Green HPTLC and stability-indicating RP-HPLC for the assay of dextromethorphan hydrobromide and menthol in their lozenges.

Two chromatographic methods were developed for the assay of the FDA approved lozenges containing dextromethorphan hydrobromide (DXT) and menthol (MNT). The first was a green HPTLC method which uses a mobile phase of methanol-ammonia (10:0.1, v/v). The densitometric measurements of the spots which were retained at 0.28±0.01 for DXT and 0.76±0.02 for MNT was done at 210nm. The other method was RP-HPLC method with stability indicating merits at which a mixture of 20mM phosphate buffer pH 3 and acetonitrile as mobile phase in isocratic mode was used. The cited drugs were resolved in RP-HPLC method using isocratic elution using 20mM phosphate buffer: acetonitrile (65:35 v/v) with retention times of 2.21 and 3.47min for MNT and DXT, respectively and quantified using 215nm. Both methods were entirely validated and both methods were successfully able to analyze both drugs in presence of lozenges inactive ingredients. HPLC method had the advantage of being stability indicating at which resolution of the drugs from their forced degradation products was successfully attained. For HPTLC method, both drugs showed reasonable RF values when compared to rapidly eluted MNT in RP-HPLC; also it was more environmentally friendly than RP-HPLC as it used solvents which are less toxic and greener.

Spectral and polarographic determination of eprosartan. Kinetic studies of the oxidation of eprosartan using a platinum electrode.

Two simple and sensitive methods are presented for the determination of eprosartan in pharmaceutical preparations. The first method, spectrophotometry, was based on the oxidation of this drug by ammonium cerium (IV) nitrate in the presence of perchloric acid with subsequent measurement of the absorbance at 326 nm; this principle was adopted to develop a kinetic method for the determination of eprosartan in dosage forms. The second method, differential pulse polarography, was based on measuring the peak height at -1300 mV, corresponding to the reduction of the drug in Britton-Robinson buffer (pH 3). The proposed methods proved to be accurate and precise and can be applied for the routine analysis of this drug in commercial dosage forms, without interference from the excipients. The work was extended to study the electrochemical oxidation of eprosartan at different electrolysis currents (10-40 mA). The electrochemical decomposition products were characterized by UV/visible spectroscopy; the decomposition rates follow first order reactions and increase with raising the current. The degradation was found to be faster in basic than acidic medium. The thermodynamics for electrochemical decomposition were also evaluated at different pH values.

Spectrophotometric and titrimetric determination of nizatidine in capsules.

Four simple and accurate methods are described for the determination of nizatidine (NIZ) in pharmaceutical preparations. The first method is based on the formation of an ion-pair complex between the drug and either of bromocresol purple or picric acid with subsequent measurement of the developed colors at 411 and 400 nm, respectively. The second method depends on the condensation of mixed anhydrides of citric acid/acetic anhydride, with the tertiary amino group of the drug, where the developed color is measured spectrophotometrically at 545 nm. The oxidation of nizatidine by N-bromosuccinimide was utilized as a basis for the titrimetric method for its assay in capsules. The last method depends on the oxidation of nizatidine by ammonium cerium IV sulfate in the presence of perchloric acid with subsequent measurement of the absorbance at 314 nm; this principle is adopted to develop a kinetic method for the determination of NIZ in capsules. All the reaction conditions have been studied. The detection limits were varied from 0.44 to 0.78 microg ml(-1). The proposed methods were successfully applied to the assay of nizatidine in capsules.

Determination of some histamine H1-receptor antagonists in dosage forms.

Three simple and accurate methods are presented for determination of Cetirizine, Fexofenadine, Loratadine and Acrivastine in pure form and commercial dosage forms. The first method is based on the reaction of the above cited drugs with bromocresol purple dye to form ion-pair complex extractable with chloroform and subsequently measured spectrophotometrically. Secondly, eosin gives with these drugs ion-pair complex, measurable directly without extraction both spectrophotometrically and spectrofluorimetrically. The last method involves the base-catalysed condensation of mixed anhydrides of organic acids (citric acid/acetic anhydride) where as the tertiary amino group in the above-cited drugs acts as the basic catalyst. The product of condensation is measured spectrophotometrically. All the reaction conditions for the proposed methods have been studied.

Spectrophotometric methods for the determination of benazepril hydrochloride in its single and multi-component dosage forms.

Three sensitive and accurate methods are presented for the determination of benazepril in its dosage forms. The first method uses derivative spectrophotometry to resolve the interference due to formulation matrix. The second method depends on the color formed by the reaction of the drug with bromocresol green (BCG). The third one utilizes the reaction of benazepril, after alkaline hydrolysis, with 3-methylbenzothialozone (MBTH) hydrazone where the produced color is measured at 593 nm. The latter method was extended to develop a stability-indicating method for this drug. Moreover, the derivative method was applied for the determination of benazepril in its combination with hydrochlorothiazide. The proposed methods were applied for the analysis of benazepril in the pure form and in tablets. The coefficient of variation was less than 2%.

