Spectrophotometric and polarographic determination of enalapril and lisinopril using 2,4-dinitrofluorobenzene.

The reaction of enalapril maleate and lisinopril with 2,4-dinitrofluorobenzene has been used to form colored products and polarographically active derivatives. The different experimental conditions have been optimized. The proposed methods have been validated and applied to the determination of both drugs in their commercial tablets. The results have been statistically compared with those obtained using the official HPLC methods.

The utilization of copper(II) phosphate for the anodic stripping voltammetric assay of alendronate sodium, desferrioxamine mesylate and lisinopril.

A sensitive differential pulse anodic stripping voltammetric method is described for the determination of alendronate sodium, desferrioxamine mesylate and lisinopril. The procedure is based on the formation of labile drug-copper(II) complex when shaking with copper(II) phosphate suspension. The voltammetric peaks, which correspond to the reduction of the copper(II) moiety of the formed complexes are obtained at -153, -74 and -111 mV, respectively. The different experimental parameters have been carefully studied. The method has been fully validated. The limit of detection was as low as 8.6 ng ml(-1). The method has been applied successfully for the determination of the drugs in plasma and in their pharmaceutical preparations. The obtained results were compared statistically with those obtained from a published method, in case of AS, or the official USP methods, for the other two drugs.

Extraction-spectrophotometric determination of phenytoin in capsules and plasma using potassium permanganate/dicyclohexano-24-crown-8.

An extraction-spectrophotometric method for the determination of phenytoin in capsules and plasma is presented. The method is based upon oxidation of phenytoin using alkaline potassium permanganate solubilized in chloroform/cyclohexane (1:1) after crowning with dicyclohexano-24-crown-8 (DC-24-C-8). The formed benzophenone being soluble in the oxidation reaction medium was directly measured at 238 nm. The optimum conditions for the reaction were studied and the detection limit was found to equal 1.2 mg/100 ml. The developed method was applied to the determination of the drug in capsules and plasma. The method is simple, accurate and avoids laborious multistep extraction procedures.

Spectrophotometric analysis of some guanidino drugs by acid-dye and charge-transfer complexation methods.

Two spectrophotometric methods are described for the determination of guanethidine sulphate (I), guanfacine hydrochloride (II), guanoclor sulphate (III), guanoxan sulphate (IV) and debrisoquine sulphate (V). The first method involves ion-pair formation of the selected compounds (I-V) with bromocresol purple at pH 3.8. The yellow ion pair is extracted with chloroform and the absorbance is measured at about 415 nm. The second method is based on the reaction of the basic guanidino compounds (I, III-V) with iodine in chloroform to give molecular charge-transfer complexes with maximum absorbance at 292 and 345 nm. Beer's law was obeyed for both methods and the relative standard deviations were found to be less than 2%. The apparent molar absorptivities were found to be 2.1 x 10(4) to 6.9 x 10(4) l mol-1 cm-1 using bromocresol purple and 0.7 x 10(4) to 2.4 x 10(4) l mol-1 cm-1 using iodine. The investigated drugs were assayed in tablets. The mean percentage recoveries were found to be 99.8-100.8% by the acid-dye method and around 100.4% by the charge-transfer complexation method.

Spectrofluorimetric determination of guanethidine sulphate, guanoxan sulphate and amiloride hydrochloride in tablets and in biological fluids using 9,10-phenanthraquinone.

A highly sensitive spectrofluorimetric method for the determination of some drugs of the monosubstituted guanidine derivatives in laboratory made tablets, in spiked human serum and in urine samples is presented. The method is based on the reaction of guanethidine sulphate (I), guanoxan sulphate (II) and amiloride hydrochloride (III) with 9,10-phenanthraquinone (IV) to give highly fluorescent derivatives. The linearity ranges were found to be 0.06-0.96 mug/ml for (I) and (II) and 0.04-0.28 mug/ml for (III), with relative standard deviation less than 2%. Mean percentage recoveries for tablets were found to be 99.9 +/- 1.3, 100.5 +/- 1.1 and 100.0 +/- 1.6 for I, II and III, respectively. For I and III the results are highly correlated with the B.P. methods. Using the synchronous fluorimetry, differentiation between I and II was possible. Chloroform, dichloromethane and ethyl acetate have been used to extract I, II and III, respectively from serum and urine at basic pH, followed by applying the proposed fluorimetric method. Percentage recoveries were found to be 95.7-102.2%. The limit of detection is 0.04 mug/ml for I and II and 0.02 mug/ml for III.

