Spectrofluorometric determination of verapamil hydrochloride in pharmaceutical preparations and human plasma using organized media: application to stability studies

A highly sensitive spectrofluorometric method was developed for the determination of verapamil hydrochloride (VP HCl) in pharmaceutical formulations and biological fluids. The proposed method is based on investigation of the fluorescence spectral behavior of VP HCl in micellar systems, such as sodium dodecyl sulfate (SDS) and beta-cyclodextrin (beta-CD). In aqueous solutions of borate buffer of pH 9 and 8.5, VP HCI was well incorporated into SDS and beta-CD, respectively, with enhancement of its native fluorescence. The fluorescence was measured at 318 nm after excitation at 231 nm. The fluorescence intensity enhancements were 183 and 107% in SDS and in beta-CD, respectively. The fluorescence-concentration plots were rectilinear over the range of 0.02-0.2 and 0.02-0.25 microg/mL, with lower detection limits of 5.58 x 10(-3) and 3.62 x 10(-3) microg/mL in SDS and beta-CD, respectively. The method was successfully applied to the analysis of commercial tablets and the results were in good agreement with those obtained with the official method. The method was further applied to the determination of VP HCl in real and spiked human plasma. The mean % recoveries in the case of spiked human plasma (n=4) was 92.59 +/- 3.11 and 88.35 +/- 2.55 using SDS and beta-CD, respectively, while that in real human plasma (n=3) was 90.17 +/- 6.93 and 89.17 +/- 6.50 using SDS and beta-CD, respectively. The application of the method was extended to the stability studies of VP HCl after exposure to ultraviolet radiation and upon oxidation with hydrogen peroxide.     

Effect of organized media on the chromatographic and electrophoretic determination of pharmaceutical preparations in biological samples

Procedures were developed for the simultaneous determination of endogenous and exogenous steroids in biological fluids by reversed-phase high-performance liquid chromatography (RP HPLC), capillary zone electrophoresis, and micellar electrokinetic chromatography (MEKC) using components of organized media (micelles of sodium dodecyl sulfate, β-cyclodextrin, sulfo-β-cyclodextrin, and carbamide). The detection limits were 50 and 500 ng/mL without preconcentration and 3–5 and 5–10 ng/mL with preconcentration for RP HPLC and MEKC, respectively. The time of separation was 30 and 10 min, and the total time of analysis (including preconcentration and the conditioning of a column or a capillary) was 80 and 90 min for RP HPLC and MEKC, respectively.     

Spectrofluorometric determination of fluvoxamine in dosage forms, spiked plasma, and real human plasma by derivatization with fluorescamine

A sensitive, simple, and selective spectrofluorometric method was developed for the determination of fluvoxamine (FXM) in pharmaceutical formulations and biological fluids. The method is based upon the reaction between the drug and fluorescamine in borate buffer of pH 8.0 to yield a highly fluorescent derivative that is measured at 481 nm after excitation at 383 nm. The different experimental parameters affecting the development and stability of the reaction product were carefully studied and optimized. The method was applied for the determination of the drug over the concentration range of 0.1-1.1 microg/mL with a detection limit of 0.01 microg/mL (2 x 10(-8) M). The proposed method was successfully applied to the analysis of commercial tablets. The results obtained were in good agreement with those obtained using a reported spectrophotometric method. The method was applied for the determination of FXM in spiked human plasma with recovery (n=4) of 97.32 +/- 1.23%, while that in real human plasma (n=3) was 90.79 +/- 2.73%. A proposal for the reaction pathway is presented.     

Spectrofluorometric determination of nicardipine,nifedipine and isradipine in pharmaceutical preparations and biological fluids

A simple and highly sensitive spectrofluorometric method was developed for the determination of some 1,4-dihydropyridine compounds namely, nicardipine, nifedipine and isradipine in pharmaceutical preparations and biological fluids. The method is based on the reduction of nicardipine, nifedipine and isradipine with Zn/HCl and measuring the fluorescence intensity obtained (λ_em/λ_ex) at 460/364, 450/393 and 446/360 nm, respectively. The factors affecting the development of the fluorophore and its stability were studied and optimized. The effect of some surfactants such as β-cyclodextrin (βCD), carboxymethylcelullose (CMC), sodium dodecyl sulphate (SDS) and triton X-100, on the fluorescence intensity was studied. The fluorescence intensity-concentration plots of nicardipine, nifedipine and isradipine were rectilinear over the ranges 0.4–6.0, 0.2–4.0 and 0.1–9.0 μg ml⁻¹ with detection limits of 0.0028, 0.017 and 0.016 μg ml⁻¹, respectively. The proposed method was successfully applied to commercial tablets containing the compounds; the percentage recovery agreed well with those obtained using the official methods. The method was further extended to the in vitro determination of the compounds in spiked human plasma and urine samples. A proposal of the reduction reaction pathway was postulated.      