Spectrophotometric and spectrofluorometric methods for the assay of lisinopril in single and multicomponent pharmaceutical dosage forms.

Simple and sensitive methods are described for the assay of lisinopril in tablets. The first method (A) is based on the reaction of the drug with chloranil in aqueous solution of pH 9.5 to give yellow colour measured at 346 nm. The second method (B) is based upon the interaction of lisinopril with dichlone resulting in the formation of an intense purple colour measured at 580 nm. The third method (C) depends on the reaction of the drug with acetylacetone and formaldehyde to form a coloured condensation product measured at 356 nm and also has a strong fluorescence at 475 nm (lambda(ex) 410 nm). This method is extended to determine lisinopril in binary mixtures with hydrochlorothiazide. The last method (D) depends on measuring the first and second derivative spectra of lisinopril. Moreover, the derivative method is used as stability-indicating method where lisinopril can be determined in presence of its degradation products. The proposed methods proved to be suitable for a rapid quality control of commercial dosage forms. The results obtained were precise and accurate.

Determination of dissociation constants of some pharmaceutical compounds using derivative spectrophotometry.

Derivative spectrophotometry is applied to the determination of the dissociation constants (pKa) of some weakly dissociating compounds. The pKa value(s) can be calculated by measuring the amplitude of derivative maxima (D) at the selected wavelengths for the dissociated, undissociated and partially dissociated forms of the compound. A graphical technique, based on plotting the derivative spectrophotometric titration curves and interpolating pKa at D1/2 is also presented. Both methods are applied to pharmaceutical compounds with single and double dissociation constants. The results are in good agreement with the reported pKa values of the investigated compounds.

Spectrophotometric determination of some 1,4-benzodiazepines by use of orthogonal polynomials.

A direct spectrophotometric method for the determination of some 1,4-benzodiazepines, namely, nitrazepam, prazepam and dipotassium chlorazepate, in the presence of their degradation products, is presented. The method depends upon the use of orthogonal polynomials, to eliminate interferences by degradation products to the absorption spectra of the intact drugs. The method was proved using synthetic mixtures of the intact drugs with their respective degradation products and its suitability to monitor for the stability of the drugs was demonstrated. The method has been applied to the determination of these drugs in dosage forms, with a coefficient of variation less than 2%.

Derivative spectrophotometric determination of some corticosteroids in combinations with other drugs.

Three 2-component mixtures, namely, dexamethazone-chlorpheniramine maleate, prednisolone-chlorpheniramine maleate, and prednisolone-salicylic acid, have been assayed using their first (D1) and second (D2) derivative spectra in methanol, delta absorption (delta A), and second derivative of delta A (delta D2) spectra in methanol-methanolic HCl. In the first 2 mixtures, chlorpheniramine maleate was determined by measuring its delta D2 value at 278 nm, while dexamethazone and prednisolone were analyzed by measuring their D1 values at 248 nm. Prednisolone and salicylic acid were analyzed in combination by using their respective D2 spectral responses at 272 and 314 nm. The results obtained are reasonably reproducible with a relative standard deviation less than 2%. The method has been successfully applied to the analysis of these drugs in their pharmaceutical formulations.

A sensitive colorimetric method for the determination of imipramine hydrochloride and desipramine hydrochloride.

A simple and rapid colorimetric method for the determination of imipramine hydrochloride and desipramine hydrochloride in their tablet formulations and in biological fluids is presented. The method is based on the reaction of these drugs with 3-methyl-2-benzothiazolone hydrazone in the presence of ferric chloride, with direct measurement at 635 nm. Cyclohexane was used to extract these drugs from serum and urine, at basic pH, by a single manual extraction. The method can detect 0.5 microgram/ml of each drug. The main advantages of this method are its simplicity and high sensitivity.

Determination of ethinyloestradiol in the presence of norethisterone by derivative-difference spectrophotometry.

A simple and direct method for the determination of ethinyloestradiol as a minor component in the presence of norethisterone and in oral contraceptive tablets is presented. The method is based on measuring the signal intensity, d delta A/d lambda and d2 delta A/d lambda 2, of the generated first and second derivative spectra of the delta-absorbance curves obtained by measuring solutions in methanol and methanol-sodium hydroxide at certain wavelengths. The method has been applied to the determination of ethinyloestradiol in oral contraceptive tablets, with a coefficient of variation of less than 2%.

Spectrophotometric determination of chloramphenicol-sulphacetamide in eye drops.

A rapid method for the determination of chloramphenicol in chloramphenicol-sulphacetamide drops is discussed. The method depends upon precipitating sulphacetamide as its silver salt by a solution of silver nitrate. Chloramphenicol is determined in the filtrate using the modified Vierordt's method. Sulphacetamide was determined by suitably diluting the drops with 0.01 N H2SO4 and then applying the modified Vierordt's method. The presence of macrogols proved not to interfere with the determination. Mean percentage recoveries +/- s.d. for chloramphenicol and sulphacetamide were found to be 100.8 +/- 0.95 and 100.2 +/- 1.0, respectively.