Utility of some pi-acceptors for spectrophotometric determination of gatifloxacin in pure form and in pharmaceutical preparations

Four simple, quick and sensitive methods are described for the spectrophotometric determination of gatifloxacin. The methods are based on the reaction of gatifloxacin as n-electron donor with 7,7,8,8-tetracyanoquinodimethane (TCNQ); 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ); chloranilic acid (CLA) and p-chloranil (CL) as pi-acceptors to give highly colored complex species. The colored products are quantitated spectrophotometrically at 460, 841, 530 and 545 nm for DDQ, TCNQ, CLA and CL, respectively. Optimization of the different experimental conditions is described. Beer's law is obeyed in the concentration ranges 5-60, 1.5-18, 30-360 and 20-240 microg ml(-1) of gatifloxacin, but for more accurate analysis, Ringbom optimum concentration range was found to be 7.5-55, 3-16, 35-350 and 25-230 microg ml(-1) of gatifloxacin for DDQ, TCNQ, CLA and CL, respectively. The limits of detection and quantification were calculated and the relative standard deviations for different concentrations of gatifloxacin using various acceptors were <1.28%. The association constants of 1 : 1 complexes and standard free energy changes using Benesi-Hildebrand plots were studied. The proposed methods were successfully applied to the determination of gatifloxacin in pharmaceutical dosage forms without interference from common additives encountered.     

Use of pi-acceptors for spectrophotometric determination of dicyclomine hydrochloride

Simple, rapid, accurate, and sensitive spectrophotometric methods are described for the determination of dicyclomine hydrochloride. The methods are based on the reaction of this drug as an n-electron donor with 2,3-dichloro-5,6-dicyano-p-benzoqunione (DDQ), p-chloranilic acid (p-CA), and chloranil (CL) as pi-acceptors to give highly colored complex species. The colored products are measured spectrophotometrically at 456, 530, and 650 nm for DDQ, p-CA, and CL, respectively. Optimization of the different experimental conditions were studied. Beer's law was obeyed in concentration ranges of 20-100, 50-250, and 80-600 microg/mL for DDQ, pCA, and CL, respectively. Colored complexes are produced in organic solvents and are stable for at least 1 h. The methods were applied to Spasmorest antispasmotic tablets and ampoules with good accuracy and precision.     

Utility of NBD-Cl for the spectrophotometric determination of some skeletal muscle relaxant and antihistaminic drugs

A simple, accurate, precise and sensitive colorimetric method for the determination of some skeletal muscle relaxant drugs, namely orphenadrine citrate (I), baclofen (II), antihistaminic drugs as acrivastine (III) and fexofenadine hydrochloride (IV) is described. This method is based on the formation of charge transfer complex with 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) in non-aqueous medium. The orange color products were measured at 472, 465, 475 and 469 nm for drugs I, II, III and IV, respectively. The optimization of various experimental conditions was described. Beer's Law was obeyed in the range (2.5-17.5), (5-70), (2.5-25) and (10-50)microg/ml for drugs I, II, III and IV, respectively. The molar absorptivity (epsilon), sandell sensitivity, detection((LOD)) and quantitation limits((LOQ)) are calculated. The procedure was favorably applied for determination of certain pharmaceutical dosage forms containing the studied drugs. The obtained results were compared with the official and reported methods. There were no significant differences between proposed, reported and the official methods.     

Oxidized haematoxylin,a new reagent for the spectrophotometric determination of penicillins and cephalosporins

Haematoxylin—Chloramine-T in phosphate buffer (pH 7.0) is proposed as a new reagent for spectrophotometric determination of penicillins and cephalosporins in pure samples and pharmaceutical preparations. The method is based on acid hydrolysis of penicillins and cephalosporins with 5M HCl and subsequent treatment with oxidized haematoxylin. The resulting colour exhibits maximum absorption at 555 nm.     

Utility of the ion-pair formation for spectrophotometric determination of terfenadine in pure form and in some pharmaceutical formulations

A spectrophotometric procedure for the determination of terfenadine and a number of its pharmaceutical preparations has been developed that offers advantages of simplicity, rapidity, sensitivity and stability indication over the official USP (1995) method. The proposed method is based on the formation of ion-pairs by the reaction of terfenadine with some chromotropic acid mono- and bis-azo dyes. Different variables affecting the ion-pair formation were studied and optimized. At the maximum absorption of 557, 521, 592 and 543 nm, Beer's law is obeyed in the range 0.2–18.6, 0.2–16.4, 0.2–25.0 and 0.2–22.2 g ml^–1 on using reagents I, II, III and IV, respectively. The stoichiometric ratio and stability of each ion-pair were estimated and the mechanism of the reaction is discussed. The molar absorptivity and Sandell sensitivity of the produced ion-pairs were calculated in addition to Ringbom optimum concentration ranges. Statistical treatment of the experimental results indicates that the procedures are precise and accurate. Excipients used as additives in pharmaceutical formulations did not interfere in the proposed procedures. The reliability of the methods was established by parallel determination against the official USP method. The procedures described were successfully applied to the determination of the bulk drug and its pharmaceutical formulations by applying the standard addition technique.     