Polarographic determination of mitoxantrone in pharmaceutical preparations and biological media

An A.c. tast polarographic method for the determination of mitoxantrone in pharmaceutical preparations and biological media is described. The optimum pH for the extraction of the drug from various samples into a 4:1 mixture of chloroform-isopropanol is indicated. The effect of other parameters such as temperature, composition of supporting electrolyte and polarographic variables (drop time, a.c. voltage amplitude, voltage sweep rate) on the sensitivity and reproducibility of the method is also verified, and a simple and precise recommended method is proposed for the determination of mitoxantrone. The method is found to be applicable to the analysis of the drug in extracted phases at concentrations 5 x 10(-7) - 2.5 x 10(-5) M with a precision of about 1.5% (relative standard deviation). The limit of detection is calculated as 3.5 x 10(-7) M for both aqueous pharmaceutical preparations and biological media.     

Spectrofluorometric determination of ketorolac tromethamine via its oxidation with cerium(IV) in pharmaceutical preparations and biological fluids

A simple and sensitive fluorometric method for determination of ketorolac tromethamine was studied. The method depends on oxidation of the drug with cerium(IV) and subsequent monitoring of the fluorescence of the induced cerium(III) at lambda(em) 365 nm after excitation at 255 nm. Different variables affecting the reaction conditions, such as the concentrations of cerium(IV), sulfuric acid concentration, reaction time, and temperature, were carefully studied and optimized. Under the optimum conditions, a linear relationship was found between the relative fluorescence intensity and the concentration of the investigated drug in the range of 0.1-0.8 microg/mL. No interferences could be observed from the excipients commonly present in dosage forms. The proposed method was successfully applied to the analysis of the investigated drug in its pure form, pharmaceutical preparations, and biological fluids with good accuracy and precision. The recoveries for pharmaceutical formulations ranged from 99.8-101.0 +/- 0.6% for tablets, 98.5-101.0 +/- 1.0% for ampoules, and 99.0-100.5 +/- 0.7% for eye drops. The results obtained by the proposed method were satisfactory compared with those obtained by the official method. The recoveries for biological fluids were 99.1-100.4 +/- 0.7 and 99.0-100.0 +/- 0.5% for plasma and urine, respectively.     

Rapid and accurate amperometric determination of acetaminophen in pharmaceutical preparations and spiked human blood serum samples at cadmium pentacyanonitrosylferrate modified glassy carbon electrode

The present work describes a rapid and accurate amperometric technique for the determination of acetaminophen (ACT) in pharmaceutical preparations and human blood serum, based on electrocatalytic oxidation of ACT at a glassy carbon electrode modified by cadmium pentacyanonitrosylferrate (CdPCNF) film. The electrocatalytic response of the modified GC electrode was linear over the concentration of 1.64-52.90 μM. The limit of detection was found to be 2.04 μM by amperometric technique. The method was successfully utilized for the determination of ACT in various pharmaceutical preparations and the results have been statistically compared with those obtained by the official method. The interference of some pharmaceutical and biological compounds was investigated. The results of interference study showed that the Nafion-coated CdPCNF|GC electrode can be utilized as a selective amperometric sensor for acetaminophen determination in human blood serum. The mean value of rate constant k for catalytic reaction, and the diffusion coefficient of ACT (D) in the phosphate buffer solution of pH 7.2 were found to be 4.27 × 10² M?¹ s?¹, and (4.25 ± 0.33) × 10^?6 cm² s^?1, respectively.     

Determination of bupropion using liquid chromatography with fluorescence detection in pharmaceutical preparations, human plasma and human urine

A novel pre-column derivatization reversed-phase high-performance liquid chromatography with fluorescence detection is described for the determination of bupropion in pharmaceutical preparation, human plasma and human urine using mexiletine as internal standard. The proposed method is based on the reaction of 4-chloro-7-nitrobenzofurazan (NBD-Cl) with bupropion to produce a fluorescent derivative. The derivative formed is monitored on a C18 (150 mm × 4.6 mm i.d., 5 μm) column using a mobile phase consisting of methanol-water 75:25 (v/v), at a flow-rate of 1.2 mL/min and detected fluorimetrically at λ(ex) = 458 and λ(em) = 533 nm. The assay was linear over the concentration ranges of 5-500 and 10-500 ng/mL for plasma and urine, respectively. The limits of detection and quantification were calculated to be 0.24 and 0.72 ng/mL for plasma and urine, respectively (inter-day results). The recoveries obtained for plasma and urine were 97.12% ± 0.45 and 96.00% ± 0.45, respectively. The method presents good performance in terms of precision, accuracy, specificity, linearity, detection and quantification limits and robustness. The proposed method is applied to determine bupropion in commercially available tablets. The results were compared with an ultraviolet spectrophotometry method using t- and F-tests.     

