Abdulrahman A. Al-Majed

Specific spectrofluorometric quantification of d-penicillamine in bulk and dosage forms after derivatization with 4-fluoro-7-nitrobenzo-2-oxa-1,3-diazole

A specific and sensitive fluorometric method is proposed for the determination of d-penicillamine in pure form and pharmaceuticals. The method is based on coupling between d-penicillamine and 4-fluoro-7-nitrobenzo-2-oxa-1,3-dizole (NBD-F) to produce the corresponding fluorescent NBD-penicillamine. The optimum conditions for the reaction were carefully investigated and incorporated into the procedure. The reaction was proceeded in borate buffer (pH 7.2) containing 20% of ethanol to give intense fluorescence having its excitation and emission wavelengths at 465 and 530 nm, respectively. The fluorescence intensity was a linear function of the drug concentration over the range of 0.6‐3 m gm l 1 . Regression analysis of the concentration fluorescence intensity showed good correlation ( r D 0.9975) with a detection limit of 2 10 3 m gm l 1 (1.3 10 8 M). The mean of percentage recoveries of added authentic drug was 100.00 1.05. The method was applied successfully to the determination of this drug in pharmaceutical dosage form. The mean recovery for the commercial capsules was 98.1 0.54%. The results were sufficiently accurate, precise and comparable with those obtained from the official method. The method is specific for the intact drug, and can be adopted in the presence of possible interferences. ©2000 Elsevier Science B.V. All rights reserved.

Voltammetric determination of isoxsuprine and fenoterol in dosage forms and biological fluids through nitrosation

A simple and highly sensitive voltammetric method was developed for the determination of isoxsuprine HCl (I) and fenoterol HBr (II) in dosage forms and biological fluids. The method is based on treatment of the two compounds with nitrous acid followed by measuring the cathodic current produced by the resulting nitroso derivatives. The voltammetric behavior was studied adopting Direct Current (DCt), Differential Pulse (DPP) and Alternating Current (ACt) polarography. Both compounds produced well-defined, diffusion-controlled cathodic waves over the whole pH range in Britton-Robinson buffers (BRb). At pH 11 and pH 9, the values of diffusion-current constants (Id), were 9.4 +/- 0.3 and 7.7 +/- 0.4 for I and II, respectively. The current-concentration plots for I were rectilinear over the range of 0.6-12 microg/ml and 0.1-12 microg/ml in the DCt and DPP modes, respectively. As for II, the range was 1-20 microg/ml and 0.1-20 microg/ml in the DCt and DPP modes, respectively. The minimum detectability (S/N = 2) were 0.02 microg/ml (approximately 6 x 10(-8) M) and 0.01 microg/ml (approximately 2.6 x 10(-8) M) for I and II, respectively, adopting the DPP mode. The proposed method was applied to the determination of both compounds in dosage forms and the results obtained were in good agreement with those obtained using reference methods. The proposed method was further applied to the determination of isoxsuprine in spiked human urine and plasma. The percentage recoveries adopting the DPP mode were 98.84 +/- 1.18 and 99.26 +/- 0.97, respectively.

Development of square-wave adsorptive stripping voltammetric method for determination of acebutolol in pharmaceutical formulations and biological fluids

A validated simple, rapid, sensitive and specific square-wave voltammetric technique is described for the determination of acebutolol (AC) following its accumulation onto a hanging mercury drop electrode in a Britton-Robinson universal buffer of pH 7.5. The optimal procedural conditions were: accumulation potential Eacc = - 0.8 V versus Ag/AgCl/KCl, accumulation duration tacc = 30 s, pulse-amplitude = 70 mV, scan rate = 100 mV/s, frequency = 30 Hz, surface area of the working electrode = 0.6 mm2 and the convection rate = 2000 rpm. Under these optimized conditions, the adsorptive stripping voltammetry (AdSV) peak current was proportional over the concentration range 5 × 10-7 - 6 × 10-6 M (r = 0.999). Recoveries for acebutolol from human plasma and urine were in the range 97-103% and 96-104% respectively. The method proved to be precise (intra-day precision expressed as %RSD in human plasma ranged from 2.9 - 3.2% and inter-day precision expressed as %RSD ranged from 3.4 - 3.8%) and accurate (intra-day accuracies expressed as % error in human urine ranged from -3.3 - 2.8% and inter-day accuracies ranged from -3.3 - 1.7%). The limit of quantitation (LOQ) and limit of detection (LOD) for acebutolol were 1.7 × 10-7 and 5 × 10-7 M, respectively. Possible interferences by substances usually present in the pharmaceutical formulations were investigated with a mean recovery of 101.6 ± 0.64%. Results of the developed square-wave adsorptive stripping voltammetry (SW-AdSV) method were comparable with those obtained by reference analytical method.

