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.     

A direct titrimetric method for the microdetermination of some phenothiazine derivatives in pharmaceutical preparations

A micro method has been developed for the determination of some phenothiazine derivatives in pure form and in pharmaceutical preparations, 1-5 mg of sample being titrated directly with 0.02M N-bromosuccinimide, with Methyl Red as indicator. The error does not exceed +/-1%.     

Raman spectra of phenothiazine and some pharmaceutical derivatives

The laser-Raman spectra of several phenothiazines in the region 600-1600 cm(-1) are reported. The major bands are assigned to ring modes or to vibrations of the alkyl side-chains.     

Extractive spectrophotometric determination of some fluoroquinolone derivatives in pure and dosage forms

Two simple and sensitive extractive spectrophotometric methods for the determination of some fluoroquinolone derivatives (norfloxacin, NRF; ciprofloxacin, CPF; ofloxacin, OFL; and enrofloxacin, ERF) with Supracene Violet 3B (SV 3B, method A) and tropaeolin 000 (TP 000, method B) are described. The methods are based on the formation of ion-association complexes of fluoroquinolones with these dyes, which are extracted into chloroform and have absorption maxima at 575 nm (SV 3B) and 485 nm (TP 000). The methods obey Beer's law and the precision and accuracy of the methods were checked by UV reference methods. The detection limits were 5.0 mug/ml for NRF and 2.5 mug/ml for CPF in method A and 2.5 mug/ml for OFL and ERF in methods A and B.     

Spectrophotometric determinations of some phenothiazine drugs

A rapid and sensitive spectrophotometric method has been developed for the quantitative determination of some phenothiazine derivatives as the pure substances and in different dosage forms. The method is based on the formation of red coloured products with 1% iodic acid in sulphuric or phosphoric acid medium. The reaction involves oxidation of the phenothiazine nucleus into a semiquinonoid radical. The optimum reaction conditions and other analytical parameters are evaluated. The influence of the substrates commonly employed as excipients with phenothiazine drugs has been studied. Statistical comparison of the results with those of an official method shows excellent agreement and indicates no significant difference in precision.     

A sensitive and selective spectrophotometric estimation of catechol derivatives in pharmaceutical preparations

A sensitive and simple spectrophotometric method for the estimation of catechol and its derivatives like dopamine hydrochloride (DPH), levodopa (LDP), methyldopa (MDP) and adrenaline hydrochloride (ADH) in both pure form and in pharmaceutical formulation, is described. The method is based on the interaction of diazotised sulphanilamide (DSA) with catechol derivatives in the presence of molybdate ions in acidic medium. Absorbance of the resulting red coloured product is measured at 490 nm for pyrocatechol (PCL) and at 500 nm for other catechol derivatives. The colour reaction is stable for 24–30 h. Under optimal conditions, Beer's Law range for pyrocatechol was found to be between 0.04 and 2.4 (R.S.D.=0.78%), for DPH was 0.02–2.8 (R.S.D.=0.98%) for LDP was 0.1–2.8 (R.S.D.=1.21%) for MDP was 0.5–7 (R.S.D.=1.41%) and for ADH was 0.5–7 (R.S.D.=1.58%). The method is highly reproducible and specific for these selected catechol derivatives. The common excipients used as additives do not interfere in the proposed method. Analytical data for the determination of the pure compound is presented together with the application of the proposed method to the analysis of some pharmaceutical formulations. The results compare favourably with those of official and reported methods.     

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.     

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.     

Simultaneous spectrophotometric determination of fat-soluble vitamins in multivitamin pharmaceutical preparations

A spectrophotometric method is proposed for the simultaneous determination of vitamins A, D and E in multivitamin pharmaceutical preparations. This is based on multiple linear regression. Most vitamins are directly extracted from the preparations into n-hexane. Microen-capsulated vitamin A preparations require pretreatment of de-encapsulation before the vitamin is extracted. The wavelength range to be used for each preparation and the optimum spectral mode (absorbance or first-derivative) has been chosen in order to assure correct quantitation and avoid interferences from other absorbing species also extracted by n-hexane. The results obtained were validated by simultaneous HPLC analyses for accuracy and precision.     

Sequential injection spectrophotometric determination of phenylephrine hydrochloride in pharmaceutical preparations

A fully automated sequential injection spectrophotometric method for the determination of phenylephrine hydrochloride in pharmaceutical preparations is reported. The method is based on the condensation reaction of the analyte with 4-aminoantipyrine in the presence of potassium ferricyanide. The absorbance of the condensation product was monitored at 503 nm. A linear relationship between the relative peak height and concentration was obtained in the range 0.5-17.5 mg l⁻¹. The detection limit (as 3σ value) was 0.09 mg l⁻¹ and repeatability was 0.8 and 0.6% at 2.5 and 5 mg l⁻¹, respectively. Results obtained by this method agreed very well with those obtained by the AOAC official method.     

Indirect spectrophotometric determination of benzylpenicillin and cloxacillin in pharmaceutical preparations

An indirect spectrophotometric method for the determination of benzylpenicillin and cloxacillin is based on extraction of iodine produced by reduction of potassium iodate in acidic medium, where hydrolytic cleavage of a -lactam is achieved with sodium hydroxide. Beer's law is obeyed within the concentration ranges 0.04–0.8 mg ml^–1 benzylpenicillin and 0.02–0.5 mg ml^–1 cloxacillin. The precision, accuracy of the method and the effect of foreign substances were studied. The results have been statistically compared with those using the ammonium vanadate method. An oxidation mechanism is proposed.     

Visible spectrophotometric and first-derivative UV spectrophotometric determination of rifampicin and isoniazid in pharmaceutical preparations

Two methods are described for the determination of rifampicin and isoniazid in mixtures by visible spectrophotometry and first-derivative ultraviolet spectrophotometry. The absorbance at 475 nm in buffer solution pH 7.4 was employed to determine rifampicin after applying the three-point correction technique between 420 and 520 nm, while the amplitude of the first-derivative spectrophotometric spectrum at 257 nm in HCl 0.012 M was selected for the determination of isoniazid. The methods are rapid, simple and do not require any separation step. The recovery average was 99.03% for rifampicin and 100.01% for isoniazid. The methods were applied to determine the two compounds in commercial capsules and compared with the official method of the USP XXIII with good agreement between the results.     

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.     

Simultaneous spectrophotometric determination of mefenamic acid and paracetamol in pharmaceutical preparations

A spectrophotometric procedure for the simultaneous determination of mefenamic acid and paracetamol in a mixture is described. Using 0.01 M methanolic hydrochloric acid as solvent, the absorbance of the mixture is measured at 248, 279 and 351 nm. The concentration of each component can be calculated by solving two equations using two wavelengths, either 248 and 279 nm or 248 and 351 nm.