Sameer A. M. Abdulrahman

Sensitive and Selective Spectrophotometric Determination of Gabapentin in Capsules Using Two Nitrophenols as Chromogenic Agents

Two simple and selective spectrophotometric methods have been proposed for the determination of gabapentin (GBP) in pure form and in capsules. Both methods are based on the proton transfer from the Lewis acid such as 2,4,6-trinitrophenol (picric acid; PA) or 2,4-dinitrophenol (2,4-DNP) to the primary amino group of GBP which works as Lewis base and formation of yellow ion-pair complexes. The ion-pair complexes formed show absorption maximum at 415 and 420 nm for PA and 2,4-DNP, respectively. Under the optimized experimental conditions, Beers law is obeyed over the concentration ranges of 1.25–15.0 and 2.0–18.0 μg mL−1 GBP for PA and 2,4-DNP methods, respectively. The molar absorptivity, Sandells sensitivity, detection and, quantification limits for both methods are also reported. The proposed methods were applied successfully to the determination of GBP in pure form and commercial capsules. Statistical comparison of the results was performed using Students t-test and F-ratio at 95% confidence level, and there was no significant difference between the reference and proposed methods with regard to accuracy and precision. Further, the validity of the proposed methods was confirmed by recovery studies via standard addition technique.

Sensitive and selective spectrophotometric assay of gabapentin in capsules using sodium 1, 2-naphthoquinone-4-sulfonate.

A simple, sensitive, and selective spectrophotometric method has been developed for the determination of gabapentin (GBP) in capsules. The method is based on the reaction of GBP and sodium 1,2-naphthoquinone-4-sulfonate (NQS) in the presence of Clark and Lubs buffer of pH 11 to form an orange-coloured product which was measured at 495 nm. The parameters that affect the reaction were carefully optimized and under the optimized conditions, linear relationship was obtained in the concentration range of 7.5-75 µg ml(-1) GBP. The molar absorptivity, limits of detection (LOD) and quantification (LOQ) and Sandell sensitivity are also reported. The proposed method was successfully applied to the determination of GBP in capsules with good accuracy and precision and without detectable interference from common excipients. The reliability of the proposed method was further established by parallel determination by the reference method and also by recovery studies. The reaction mechanism is proposed and discussed.

Spectrophotometric determination of ethionamide in pharmaceuticals using Folin–Ciocalteu reagent and iron(III)-ferricyanide as chromogenic agents

Abstract Two simple and sensitive spectrophotometric methods are described for the determination of ethionamide (ETM) in pure drug and tablets. The first method is based on the reduction of Folin–Ciocalteu (F–C) reagent by ETM in sodium carbonate medium to form a blue coloured complex, which was measured at 760 nm (Molybdenum–tungsten blue method). In the second method (Prussian blue method), iron(III) was reduced to iron(II) by ETM in HCl medium, in which iron(II) was complexed with ferricyanide, and the resulting Prussian blue was also measured at 760 nm. The absorbance measured in each case was related to the ETM concentration. The experimental conditions were carefully studied and optimised. Beer’s law was obeyed in concentration ranges of 1–40 μg/ml and 0.2–4.0 μg/ml with the Molybdenum-tungsten blue method and the Prussian blue method, respectively, with corresponding molar absorptivity values of 5.72 × 103 and 3.18 × 104 l/(mol·cm). The limits of detection (LOD) and quantification (LOQ) were 0.09 and 0.27 μg/ml for the Molybdenum-tungsten blue method and 0.01 and 0.04 μg/ml for the Prussian blue method. Within-day and between-day relative standard deviations (%RSD) at three different concentration levels were <3%, and the respective relative errors (%RE) were ≤2%, implying good accuracy and precision of the methods. The proposed methods were successfully applied to the determination of ETM in bulk powder and tablets, and the results demonstrated that the methods were as accurate and precise as the official method.

Spectrophotometric assay of diethylcarbamazine citrate in pharmaceuticals and human urine via ion-pair reaction using methyl orange dye

Two simple and moderately selective spectrophotometric methods are described for the determination of Diethylcarbamazine Citrate (DEC) in bulk drug, dosage forms and spiked human urine. The first method (method A) is based on the formation of yellow colored ion-pair complex between DEC and Methyl Orange (MO) dye, at pH 4.95 ± 0.05, which was extracted into chloroform and measured at 420 nm. The second method (method B) involved the breaking of yellow ion-pair complex in acid medium followed by the measurement of the free dye at 520 nm. Experimental parameters influencing the formation and extraction of the ion-pair complex in method A and breaking of the complex in method B were scrupulously examined and optimized. Beer’s law is obeyed over the concentration ranges of 10-90 and 5-100 μg mL-1 DEC with corresponding molar absorptivity values of 2.90×103 and 3.54×103 L mol-1 cm-1 for method A and method B, respectively. The Sandell’s sensitivity values were 0.1351 and 0.1106 μg cm-2 for method A and method B, respectively. The Limits of Detection (LOD) and Quantification (LOQ) were calculated to be 0.36 and 1.09 μg mL-1 (method A) and 0.34 and 1.02 μg mL-1 (method B). The composition of drug-dye ion-pair complex used in method A was found to be 1:1 by Job’s method of continuous variations. The proposed methods were validated for robustness, ruggedness and selectivity, and applied to the determination of DEC in tablet, syrup formulations and spiked human urine samples. The results demonstrated that the proposed methods are as accurate and precise as the reference method. The accuracy of the methods was further ascertained by recovery study via standard-addition method.

