Hisham E. Abdellatef

Spectrophotometric and atomic absorption spectrometric determination of ramipril and perindopril through ternary complex formation with eosin and Cu(II)

Two sensitive, spectrophotometric and atomic absorption spectrometric procedures are developed for the determination of ramipril and perindopril. Both methods are based on the formation of a ternary complex, extractable with chloroform, between copper(II), eosin and the two cited drugs. Spectrophotometrically under the optimum condition, the ternary complexes showed an absorption maximum at 535 nm, with apparent molar absorptivities of 6.55 and 4.00 x 10(3) mol(-1) x cm(-1) and Sandells sensitivities of 5.80 x 10(-2) and 1.04 x 10(-1) microg x cm(-2) for perindopril and ramipril, respectively. The solution of ternary complex obeyed Beers law in concentration ranges 10-60 and 20-100 microg x ml(-1) for perindopril and ramipril, respectively. The proposed method was applied to the determination of the two cited drugs in pharmaceutical tablets. The atomic absorption spectrometric method, directly through the quantitative determination of copper content of the organic extract of the complex, was also investigated for the purpose of enhancing the sensitivity of the determination. The spectrophotometric and atomic absorption spectrometric procedures hold their accuracy and precision well when applied to the determination of ramipril and perindopril dosage forms.

Kinetic spectrophotometric determination of tramadol hydrochloride in pharmaceutical formulation.

Two simple and sensitive kinetic methods for the determination of tramadol hydrochloride are described. The first method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permanganate at room temperature for a fixed time at 20 min. The absorbance of the colored manganate ions was measured at 610 nm. The second method is based on the reaction of tramadol hydrochloride with 4-chloro-7-nitrobenzofurazan (NBD-Cl) in presence of 0.1 M sodium bicarbonate. The spectrophotometric measurements were recorded by measuring the absorbance at 467 nm, at fixed time at 25 min on thermostated water bath at 90+/-1 degrees C. All variables affecting the development of the colour have been investigated and the conditions were optimised. The absorbance concentration plots in both methods were rectilinear over the range 5-25 and 50-250 microg ml(-1), for the first and second methods, respectively. The two methods have been applied successfully to commercial capsule and ampoule dosage form. The results obtained are compared statistically with those given by the reference spectrophotometric method. The determination of tramadol hydrochloride by the fixed concentration and rate constant methods is feasible with the calibration equations obtained, but the fixed time method proves to be more applicable.

Spectrophotometric and AAS determination of ramipril and enalapril through ternary complex formation.

Two sensitive, spectrophotometric and atomic absorption spectrometric procedures are developed for the determination of two antihypertensive agents (enalapril maleate and ramipril). The spectrophotometric procedures for the two cited drugs are based on ternary complex formation. The first ternary complex (copper(II), eosin, and enalapril) was estimated by two methods; the first depends on its extraction with chloroform measuring at 533.4 nm. Beers law was obeyed in concentration range from 56 to 112 microg ml(-1). The second method for the same complex depends on its direct measurement after addition of methylcellulose as surfactant at the pH value 5 at 558.8 nm. The concentration range is from 19 to 32 microg ml(-1). The second ternary complex (iron(III), thiocyanate, and ramipril) was extracted with methylene chloride, measuring at 436.6 nm, with a concentration range 60-132 microg ml(-1). The direct atomic absorption spectrometric method through the quantitative determination of copper or iron content of the complex was also investigated for the purpose of enhancing the sensitivity of the determination. The spectrophotometric and atomic absorption spectrometric procedures hold their accuracy and precision well when applied to the determination of ramipril and enalapril dosage forms.

Spectrophotometric and atomic absorption spectrometric determination of certain cephalosporins.

Two sensitive spectrophotometric and atomic absorption spectrometric procedures are developed for the determination of certain cephalosporins (cefotaxime sodium and cefuroxime sodium). The spectrophotometric methods are based on the charge-transfer complex formation between these drugs as n-donors and 7,7,8,8-tetracyanoquinodimethane (TCNQ) or p-chloranilic acid (p-CA) as pi-acceptors to give highly coloured complex species. The coloured products are measured spectrophotometrically at 838 and 529 nm for TCNQ and p-CA, respectively. Beers law is obeyed in a concentration range of 7.6-15.2 and 7.1-20.0 microg x ml(-1) with TCNQ, 95.0-427.5 and 89.0-400.5 microg x ml-1 with p-CA for cefotaxime sodium and cefuroxime sodium, respectively. The atomic absorption spectrometric methods are based on the reaction of the above cited drugs after their alkali-hydrolysis with silver nitrate or lead acetate in neutral aqueous medium. The formed precipitates are quantitatively determined directly or indirectly through the silver or lead content of the precipitate formed or the residual unreacted metal in the filtrate by atomic absorption spectroscopy. The optimum conditions for hydrolysis and precipitation have been carefully studied. Beers law is obeyed in a concentration range of 1.9-11.4 and 1.78-8.90 microg x ml(-1) with Ag(I), 14.2-57.0 and 13.3-53.4 microg x ml-1 with Pb(II) for cefotaxime sodium and cefuroxime sodium, respectively (for both direct and indirect procedures). The spectrophotometric and the atomic absorption spectrometric procedures hold well their accuracy and precision when applied to the analysis of cefotaxime sodium and cefuroxime sodium dosage forms.