Spectrophotometric determination of some penicillins with ammonium vanadate

A spectrophotometric method for determining some penicillins has been developed. A known volume of the penicillin solution-in phosphate buffer of pH 6.8 is boiled with ammonium vanadate solution-in sulphuric acid medium-for 10 min and the absorbance of the colour formed is measured at 750 nm. The excess of vanadate can also be determined volumetrically. The method has been successfully applied for the determination of penicillin G sodium, phenoxymethyl penicillin, ampicillin sodium, phenethicillin potassium, cloxacillin sodium and methicillin sodium. The procedure is also used for analysing some pharmaceutical preparations of these drugs, e.g., injections. The results obtained are in agreement with those of the B P 1973 methods.     

Some spectrophotometric methods for determination of certain antipyretic and antirheumatic drugs

Heating paracetamol in strongly alkaline medium with 4-nitrosoantipyrine gives a red colour with maximum absorption at 515 nm. Mefenamic and flufenamic acids can be determined colorimetrically after extraction as ion-pairs with Methylene Blue.     

The determination of some selected penicillins by enzymatic enthalpimetry

An enzymatic, enthalpimetric procedure is described for the determination of penicillin G, ampicillin sodium or phenoxymethylpenicillin in pure and dosage forms. The technique employed allows up to 20 assays with the same reagent solution. Enthalpy assignments are presented along with error (range) and precision data. The lower limit of determination is about 10^-3 mol dm^-3.     

Oxidative coupling for the spectrophotometric determination of certain cephalosporins and acetaminophen in drug formulations

A spectrophotometric method for the determination of some cephalosporins and acetaminophen is described. The method is based on the hydrolysis of the cephalosporin in sodium hydroxide solution to produce the sulphide ion and the conversion of the sulphide with the p-phenylenediamine to form a violet colour. Acetaminophen is hydrolysed in sulphuric solution and the resulting p-aminophenol is oxidized with sulphide ion in the presence of iron(III) to form a red product. The method has been successfully applied to the assay of some cephalosporins and acetaminophen in drug formulations.     

Kinetic spectrophotometric determination of certain cephalosporins using oxidized quercetin reagent

A simple, precise and accurate kinetic spectrophotometric method for determination of cefoperazone sodium, cefazolin sodium and ceftriaxone sodium in bulk and in pharmaceutical formulations has been developed. The method is based upon a kinetic investigation of the reaction of the drug with oxidized quercetin reagent at room temperature for a fixed time of 30 min. The decrease in absorbance after the addition of the drug was measured at 510 nm. The absorbance concentration plot was rectilinear over the range 80–400 μg mL⁻¹ for all studied drugs. The concentration of the studied drugs was calculated using the corresponding calibration equation for the fixed time method. The determination of the studied drugs by initial rate, variable time and rate-constant methods was feasible with the calibration equations obtained but the fixed time method has been found to be more applicable. The analytical performance of the method, in terms of accuracy and precision, was statistically validated; the results were satisfactory. The method has been successfully applied to the determination of the studied drugs in commercial pharmaceutical formulations. Statistical comparison of the results with a well established reported method showed excellent agreement and proved that there is no significant difference in the accuracy and precision.     

Utility of diphenylamine and N-bromosuccinimide for colorimetric determination of certain phenothiazine drugs

A sensitive colorimetric method for the quantitative estimation of 11 phenothiazine drugs was developed. The method was based on the interaction of phenothiazine compounds with diphenylamine in presence of N-bromosuccinimide and sulfuric acid. Most of studied phenothiazines yielded bluish green products with two absorption maxima, one in the range of 392-396 nm with higher molar absorptivity and the other in the range of 770-780 nm with lower molar absorptivity. Phenothiazine base, mepazine HCl and pericyazine yielded blue products with only one maximum at 655, 775 and 778 nm, respectively. The color was stable for at least 1 h. The reproducibility and recovery of the method were excellent. The method was applied successfully to the determination of some commercially available phenothiazines in different dosage forms. Results were comparable to those obtained by official and reported methods.     