Derivative spectrophotometric determination of antiprotozoal drugs in two-component tablet preparation.

First (D1-) and second (D2-) derivative spectrophotometric methods for the determination of diloxanide furoate and metronidazole in two-component preparation are presented. The methods are based on the direct measurements of diloxanide furoate in 0.1N hydrochloric acid solution at 262 nm and 248 nm for D1- and D2- curves, respectively without the interference of the coexisting component. Metronidazole, on the other hand is determined before and after its acid extraction from chloroformic solution and the subsequent D1- measurement at 288 nm and D2- measurement at 296 nm. The methods have been applied for the determination of both components in laboratory made mixtures and in tablet with a coefficient of variation less than 2%.

Spectrophotometric determination of cimetidine in the presence of its acid-induced degradation products.

Cimetidine has been determined in the presence of its acid-induced degradation products using a second derivative (D2-) spectrophotometric method (method I) or a colorimetric method (method II). The former is based on D2-value measurement at 216 nm, whilst the latter depends on charge-transfer complexation with dichlorophenol-indophenol. The two methods are proved to be stability indicating, since plots of log C% versus time were linear. The application to cimetidine determination in tablets and ampoules gave good results.

Computer-assisted spectrophotometry: multicomponent analysis with a discrete fourier transform.

A computer-assisted method for analysis of multicomponent mixtures by use of conventional absorbance as well as discrete Fourier transforin coefficients (combined trigonometric functions) is presented. The program can store absorbance data (A vs. lambda), process data by convolution with combined trigonometric functions, apply least-squares analysis and solve the resultant simultaneous linear equations, and display data on screen, printer or plotter.

Determination of chlorpheniramine maleate, dihydrocodeine bitartrate and ephedrine hydrochloride in cough mixture by derivative and differential spectrometry.

A method is presented for the determination of chlorpheniramine maleate, dihydrocodeine bitartrate and ephedrine hydrochloride in a three-component mixture without prior separation. Chlorpheniramine maleate was determined by the first and second derivative-differential spectrophotometry, while dihydrocodeine bitartrate was directly determined using first and second derivative measurements. Ephedrine hydrochloride could be determined by first and second derivative spectrophotometry after its oxidation with sodium metaperiodate. The method was proved using synthetic mixtures of these drugs and was applied for their determination in syrup with a coefficient of variation less than 2%.

Colorimetric determination of some penicillins and cephalosporins with 2-nitrophenylhydrazine hydrochloride.

A simple and sensitive calorimetric method for the determination of some penicillins and cephalosporins is presented. The method is based on reaction with 2-nitrophenylhydrazine hydrochloride in presence of dicyclohexylcarbodi-imide and pyridine. The violet colour of the resulting acid hydrazide is measured at the appropriate wavelength. The method has been applied to determination of these antibiotics in bulk and dosage forms, with a coefficient of variation less than 2%.

Derivative spectrophotometric determination of clotrimazole in single formulations and in combination with other drugs.

First (D1) and second (D2) derivative spectrophotometric methods are presented for the determination of clotrimazole after its acid hydrolysis. Mixtures of clotrimazole with azidamfenicol and dexamethasone have been assayed using D2 measurement at 302 nm after acid hydrolysis for clotrimazole, D1 measurement at 288 nm for azidamfenicol, and D1 measurement at 436 nm after reaction with phenylhydrazinium sulfate for dexamethasone. Reproducible results with relative standard deviations of less than 2% are obtained. The proposed method has been successfully applied to the analysis of creams, topical solutions, and vaginal tablets.