Analytical determination of nimesulide and ofloxacin in pharmaceutical preparations using square-wave voltammetry

The electrochemical behaviour and analytical detection procedure for nimesulide (NIM) and ofloxacin (OFX) and their assay in commercial formulations were evaluated using square-wave voltammetry (SWV) combined with a hanging mercury drop electrode (HMDE). All experimental and voltammetric conditions were previously optimized to obtain the best analytical signal in terms of intensities and profile of the reduction peaks. For NIM, the peak currents were related to the one-electron reduction of a nitro group to a stable radical anion, which is followed by a one-electron transfer and a protonation step with a consequent formation of a nitrosoanion. The voltammetric results indicated that the mechanism of OFX involved the transfer of two electrons and two protons in a totally irreversible reduction related to the conversion of a ketone group to an alcohol group. Analytical parameters such as linearity range, equations of the analytical curves, correlation coefficients, detection and quantification limits, recovery efficiency, and relative standard deviation for repeatability and reproducibility experiments were compared to similar results obtained by the use of UV-Vis spectrophotometry, and the results showed that the voltammetric procedure using HMDE is suitable to determine pharmaceutical compounds in complex samples. The applicability of the proposed procedure was tested on pharmaceutical formulations of NIM and OFX by observing the stability, specificity, recovery and precision of the procedure in tablets, oral solution and ophthalmic solution.     

Determination of naproxen in pharmaceutical preparations by room-temperature phosphorescence. A comparative study of several organized media.

Different methods for the determination of naproxen by room-temperature phosphorescence (RTP) using organized media such as cyclodextrins (beta-CD and gamma-CD) and micelles (Triton X-100 and sodium dodecyl sulfate) are reported. The inclusion complexes formed between both beta- and gamma-cyclodextrins and naproxen were previously investigated at both acid and basic pH by spectrofluorimetry. In both cases, 1:1 guest-host stoichiometries were established and the corresponding association constants were calculated. Different systems were examined with the purpose of obtaining phosphorescent emission from naproxen solutions, and the best signals were obtained when naproxen was in the presence of beta-CD-cyclohexane-Tl(I), gamma-CD-1,3-dibromopropane, Triton X-100-Tl(I) and SDS-Tl(I), respectively. In all cases, sodium sulfite was used as deoxygenator. The use of an inorganic compound (thallium nitrate) as a heavy-atom source in a cyclodextrin system represents a novel finding. Surface response optimization approaches were carried out to optimize the chemical variables which have an influence on the RTP emission of naproxen. Based on the results obtained, univariate RTP calibration methods for the determination of the analyte in pharmaceutical preparations were satisfactorily developed. In one case, the standard additions method was applied to a mixture of naproxen and the antibiotic tetracycline.     

Polarographic determination of chlorquinaldol in pharmaceutical preparations

A polarographic method for chlorquinaldol (5,7-dichloro-2-methyl-8-hydroxyquinoline) determination, based on the main cathodic wave, has been developed in acidic medium and it has been applied to pharmaceutical preparations. The obtained results show good accuracy; the relative standard deviation is ± 0.013.     

Kinetic determination of codeine in pharmaceutical preparations

A kinetic method for the determination of codeine, based on its inhibitor action on the catalytic decomposition of hydrogen peroxide by cobalt(II), is presented. It has been found that the effect of codeine is most pronounced in the presence of 5% v/v ethylene glycol. The reaction is followed photometrically. Codeine can be determined in concentrations ranging from 0.80×10^–5 M to 2.4×10^–5 M. The method has been applied to the determination of codeine in pharmaceutical preparations.     

Spectrofluorimetric determination of clioquinol in pharmaceutical preparations

Summary The absorption spectrum of the nitrate radical (NO₃) in aqueous solution and the kinetic of the reactions with Cl^– and OH^– have been determined using laser-spectrometric techniques. The maximum absorption was found at 635 nm with a decadic absorption coefficient of =(530±110) l/mol·cm. At 298 K rate constants of k₁=(1.0±0.2)·10⁷ l/mol·s for the reaction with chloride and of k₂=(8.2±0.9)·10⁷ l/mol·s for the reaction with hydroxide were obtained.     

