Simultaneous determination of ascorbic acid and acetylsalicylic acid in pharmaceutical formulations.

A direct, simple, and practical first-derivative spectrophotometric method is described for simultaneous determination of ascorbic acid and acetylsalicylic acid. The effects of the solvent, excipients, and spectral variables on the analytical signal were investigated. The drugs were determined simultaneously with a 0.01 M methanolic hydrochloric acid solution as the solvent, and the signals were evaluated directly by using the zero-crossing method at 245.0 and 256.0 nm for acetylsalicylic acid and ascorbic acid, respectively. The method allows the simultaneous determinations of acetylsalicylic acid and ascorbic acid in the ranges of 6.6 x 10(-6) to 1.5 x 10(-4)M and 3.4 x 10(-6) to 2.0 x 10(-4)M, respectively, with standard deviation of <2.0%. The proposed method was applied to determinations of these drugs in tablets.

Simultaneous determination of chlordiazepoxide and clidinium bromide in pharmaceutical formulations by derivative spectrophotometry.

A direct and simple first derivative spectrophotometric method has been developed for the simultaneous determination of clidinium bromide and chlordiazepoxide in pharmaceutical formulations. Acetonitrile was used as solvent for extracting the drugs from the formulations and subsequently the samples were evaluated directly by derivative spectrophotometry. Simultaneous determination of the drugs can be carried out using the zero-crossing method for clidinium bromide at 220.8 nm and the graphical method for chlordiazepoxide at 283.6 nm. The calibration graphs were linear in the ranges from 0.983 to 21.62 mg/l of clidinium bromide and from 0. 740 to 12.0 mg/l of chlordiazepoxide. The ingredients commonly found in commercial pharmaceutical formulations do not interfere. The proposed method was applied to the determination of these drugs in tablets.

Simultaneous determination of iron and ruthenium as ternary complexes by extractive second derivative spectrophotometry.

A highly sensitive and selective second derivative spectrophotometric method has been developed for the determination of ruthenium and iron in mixtures. The method is based on the formation of the binary complexes of iron and ruthenium with 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline) in the presence of ethyleneglycol. These complexes are formed at pH 4.0-6.0 upon heating at 90 degrees C for 60 min. The ternary perchlorate complexes are then separated by liquid-liquid extraction. The extracts were evaluated directly by derivative spectrophotometric measurement, using the zero-crossing approach for determination of both analytes. Ruthenium and iron were thus determined in the ranges 9.6-450 and 16.3-280 ng/ml, respectively, in the presence of one another. The detection limits achieved (3sigma) were found to be 2.9 ng/ml of ruthenium and 4.9 ng/ml of iron. The relative standard deviations were in all instances less than 1.5%. The proposed method was applied to the determination of both analytes in synthetic mixtures.

Flow injection photometric determination of zinc and copper with zincon based on the variation of the stability of the complexes with pH.

A flow injection photometric method for the sequential determination of zinc and copper in mixtures was developed based on the variation of the stability of the chromogenic complexes between the analytes and the reagent zincon with pH. At pH 5.0 only the Cu-zincon complex exists, whereas at pH 9.0 the copper and zinc chelates co-exist. A three-channel manifold was implemented containing two alternating buffer streams (pH 5 and 9) which permit the colored reaction products to be formed sequentially at both pH values, and consequently the mixtures can be resolved. A continuous preconcentration unit (Chelex-100) was used in order to increase the sensitivity of the method, thus allowing the analysis of water samples in which the analytes are present at the ng ml-1 level. On the other hand, preconcentration was not required when the analytes were determined in brass. Under the optimum conditions and using a preconcentration time of 2 min, the detection limits (3 sigma) were found to be 0.35 and 0.80 ng ml-1 for zinc and copper, respectively. The repeatability of the method, expressed as the RSD, was in all instances less than 3.1%. Considering the sequential determination of both species, a sampling rate of 70 h-1 was obtained if preconcentration of the samples was not required.

Simultaneous determination of copper and iron by second derivative spectrophotometry using mixtures of ligands.

A highly sensitive and selective second derivative spectrophotometric method has been developed for the determination of copper and iron in mixtures. The method is based on the separation of the analytes by liquid-liquid extraction as picrate ion pairs. Iron-picrate, reacts in the organic phase of DCE with 5-phenyl-3-(4-phenyl-2-pyridinyl)-1,2,4-triazine (PPT). Similarly the copper-picrate reacts with 2,9-dimethyl-4,7-diphenyl-1,10-phenantroline (bathocuproine). The extracts were evaluated directly by derivative spectrophotometric measurement, using the zero-crossing approach for determination of copper and graphic method for iron. Iron and copper were thus determined in the ranges 8-120 ng ml(-1) and 8-125 ng ml(-1), respectively, in the presence of one another. The detection limits achieved (3sigma) were 2.9 ng ml(-1) of iron and 2.8 ng ml(-1) of copper. The relative standard deviations were in all instances less than 2.1%. The proposed method was applied to the determination of both analytes in river and tap water and the results were consistent with those provided by the AAS standard method.

Polarographic behaviour and determination of ranitidine in pharmaceutical formulations and urine.

A polarographic method for the determination of ranitidine is described, based on the reduction of the nitro group at a dropping-mercury electrode. The proposed method permits the drug to be determined, without any prior separation or extraction, in pharmaceutical formulations and urine at levels at which the unchanged drug is excreted. The current is diffusion controlled and proportional to concentration from 3.58 x 10(-3) to 1.50 mmol l-1. The detection limit is 1.07 x 10(-3) mmol l-1. The reduction process was studied at different pH values and a reduction mechanism is proposed in which the importance of the homogeneous chemical reactions associated with the electron-transfer steps are indicated.

Determination of trace amounts of cobalt by solvent extraction--second derivative spectrophotometry.

A sensitive derivative spectrophotometric method is described for the determination of microamounts of cobalt based on the integration of liquid-liquid separation and reaction, in dichloroethane, of the analyte with 3-(4-phenyl-2-pyridinyl)-5-phenyl-1,2,4-triazine (PPT) and 2,4,6-trinitro-phenol (picric acid). Cobalt was thus determined in the range 7.2-500 ng/ml. The method has a high selectivity with a detection limit of 2.2 ng/ml. The relative standard deviations were 3.2 and 1.5% for 20 and 100 ng/ml cobalt, respectively. The proposed method was applied to the determination of the analyte in vitamins.

Spectrophotometric and derivative spectrophotometric determination of iron by extraction of the iron(II)-TPYZ-picrate ion-association complex.

A solvent extraction-spectrophotometric determination of microamounts of iron has been developed, based on the formation of an ion-association complex of iron(II) with 2,4,6-tris(2'-pyridyl)-1,3,5-triazine as primary ligand and picrate as counter-ion, which is extracted into 1,2-dichloroethane. The complex is formed at pH 4.0-7.0 and the iron concentration can be determined by measuring the absorbance directly in the organic phase. The apparent molar absorptivity is 2.2 x 10(5) l.mole(-1).cm(-1). As the method is practically free from interferences it was applied to the determination of iron in different biological and inorganic samples. Although the proposed method is very sensitive it can be further sensitized by employing the derivative spectrophotometric technique.