A direct HPLC method for the resolution and quantitation of the R-(−)- and S-(+)-enantiomers of vigabatrin (γ-vinyl-GABA) in pharmaceutical dosage forms using teicoplanin aglycone chiral stationary phase

A direct chiral high-performance liquid chromatography (HPLC) method was developed and validated for the resolution and quantification of antiepileptic drug enantiomers, R-(-)- and S-(+)-vigabatrin (gamma-vinyl-gamma-aminobutyric acid) in pharmaceutical products. The separation was optimized on a macrocyclic glycopeptide antibiotic chiral stationary phase (CSP) based on teicoplanin aglycone, chirobiotic (TAG), using a mobile phase system containing ethanol-water (80:20, v/v), at a flow rate of 0.4ml/min and UV detection set at 210nm. The stability of vigabatrin enantiomers under different degrees of temperature was also studied. The enantiomers of vigabatrin were separated from each other. The calibration curves were linear over a range of 100-1600microg/ml (r=0.999) for both enantiomers. The overall recoveries of R-(-)- and S-(+)-vigabatrin enantiomers from pharmaceutical products were in the range of 98.3-99.8% with %RSD ranged from 0.48 to 0.52%. The limit of quantification (LOQ) and limit of detection (LOD) for each enantiomer were 100 and 25microg/ml, respectively. No interferences were found from commonly co-formulated excipients.

A novel analytical approach for reducing the consumption of organic solvents in the charge transfer-based spectrophotometric analysis: Application in the analysis of certain antihypertensive drugs

A novel analytical approach for reducing the consumption of organic solvents in the charge transfer-based spectrophotometric analysis: Application in the analysis of certain antihypertensive drugs The present study describes the development of a novel analytical approach that can reduce by 50-fold the consumption of organic solvents in the charge transfer (CT)-based spectrophotometric analysis. The proposed approach employed 96-microwell assay plates for carrying out the reaction. The CT reaction between the electron-donating analyte and electron-accepting reagent was performed in microwells (200-μL of organic solvent) and the color signals were measured with a microwell-plate reader. Optimum conditions for the proposed approach were established for two antihypertensive drugs, namely ramipril (RML) and lisinopril (LSL) as model compounds for the electron-donating analytes, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as a π-electron acceptor. Under the optimum conditions, Beers law was obeyed in the concentration range of 6-100 and 6-60 μg mL-1 for RML and LSL, respectively. The limits of detection were 0.97 and 1.10 μg mL-1 for RML and LSL, respectively. The precision of the methods was satisfactory; the values of relative standard deviations did not exceed 1.1 %. The proposed approach was successfully applied to the analysis of pharmaceutical dosage forms with good accuracy and precision. The results were comparable with those of the reported methods. The approach described herein is of great practical value in pharmaceutical analysis because it reduces the exposure of analysts to the toxic effects of organic solvents, lowers the analysis cost by 50-fold, and it has a high throughput property. Although the approach was validated for RML and LSL, the same methodology could be used for any electron-donating analyte for which a CT-reaction can be performed. Novi analitički pristup sa smanjenom potrošnjom organskih otapala u spektrofotometrijskoj analizi temeljenoj na prijenosu naboja: Primjena u analizi nekih antihipertenziva U radu je opisan razvoj novog analitičkog pristupa koji 50 puta smanjuje potrošnju organskih otapala u spektrofotometrijskoj analizi na bazi prijenosa naboja (CT). Predložena metoda koristi ploče s 96 jažica za izvođenje analize. CT reakcije između elektron-donora i elektron-akceptora izvode se u jažicama s 200-μL organskog otapala. Promjene boje mjere se pomoću posebnog mikročitača za ploče s jažicama. Određeni su optimalni uvjeti za dva antihipertenzivna lijeka, ramipril (RML) i lizinopril (LSL) koji su upotrebljeni kao modelni spojevi za elektron-donorske analite, i 2,3-diklor-5,6-dicijano-1,4-benzokinon (DDQ) kao π-elektronski akceptor. U optimalnim uvjetima Beerov zakon je vrijedio u koncentracijskom području 6-100 i 6-60 μg mL-1 za RML, odnosno LSL. Granice detekcije bile su 0,97 i 1,1 μg mL-1 za RML, odnosno LSL. Preciznost metode bila je zadovoljavajuća, a relativna standardna devijacija bila je manja od 1,1 %. Predložena metoda uspješno je primijenjena za analizu doziranih farmaceutskih pripravaka koji sadrže ispitivane lijekove, uz dobru točnost i preciznost. Rezultati predložene metode usporedivi su s rezultatima poznatih metoda. Postupak opisan u ovom radu vrlo je praktičan: analitičari su manje izloženi toksičnim učincima organskih otapala, troškovi analize smanjeni su 50 puta, a također ju odlikuje visoka propusnost. Iako je postupak validiran za RML i LSL, ista metoda može se upotrijebiti za elektron-donirajući analit koji ulazi u CT reakciju.