Spectrofluorimetric determination of fluoroquinolones in pharmaceutical preparations

Simple, rapid and highly sensitive spectrofluorimetric method is presented for the determination of four fluoroquinolone (FQ) drugs, ciprofloxacin, enoxacin, norfloxacin and moxifloxacin in pharmaceutical preparations. Proposed method is based on the derivatization of FQ with 4-chloro-7-nitrobenzofurazan (NBD-Cl) in borate buffer of pH 9.0 to yield a yellow product. The optimum experimental conditions have been studied carefully. Beer's law is obeyed over the concentration range of 23.5-500 ng mL(-1) for ciprofloxacin, 28.5-700 ng mL(-1) for enoxacin, 29.5-800 ng mL(-1) for norfloxacin and 33.5-1000 ng mL(-1) for moxifloxacin using NBD-Cl reagent, respectively. The detection limits were found to be 7.0 ng mL(-1) for ciprofloxacin, 8.5 ng mL(-1) for enoxacin, 9.2 ng mL(-1) for norfloxacin and 9.98 ng mL(-1) for moxifloxacin, respectively. Intra-day and inter-day relative standard deviation and relative mean error values at three different concentrations were determined. The low relative standard deviation values indicate good precision and high recovery values indicate accuracy of the proposed methods. The method is highly sensitive and specific. The results obtained are in good agreement with those obtained by the official and reference method. The results presented in this report show that the applied spectrofluorimetric method is acceptable for the determination of the four FQ in the pharmaceutical preparations. Common excipients used as additives in pharmaceutical preparations do not interfere with the proposed method.     

Colorimetric determination of pyridoxine in pharmaceutical preparations

Summary The USP method for the determination of pyridoxine hydrochloride in pharmaceutical preparations has been modified to increase the stability of the colour, the speed of determination and the sensitivity. The reaction is carried out in propan-2-ol medium instead of water triethanolamine is used as the buffer, and iodine is used as oxidant when necessary. The colour is stable for about 45 min, the sensitivity of the reaction is greatly increased and the method takes only about a fifth of the time of the USP method.

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Kolorimetrische Bestimmung von Pyridoxin in pharmazeutischen Präparaten

Zusammenfassung Die USP-Methode zur Bestimmung von Pyridoxinhydrochlorid in pharmazeutischen Präparaten wurde modifiziert, um die Beständigkeit der Farbe, die Geschwindigkeit der Bestimmung und deren Empfindlichkeit zu verbessern. Statt in Wasser wird die Reaktion in Propan-2-ol durchgeführt, wobei Triethanolamin als Puffer und Jod — wenn nötig — als Oxydationsmittel verwendet werden. Die Farbe ist ungefähr 45 min beständig, die Empfindlichkeit der Reaktion stark verbessert und die zur Durchführung der Methode erforderliche Zeit beträgt etwa ein Fünftel im Vergleich zur USP-Methode.

     

Polarographic determination of chlorhexidine in pharmaceutical preparations

The electroreduction of chlorhexidine has been studied by d.c, a.c. and pulse polarography. Polarograms of the drug recorded from ammonium acetate buffers exhibit a single well-defined wave. The current is diffusion-controlled and proportional to the concentration. The reduction wave is due to an irreversible 8-electron reduction of the four> C=NH groups in the molecule to amino groups. The drug is strongly adsorbed on the electrode surface over a considerable potential range. Hence, the drug can be determined by polarography in the presence of other weaker surfactants often present in pharmaceutical formulations. Procedures have been proposed for pulse-polarographic determination of the drug in antiseptic cream and liquids. The proposed method is simple and accurate and does not involve time-consuming separation of the drug from insoluble constituents present in the sample.     

Polarographic determination of loratadine in pharmaceutical preparations

Loratadine, a potent antihistamine drug, is not directly electroreducible at a dropping mercury electrode; however, by means of a nitration procedure it is possible to obtain a nitro-loratadine derivative which has been identified as 4-(8-chloro-7-nitro-5,6-dihydro-11 H-benzo-[5,6]-cyclohepta-[l,2-b]-pyridin-l l-ylidene)-1-piperidine carboxylic acid ethyl ester. The electrochemical reduction of this derivative at different pHs and concentrations using polarography and cyclic voltammetry was studied. The derivative exhibits a differential pulse polarographic peak due to the reduction of the nitro group. This peak was used in order to develop an analytical procedure for determining loratadine in pharmaceutical dosage forms.

The recovery study shows adequate accuracy and precision for the developed assay and the excipients do not interfere in the determination.