Utility of certain π-acceptors for the spectrophotometric determination of perindopril

Simple, rapid, accurate and sensitive spectrophotometric methods are described for the determination of perindopril. The methods are based on the reaction of this drug as n-electron donor with 2,3-dichloro-5,6-dicyano-p-benzoquinone(DDQ)-7,7,8,8- tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), chloranil (CL) and p-chloranilic acid (p-CA) as pi-acceptors to give highly coloured complex species. The coloured products are measured spectrophotometrically at 588, 843, 419, 550 and 520 nm for DDQ, TCNQ, TCNE, CL and p-CA, respectively, optimization of different experimental conditions is described. Beers law is obeyed in the range of 20-200 micrograms ml-1 and colours were produced in non-aqueous media and were stable for at least 1 h. Application of the suggested methods to perindopril tablets are presented.

Potentiometric determination of famotidine in pharmaceutical formulations.

Two new potentiometric methods for determination of famotidine in pure form and in its pharmaceutical tablet form are developed. In the first method, the construction of plasticised poly(vinyl chloride) (PVC) matrix-type famotidine ion-selective membrane electrode and its use in the potentiometric determination of famotidine in pharmaceutical preparations are described. It is based on the use of the ion-associate species, formed by famotidine cation and tetraphenyl borate (TPB) counterion. The electrode exhibited a linear response for 1 x 10(-3)-1 x 10(-5) M of famotidine solutions over the pH range 1-5 with an average recovery of 99.26% and mean standard deviation of 1.12%. Common organic and inorganic cations showed negligible interference. In the second method, the conditions for the oxidimetric titration of famotidine have been studied. The method depends on using lead(IV) acetate for oxidation of the thioether contained in famotidine. The titration takes place in presence of catalytic quantities of potassium bromide (KBr). Direct potentiometric determination of 1.75 x 10(-2) M famotidine solution showed an average recovery of 100.51% with a mean standard deviation of 1.26%. The two methods have been applied successfully to commercial tablet. The results obtained reveal good percentage recoveries, which are in good agreement with those obtained by the official methods.

Determination of sulphacetamide, sulphadimidine or sulphathiourea in the presence of their degradation products using first derivative spectrophotometry

A method is presented for the determination of sulphacetamide sodium, sulphadimidine and sulphathiourea in the presence of their acid-induced degradation products using first derivative spectrophotometry. By measuring the absolute value of the first derivative curves at the zero contribution of the corresponding degradation products, the concentration of the intact drug can be calculated directly without interference of the degradation product. The validity of the method was confirmed using synthetic mixtures of the intact drugs with their degradation products.

Spectrscopic and Conductometric Analysis of Gabapentin

Four simple, sensitive and reproducible methods were developed for the determination of gabapentin (GPT) in pure form and in pharmaceutical preparations. Methods A and B are based on the reaction of cupric chloride with gabapentin to form stable complex, which could be measured spectrophotometrically atmax 246 nm (method A) or by using conductometric technique (method B). While method C and D depends on the formation of ion pair complex between the studied drug and bromothymol blue, bromocresol green respectively this was extractable with methylene chloride. The concentration ranges were 40-95 µg mL -1 , 1-15 mg, 100-800 and 10-150 µg mL -1 for methods A, B, C and D respectively .The optimization of various experimental conditions were described .The results obtained showed good recoveries, Ringbom optimum concentration ranges were calculated, in addition to molar absorptivity and sandells sensitivity, detection and quantification limits. The methods were successfully applied to the determination of GPT in bulk and pharmaceutical preparations. The results were favorably comparable with the official method. The molar combining ratio for methods (A-B) was found to be (2:1) (drug: reagent) while for method (C-D) it was found to be (1:1).

Kinetic Spectrophotometric Determination of Betahistine Dihydrochloride and Etilefrine Hydrochloride in Pharmaceutical Formulation

The importance of betahistine dihydrochloride as an anti-vertigo medicine and of etilefrine hydrochloride in the management of hypotension necessitates the development of a simple, sensitive and inexpensive technique for their analysis. This study reports the development of an accurate, feasible kinetic technique for their determination. It is based on the reaction of the cited drugs with 4-chloro-7-nitrobenzofurazan (NBD–Cl) in presence of 0.05 M disodium hydrogen phosphate. The absorbance was measured at 496, and 503 nm for betahistine dihydrochloride and etilefrine hydrochloride respectively, at a fixed time of 30 minutes on thermostated water bath at 90°C. The absorbance concentration plots were rectilinear over the range 0.25–7 and 3–13 μg/ml for betahistine dihydrochloride and etilefrine hydrochloride, respectively. The method has been applied successfully to commercial tablet dosage form and can be further applied for their determination on a large scale in quality control laboratories, or in small laboratories. The obtained results statistically agreed with those obtained by official titrimetric methods. The determination of the studied drugs by the fixed concentration and rate constant methods is feasible with the calibration equations obtained, but the fixed time method proves to be more applicable.