different buffer systems. Best results were obtained for the determination of olsalazine using the differential pulse voltammetric technique in phosphate buffer at pH 7.0. The electroactive species exhibits a diffusion-controlled voltammetric wave and its differential pulse peak current shows a linear dependence on olsalazine concentration in the range between 2 x 10(-6) M and 2 x 10(-4) M. This relationship has been applied to the determination of olsalazine in commercial capsule dosage forms. The recovery study shows good accuracy and precision for the assay developed. A UV spectrophotometric assay is also reported for comparison.     

Polarographic determination of propranolol in pharmaceutical formulation

Propranolol was reacted with nitric acid to give nitropropranolol and was then measured in Britton-Robinson solutions in the pH range 2.0-12.0 by differential-pulse polarography. Nitropropranolol gave rise to a well-resolved differential-pulse polarographic peak at pH 2.0. A linear calibration graph in the range 5.0 x 10(-7)-5.0 x 10(-5) M and a detection limit of 5 nM was obtained. The relative standard deviation was 1.95% (n = 10) at 5 x 10(-6) M. The effect of common exceipient on the peak height was evaluated. The method was applied for the determination of the drug in the tablet dosage form.     

FIA of sildenafil citrate using UV-detection

A flow injection analysis (FIA) of sildenafil citrate (SLD) using UV detection is described in this study. The best solvent system was found to be consisting of 0.2 M phosphate buffer at pH 8 having 10% MeOH. A flow rate of 1 ml. min(-1) was pumped and active material was detected at 292 nm. The calibration equation was linear in the range of 1x10(-6)-5x10(-6) M. Limit of detection (LOD) and limit of quantitation (LOQ) were calculated to be 3x10(-7) and 8.9x10(-7) M with a R.S.D. 1.9 and 0.6% (n=7), respectively. The proposed method was applied to the determination of SLD in VIAGRA tablet, containing 50 mg active material. The results were compared with those obtained from UV-Spectrophotometry. The results showed that there is a good agreement between FIA method and the UV-Spectrophotometry. The validation studies were realised by the related applications and the results were evaluated statistically. According to the results, insignificant difference was observed between the methods.