Use of picric acid and iodine as electron acceptors for spectrophotometric determination of lansoprazole through a charge-transfer complexation reaction

Abstract This article describes the development of two simple and selective spectrophotometric methods for the determination of lansoprazole (LAN), an irreversible proton pump inhibitor, in both pure drug and capsule formulations. The methods are based on the formation of charge-transfer (CT) complexes between LAN an electron donor and either picric acid or iodine as an electron acceptor. The intensely coloured products formed were quantified based on the absorption bands at 410 nm for picric acid (method A) and 360 nm for iodine (method B). The accuracy and precision of the methods were evaluated on intra-day and inter-day bases. Beer’s law is obeyed in the concentration ranges of 2–32 and 0.8–12.0 μg/ml LAN for method A and method B, respectively. The molar absorptivity values, limits of detection (LOD) and limits of quantification (LOQ) have also been reported. The reaction stoichiometry for both methods was evaluated by Job’s method of continuous variation and was found to be 1:1 (LAN: picric acid and LAN: iodine). The proposed methods were successfully applied to the determination of LAN in capsules with good accuracy and precision and without a detectable interference from common excipients. A statistical comparison of the methods revealed that there is no significant difference between the official method and the proposed methods.

Application of Cerium (IV) as an Oxidimetric Agent for the Determination of Ethionamide in Pharmaceutical Formulations

Two simple methods are described for the determination of ethionamide (ETM) in bulk drug and tablets using cerium (IV) sulphate as the oxidimetric agent. In both methods, the sample solution is treated with a measured excess of cerium (IV) solution in H2SO4 medium, and after a fixed standing time, the residual oxidant is determined either by back titration with standard iron (II) solution to a ferroin end point in titrimetry or by reacting with o-dianisidine followed by measurement of the absorbance of the orange-red coloured product at 470 nm in spectrophotometry. In titrimetry, the reaction proceeded with a stoichiometry of 1 : 2 (ETM : Ce (IV)) and the amount of cerium (IV) consumed by ETM was related to the latters amount, and the method was applicable over 1.0–8.0 mg of drug. In spectrophotometry, Beers law was obeyed over the concentration range of 0.5–5.0 μg/mL ETM with a molar absorptivity value of 2.66 × 104 L/(mol·cm). The limits of detection (LOD) and quantification (LOQ) calculated according to ICH guidelines were 0.013 and 0.043 μg/mL, respectively. The proposed titrimetric and spectrophotometric methods were found to yield reliable results when applied to bulk drug and tablets analysis, and hence they can be applied in quality control laboratories.

Application of ion-pair complexation reaction for the spectrophotometric determination of bupropion hydrochloride in pharmaceuticals.

This is the first report on the use of visible spectrophotometry for the determination of bupropion hydrochloride (BUPH), a second-generation antidepressant, in pharmaceuticals. Two sensitive, selective, and cost-effective spectrophotometric methods are described. The first method (method A) is based on the formation of yellow-coloured ion-pair complex between the BUPH and methyl orange (MO) at pH 3.80 ± 0.10 which was extracted into dichloromethane and the absorbance measured at 425 nm. The second method (method B) is based on the breaking of the yellow BUPH-MO ion-pair complex in acid medium followed by the measurement of the red-pink colour at 520 nm. Beers Law is obeyed over the concentration ranges of 1.00-12.0 and 0.48-7.20 µg ml(-1) BUPH for method A and method B, respectively. The molar absorptivities are calculated to be 2.18 × 10(4) and 3.79 × 10(4) l mol(-1) cm(-1) for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.0127 and 0.0073 µg cm(-2) . The limits of detection and quantification have also been reported. The proposed methods were applied successfully to the determination of BUPH in pure drug and commercial tablets. The accuracy and reliability of the proposed methods were further ascertained by recovery studies via standard addition technique.

Application of bromate-bromide mixture as a green brominating agent for the spectrophotometric determination of atenolol in pharmaceuticals

Two highly sensitive spectrophotometric methods are proposed for the quantification of atenolol (ATN) in pure drug as well as in pharmaceutical formulations. The methods are based on the bromination reaction of ATN with a known excess of bromate-bromide mixture in acid medium followed by the determination of unreacted bromine. The residual bromine is determined by its reaction with excess iodide and the liberated iodine (I3□) is either measured at 360 nm (method A) or reacted with starch followed by the measurement of the starch-iodine chromogen at 570 nm (method B). Under the optimum conditions, ATN could be assayed in the concentration ranges of 0.5-9.0 and 0.3-6.0μg mL-1 for method A and method B, respectively, with corresponding molar absorptivity values of 2.36×104 and 2.89×104 L/mol.cm. Sandell’s sensitivity values are found to be 0.0113 and 0.0092 μg/cm2 for method A and method B, respectively. The proposed methods were successfully applied to the analysis of different commercial brands of pharmaceutical formulations and the results obtained by the proposed methods were in good agreement with those obtained using the reference method. The reliability of the methods was further ascertained by recovery studies using standard- addition method.