A Derivatization Reagent for Vigabatrin and Gabapentin in HPLC with Fluorescence Detection

Abstract A validated, selective, and sensitive chromatographic method for determination of two antiepileptic drugs, vigabatrin (VGA) and gabapentin (GBA) has been developed. Determination was obtained by pre‐column reaction of the samples with fluorescamine and separating the corresponding derivatives with a reverse phase HPLC on a 5 micro ASMT BANsil CN column and fluorescence detection (λex 390 nm, λem 472 nm). Acetonitrile‐TBAH (20∶80) containing phosphoric acid was used as mobile phase. A linear quantitative response curve was generated over a concentration range of 0.2–1.0 µg/mL with a correlation coefficient of 0.999 and 0.995 for vigabatrin and gabapentin, respectively. The percentage recovery of vigabatrin from spiked plasma was 102.7 with RSD% of 4.51. Validation of accuracy and precision were satisfactory for both drugs within‐and between‐run assay. The method is specific for the intact drugs, and can be adopted in the presence of possible interferences.

HPLC-fluorescence method for the enantioselective analysis of propranolol in rat serum using immobilized polysaccharide-based chiral stationary phase.

A stereoselective high-performance liquid chromatographic (HPLC) method was developed and validated to determine S-(-)- and R-(+)-propranolol in rat serum. Enantiomeric resolution was achieved on cellulose tris(3,5-dimethylphenylcarbamate) immobilized onto spherical porous silica chiral stationary phase (CSP) known as Chiralpak IB. A simple analytical method was validated using a mobile phase consisted of n-hexane-ethanol-triethylamine (95:5:0.4%, v/v/v) at a flow rate of 0.6 mL min(-1) and fluorescence detection set at excitation/emission wavelengths 290/375 nm. The calibration curves were linear over the range of 10-400 ng mL(-1) (R = 0.999) for each enantiomer with a detection limit of 3 ng mL(-1). The proposed method was validated in compliance with ICH guidelines in terms of linearity, accuracy, precision, limits of detection and quantitation, and other aspects of analytical validation. Actual quantification could be made for propranolol isomers in serum obtained from rats that had been intraperitoneally (i.p.) administered a single dose of the drug. The proposed method established in this study is simple and sensitive enough to be adopted in the fields of clinical and forensic toxicology. Molecular modeling studies including energy minimization and docking studies were first performed to illustrate the mechanism by which the active enantiomer binds to the β-adrenergic receptor and second to find a suitable interpretation of how both enantiomers are interacting with cellulose tris(3,5-dimethylphenylcarbamate) CSP during the process of resolution. The latter interaction was demonstrated by calculating the binding affinities and interaction distances between propranolol enantiomers and chiral selector.

