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In this study, pKavalues of some ionizable butyrophenones, namely, benperidol, droperidol, and haloperidol were determined using by the dependence of the retention factor on pH of the mobile phase. The effect of the mobile phase composition on the ionization constant was studied by measuring the pKaat different methanol–water mixtures, ranging between 50 and 65% (v/v) using an LC-UV method. Additionally, a simple, accurate, precise, and fully validated analytical method for the simultaneous and individual determination of benperidol, droperidol, and haloperidol in their dosage forms was developed. Butyrophenones were exposed to thermal, photolytic, hydrolytic, and oxidative stress conditions, and the stressed samples were detected by the proposed method. [ABSTRACT FROM PUBLISHER]

A differential pulse (DP) and square wave (SW) voltammetric techniques were developed for the determination of irbesartan. The electrochemical behavior of irbesartan was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV) at the hanging mercury drop electrode (HMDE). Different parameters were tested to optimize the conditions of the determination. It was found that in the range of 8 × 10-6-1 × 10-4 M, the currents measured by both of methods presented a good linear property as a function of the concentration of irbesartan. In addition, validation parameters, such as reproducibility, sensitivity, and recovery were evaluated as well. The slope of the log Ip- log ν linear plot was 0.58 indicating the diffusion control for 0.5 M sulphuric acid without the need for separation or complex sample preparation, since there was no interference from the excipients and endogenous substances. The methods were successfully applied to the analysis of irbesartan in the pharmaceutical tablet formulations and in human serum samples. [ABSTRACT FROM AUTHOR]

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 × 10-4M 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 reproducibility of the methods for both media (supporting electrolyte and serum sample) were determined. Precision and accuracy of the developed method were used for the recovery studies. The standard addition method was used for the recovery studies. No electroactive interferences were found in biological fluids from the endogenous substances and additives present in tablets. [ABSTRACT FROM AUTHOR]

This work describes a new fully validated, simple, rapid, selective, and sensitive HPLC method with UV detection for the direct determination of abacavir in pharmaceutical dosage forms, raw materials, spiked human serum, and drug dissolution studies without any time-consuming extraction or evaporation steps prior to drug assay. The mobile phase employed was methanol: acetonitrile: 0.015 M KH2 PO4 (36:2.6:61.4 v/v/v) adjusted to pH 6.9 with 5N NaOH. The samples of 20μL were injected onto a Waters Spherisorh ODSI (250 × 4.6 mm, 5 μm particle size) column. Ketoprofen was used as internal standard. The flow rate was 1.0 mLmin-1. The retention times were 5.49 min for abacavir and 9.15 min for ketoprofen in mobile phase, 5.46 min for abacavir and 9.24 min for ketoprofen in serum samples. The samples were detected at 284 nm. The assay was linear in the concentration range 0.010-20μgmL-1 (r = 0.999) with a slope of 1.35 × 10-3: intercept of 0.0841 and the limit of detection was 0.00093 μg mL-1 in mobile phase and 0.025-20μg mL-1 (r = 0.999) with a slope of 1.44 × 10 -3 intercept of 0.0733 and the limit of detection was 0.00418μgmL-1 in human serum. The linearity of the detector response for abacavir was determined by plotting peak area ratios vs. concentration. It was successfully applied to the analysis of abacavir pharmaceutical preparations, and human serum samples without any interference by the recipients and endogenous substances. Moreover, the method can be used for the determination of abacavir for monitoring its concentration for in vitro dissolution studies. [ABSTRACT FROM AUTHOR]

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 absorbance and concentration values were used to predict the concentration of VST and HCT in their binary mixtures and tablets. The “Maple V” software was used for the numerical calculations. For this technique, mean recoveries and relative standard deviations were found as 101.2% and 1.58% for VST and 96.2% and 2.35% for HCT. Both techniques were successfully applied for the determination of these two drugs in tablets. [ABSTRACT FROM AUTHOR]

A high performance liquid chromatographic (HPLC) method is described for the determination of rofecoxib (RFC) in bulk drug, tablets, and human plasma samples. The methods are linear over the concentration ranges 0.005–30.0 and 0.010–10 µg mL−1 in mobile phase and human plasma, respectively. Chromatography was carried out on a reversed phase Spherisorb ODSI column using a mixture of acetonitrile:methanol: 0.067 M KH2PO4 (27:20:53, v/v/v) adjusted to pH 6.95 with 3 M NaOH. Detection was realized at 244 nm using a DAD detector. The retention time observed for RFC and etodolac (internal standard) at about 7.5 and 10.7 min, respectively. The proposed RP-HPLC method was validated for precision, accuracy, ruggedness, and recovery. The limit of detection was found to be 0.00143 and 0.00301 µg mL−1 in mobile phase and human plasma samples, respectively. The proposed method allows a number of cost and time saving benefits. The described method can be readily applied for the analysis of tablets, drug dissolution studies, and human plasma samples. This method could be used without any interference from tablet matrix and endogenous substance from the plasma samples. [ABSTRACT FROM AUTHOR]