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%.     

The use of chloranil for spectrophotometric determination of some tranquillizers and antidepressants

Chlorpromazine hydrochloride, promethazine hydrochloride, promazine hydrochloride, perphenazine, thioridazine hydrochloride, chlorprothexine, opipramol hydrochloride, amitriptyline hydrochloride, imipramine hydrochloride and hydroxyzine hydrochloride are estimated in their pure state and in pharmaceutical formulations by means of the reaction of the free bases with chloranil in dioxan-ethanol medium to give a coloured product with maximal absorbance at 550 nm. The method is precise, accurate and specific and recommended for routine analysis for the drugs mentioned.     

Phosphomolybdic acid as a reagent for the spectrophotometric determination of certain phenothiazine derivatives of pharmaceutical products

Phosphomolybdic acid is used as reagent for colorimetric determination of phenothiazine derivatives in various pharmaceutical products. The reagent oxidizes the derivative to a cationic free radical, with which it then forms a coloured salt. The method is simple and rapid. A preliminary extraction is necessary if certain reductants (sulphite or ascorbic acid) are present as stabilizers of the pharmaceuticals, as otherwise they reduce the reagent to phosphomolybdenum blue.     

Application of promethazine hydrochloride as a chromogenic reagent for the spectrophotometric determination of certain sulphonamide drugs

Summary The oxidative coupling reaction of promethazine · HCl with primary aromatic amines was applied to the determination of seven pharmaceutical sulphonamides. A mixture of an acidic solution (3.5% acetic acid) of the sulphonamide and the chromogenic reagent was treated with hypochloriteion. The wavelength of maximum absorption is 610 nm, the molar absorptivities range from 1.57×10⁴ to 1.89×10⁴ l mole^–1 cm^–1 and Sandell sensitivities range from 0.00972 to 0.0136 g cm^–2. A linear correlation was found between absorbance at max and concentration. The procedures developed for bulk sulpha drugs and some of their pharmaceutical preparations are rapid, accurate, precise and comparable to the Bratton-Marshall procedure.     

Multiwavelength spectrophotometric determination of acidity constants of some azo dyes

A multiwavelength spectrophotometric titration method was applied to study the acidity constants of some azo dyes in water. The UV-vis absorption spectra of azo dye solutions were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants, spectral profiles, concentration diagrams and also the number of components have been calculated. The quantitative effects of the substituents on the acidity of the studied azo dyes were investigated by the linear free energy relationship (LFER) using Hammet sigma constant (sigma) and field and resonance effects of Kamlet and Taft (f and Re, respectively).     

Extractive spectrophotometric determination of some phenothiazine derivatives in pharmaceutical preparations

A simple, accurate, rapid and sensitive spectrophotometric method has been developed for the assay of six phenothiazine derivatives in bulk drug and their pharmaceutical preparations. The method is based on ion-pair complex reaction of phenothiazines with bromocresol green in aqueous acidic buffer. The chromogen, being extractable with chloroform, could be measured quantitatively at 420 nm. All variables were studied in order to optimize the reaction conditions. The proposed method has been successfully applied to the analysis of the bulk drugs and their dosage forms, tablets and injections. No interference was observed from common pharmaceutical adjuvants. Statistical comparison of the results with those of an official method shows excellent agreement and indicates no significant difference in precision.     

The spectrophotometric and heterometric determination of some alkaloids as cobaltothiocyanates

Small amounts of papaverine (about 3 mg in 15 ml solution) can be determined heterometrically in the presence of thiocyanate by titration with cobaltous solution. A strong electrolyte (Na₂SO₄) must be added to obtain a clear endpoint. The titration can be carried out in the presence of large amounts (97%) of quinine and ephedrine. The titration takes 2–3 min and the error rarely exceeds 1%.Papaverine, quinine, and ephedrine can be determined individually by spectrophotometry as their cobaltothiocyanates, which are extracted in 30% cyclohexanone in carbon tetrachloride, and the optical density measured at 625 nm. The method is reproducible at milligram levels with a standard deviation of ±0.3% for papaverine and quinine and = 0.5% for ephedrine.     

Extractive spectrophotometric determination of some anti-inflammatory agents with methylene violet

A fairly sensitive spectrophotometric method for the determination of ibuprofen, ketoprofen, piroxicam, diclofenac sodium, mefenamic acid or enfenamic acid in bulk samples and pharmaceutical preparations is described, based on the formation of a chloroform-soluble, coloured ion-association complex between the drug and Methylene Violet at pH 7.6.