PVC Membrane Sensors for Potentiometric Determination of Acebutolol

The construction and general performance characteristics of two novel potentiometric membrane sensors responsive to the acebutolol are described. The sensors are based on the use of ion-association complexes of acebutolol (AC) with tetraphenylborate(TPB) (I) and phosphomolybdate(PM) (II) as exchange sites in a PVC matrix. The sensors show a fast, stable and near- Nernstian for the mono charge cation of AC over the concentration range 1×10-3 - ∼10-6 M at 25 °C over the pH range 2.0 - 6.0 with cationic slope of 51.5 ± 0.5 and 53.0 ± 0.5 per concentration decade for AC-I and AC-II sensors respectively. The lower detection limit is 6×10-6 M and 4×0-6 M with the response time 20-30 s in the same order of both sensors. Selectivity coefficients of AC related to a number of interfering cation and some organic compounds were investigated. There are negligible interferences are caused by most of the investigated species. The direct determination of 3 - 370 μg/ml of AC shows an average recovery of 99.4 and 99.5% and a mean relative standard deviation of 1.5% at 100.0 μg/ml for sensor I and II respectively. The results obtained by determination of AC in tablets using the proposed sensors which comparable favorably with those obtained by the British pharmacopoeia method. In the present investigation the electrodes have been utilized as end point indicator for some precipitation titration reactions.

Use of mixed anhydrides for the determination of terfenadine in dosage forms and spiked human plasma

Terfenadine reacts with mixed anhydrides (malonic and acetic anhydrides) producing a yellow-coloured product with intense fluorescence. Based on this fact, a spectrophotometric method was developed for the determination of terfenadine in dosage forms. The relation between the absorbance at 395 nm and the concentration is rectilinear over the range 0.5-5 microg ml(-1) (molar absorptivity is 1.405 x 10(5) l mol(-1) cm (-1)). The reaction product was also measured spectrofluorimetrically at 435 nm after excitation at 395 nm. The fluorescence intensity was directly proportional to the concentration over the range 0.5-4 ng ml(-1) with minimum detectability (S/N = 2) of 0.07 microg ml(-1) (approximately 1.5 x 10(-10) M). The different parameters affecting the development and stability of the reaction product were carefully studied and incorporated into the procedure. The proposed spectrophotometric method was successfully applied to the determination of terfenadine in tablets and suspensions; the percentage recoveries were 99.83 +/- 0.75 and 99.65 +/- 0.83, respectively. The proposed spectrofluorimetric method was applied to the determination of terfenadine in spiked human plasma. The percentage recovery was 99.35 +/- 2.19. The method is highly sensitive and specific. No interference was noticed from co-formulated drugs, such as pseudoephedrine and ibuprofen.

The voltammetric behavior of nizatidine and its determination in biological fluids.

The voltammetric behavior of nizatidine (a newly introduced antiulcer drug) was studied using direct current (DCt), alternating current and differential pulse polarography (DPP). Well-defined cathodic waves were obtained over the whole pH range in Britton-Robinson buffers, in addition to 0.1 and 1 M HCl media. The main reduction wave was characterized as being irreversible and diffusion-controlled, although adsorption phenomena played a limited role in the electrode process. The current-concentration relationship was found to be rectilinear over the range 1x10(-5)-6x10(-4) and 2x10-6) -2x10(-4) M using DCt and DPP modes respectively, with a minimum detectability (S/N = 2) of 2x10(-7) M using the latter technique. The number of electrons involved in the reduction process was established, and the mechanism of electrode reaction was verified. The proposed method was successfully applied to determination of nizatidine in spiked human plasma and urine and the percentage recoveries were 96.12+/-0.40 and 97.12+/-0.17, respectively.