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 deviations in human serum samples. This method was successfully applied for the determination of the drug in tablet dosage form, human serum, and drug dissolution studies. The results were found to be accurate, reproducible, and free from interference from the excipients or endogenous substance. #Presented at 3rd Agean Analytical Chemistry Days, September 29–October 3, 2002, Levos, Greece. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A novel, rapid, sensitive, accurate, and simple isocratic HPLC assay was developed to determine cerivastatin in pharmaceutical dosage forms and human serum. The proposed method was conducted using a reverse phase technique, UV monitoring at 232 nm, and losartan potassium as an internal standard. The detector response was linear in the range of 25–10000 ng/mL. This compound is well separated with a Waters C18 column (150 × 4.6 mm; 5μm particle size) by using a mobile phase consisting of a mixture of acetonitrile:0.01 M KH2PO4 adjusted to pH 3.1 with H3PO4 (35:65 v/v), at a flow rate of 1.0 mL/min. The limit of detection and the limit of quantitation of the procedure were 0.62 ng/mL and 2.07 ng/mL for cerivastatin, respectively. The retention time was 6.90 min for cerivastatin and 8.78 min for internal standard. No interferences were observed from tablet additives and the applicability of the method was examined by analyzing tablets containing cerivastatin. This method was also applied, without any interference from the excipients, for the determination of cerivastatin in drug dissolution studies. The proposed method was successfully applied to the analysis of cerivastatin in human serum. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A validated capillary electrophoretic method with UV detection is described for the determination of enoxacin [ENX] in pharmaceutical preparation and human serum. The experiments were carried out in a fused-silica capillary (ID=75 μm, total 88 cm, effective 58 cm length) using a 20 mM borate buffer at pH 8.6, applying a potential of 30 kV, 1 s of injection. Acetylpipedimic acid was used as an internal standard (IS) and the detection was performed at 265 nm. The tM±RSD% of ENX and IS were 4.8±0.9 and 5.5±1.2 minutes, respectively. A well-correlated calibration equation was obtained in the range of 3.1×10-6–3.1×10-5M ENX. Limit of detection (LOD) was 3.5×10-6 M (S/N = 3). A modified reversed-phase HPLC was also conducted using a C-18 ODS column for the analysis of ENX to compare to its applicability with the CE method. An isocratic elution was performed using a mobile phase of 10 mM phosphate buffer (pH 4.0) and acetonitrile (85:15;v/v) detecting at 260 nm. The determination of ENX in the pharmaceutical tablet formulation was carried out by both methods and the results of a single tablet (as mg with their RSD% values) was found to be 421.4±1.0 and 415.9±0.9 by CE and HPLC, respectively. ENX analysis was also performed by a standard addition method in serum, and the recoveries were found to be 89.7±0.6 (CE) and 78.8±4.9 (HPLC). It was concluded that capillary electrophoresis for the determination of ENX is a promising method for routine analysis and pharmacokinetic and bioavailability studies. [ABSTRACT FROM AUTHOR]

A new, simple, precise, rapid, and accurate RP-HPLC method has been developed for the simultaneous determination of losartan potassium and hydrochlorothiazide from tablets and human serum. Chromatography was carried out on a C18 reversed-phase column using a mixture of 0.01 M KH2PO4: acetonitrile (65:35; v/v) adjusted to pH 3.1 with H3PO4 at a flow rate 1.0 mL/min. Detection was realised at 232 nm using a UV detector. Linearity was obtained in the concentration range of 25–10000 ng/mL and 50–10000 ng/mL for losartan potassium and hydrochlorothiazide, respectively. The limit of detection and the limit of quantification of the procedure were found to be 1.02 ng/mL and 3.39 ng/mL for losartan potassium; 4.49 ng/mL and 14.96 ng/mL for hydrochlorothiazide, respectively. This method was succesfully applied without any interferences to the simultaneous analysis of losartan potassium and hydrochlorothiazide in human serum and pharmaceutical dosage forms in the presence of each other. [ABSTRACT FROM AUTHOR]

A new, simple, precise, accurate, and rapid reverse-phase high performance liquid chromatographic (RP-HPLC) method has been developed for the simultaneous determination of fosinopril sodium and hydrochlorothiazide from tablets. The procedure is based on the use of the RP-HPLC method with a UV detector. Each analysis requires no longer than 6 minutes. A reversed phase C18 column with a mobile phase composed of a mixture of methanol: water (40:60, v/v), adjusted to pH 4 with 10% orthophosphoric acid, was used to separate both compounds with sulfamethoxazole, as an internal standard, in a reasonable time period. The linearity range for fosinopril sodium and hydrochlorothiazide was 1.6–30 μg/mL and 1–30 μg/mL, respectively. The detection limits for fosinopril sodium and hydrochlorothiazide were 0.29 μg/mL and 0.26 μg/mL, respectively. [ABSTRACT FROM AUTHOR]

A simple, reliable, and rapid RP-HPLC method has been developed for the determination of clenbuterol HCl in human serum and pharmaceuticals, in order to carry out drug dissolution studies for clenbuterol tablets. This compound is well separated on a C18 column by using the mobile phase consisting of a mixture of acetonitrile and ion-pair buffer (32:68; v/v) at a flow rate of 1.5 mL/min. Detection was carried out using a UV detector at 244 nm. ephedrine HCl was used as an internal standard. Minimum detection limit obtained was 3.78 ng/mL. This method was applied, without any interferences from the excipients, for the determination of the drug in tablet formulation, human serum, and drug dissolution studies. [ABSTRACT FROM AUTHOR]

A sensitive and simple high performance liquid chromatographic method for the assay of fluoxetine HCl was developed. The procedure is based on the use of the reversed-phase high performance liquid chromatographic method with UV detector. Each analysis required no longer than 6 minutes. The detector response was linear in the range of 0.01–50 μg/mL for fluoxetine HCl. The detection limit was found to be 0.0057 μg/mL. There was no significant difference between interday and intraday studies for fluoxetine HCl determined for two different concentrations. This method was applied, without any interferences from the excipients, for the determination of the drug in capsules and in drug dissolution studies. This method can be useful in routine quality control analysis of fluoxetine HCl pharmaceutical dosage form. [ABSTRACT FROM AUTHOR]