Spectrophotometric methods for the determination of ritodrine hydrochloride and its application to pharmaceutical preparations

Two simple and sensitive spectrophotometric methods are described for the determination of ritodrine hydrochloride (RTH) in both pure and dosage forms. The methods are based on the interaction of diazotised p-nitroaniline (DPNA) and sulphanilic acid (DSNA) with RTH in an alkaline medium. The resulting azo dyes are measured at 480 nm (for the DPNA method) and at 440 nm (for the DSNA method) and are stable for more than 1 h. The optimum reaction conditions and other analytical parameters are evaluated. A study of the effect of commonly associated excipients and additives do not interfere with the determinations. Statistical analysis of results indicates that the methods are precise and accurate.     

Spectrophotometric determination of codeine in pharmaceutical preparations

A spectrophotometric method for determination of codeine is described. The method is based on the reaction of codeine with bromocresol green. The yellow complex formed was extracted with chloroform at pH 3.8. The solution of complex in chloroform showed maximum absorbance at 418 nm. The complex was stable up to 10 days and obeyed Beer's law over the concentration ranges of 3–12 μg/ml. The ratio of codeine to bromocresol green was 1:1. Excipients, coloring matter, flavoring agents and some other compounds likely to be present in the codeine-containing preparation did not interfere in the determination. The interferences can be eliminated by preliminary TLC separation.     

Spectrophotometric determination of pefloxacin in pharmaceutical preparations

It has been established that the antibiotic pefloxacin (Abaktal) methane-sulphonate reacts with Fe(III) at pH 1.00–8.00 to form a water-soluble complex with maximum absorbance at 360 nm. The composition of the complex, determined spectrophotometrically by the application of Job's, molar-ratio and Bent—French's methods, was pefloxacin: Fe(III) = 1:1 (pH = 2.50; λ = 360 nm; μ = 0.1 M). The relative stability constant, obtained by the methods of Sommer and Asmus was 10^5.02 (pH = 2.50; λ = 360 nm; μ = 0.1 M). The molar absorptivity of the complex at 360 nm was found to be 4.8 × 10³ l mol⁻¹ cm⁻¹, Beer's law was followed for pefloxacin concentrations of 2.15–85.88 μg ml⁻¹. The lower sensitivity limit of the method was 2.15 μg ml⁻¹. The relative standard deviation (n = 10) was 0.57–1.07%. The method can be applied to the rapid and simple determination of pefloxacin in aqueous solutions and tablets.     

Spectrophotometric determination of oxytetracycline in pharmaceutical preparations using sodium molybdate as analytical reagent

A spectrophotometric method is proposed for the determination of oxytetracycline in pharmaceutical preparations. The method is based on the measurement of the absorbance of the molybdate—oxytetracycline complex at 404 nm (pH 5.50; μ = 0.1 M; 20°C). The composition of the complex (1:1) was determined by the application of the spectrophotometric methods of Job and Bent—French (pH 5.50; λ = 390 nm; μ = 0.1 M). The relative stability constant (K′ = 10^4.6) of the complex was obtained by the methods of Sommer and Nash (pH 5.50; λ = 390 nm; μ = 0.1 M; 20°C). The molar absorptivity of the complex was 9.5 × 10³ l mol⁻¹ cm⁻¹. Beer's law was obeyed over the concentration range 2.48–34.78 μg ml⁻¹. The relative standard deviation RSD (n = 10) was 0.27–0.39%. The method proposed can be applied to the assay of oxytetracycline in capsules. The detection limit of oxytetracycline is 2.5 μg ml⁻¹.     

Spectrophotometric and spectrofluorimetric determination of atomoxetine in pharmaceutical preparations

Visible spectrophotometric and spectrofluorimetric methods were developed for the determination of atomoxetine in pharmaceutical preparations. The spectrophotometric method was based on a nucleophilic substitution reaction of atomoxetine with 1,2-naphthoquinone-4-sulphonate (NQS) in an alkaline medium to form an orange-colored product. The absorbance-concentration plot is rectilinear over the range 5-40 microg mL(-1). The limits of detection and quantification were calculated to be 0.02 microg mL(-1) and 0.06 microg mL(-1), respectively. The spectrofluorimetric method was based on the derivatization reaction of 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) with atomoxetine to produce a fluorescent derivative. The formed highly fluorescent derivative that was measured at 462 nm after excitation at 533 nm. The fluorescence-concentration plot is rectilinear over the range 10-500 ng mL(-1). The limits of detection and quantification were calculated to be 0.19 ng mL(-1) and 0.57 ng mL(-1). The analytical performance of both methods was fully validated, and the results were satisfactory. The methods have been successfully applied for the determination of the studied drug in capsules and the results obtained ware in good agreement with those obtained by the reference method.     

Spectrophotometric determination of metronidazole and secnidazole in pharmaceutical preparations

A rapid and sensitive spectrophotometric method is proposed for determination of metronidazole and secnidazole. The method depends on the reduction of metronidazole and secnidazole molecule with zinc dust and hydrochloric acid flowed by diazotization and coupling with 8-quinolinol to give red colored chromogens easily measured spectrophotometrically which has λ_max = 500 nm. The experimental conditions were optimized and Berr's law was obeyed over the applicable concentration ranges both techniques were applied successfully to a wide variety of pharmaceutical preparations.     

Spectrophotometric determination of metronidazole and tinidazole in pharmaceutical preparations

Sensitive and simple spectrophotometric methods for the determination of metronidazole (MNZ) and tinidazole (TNZ) in either pure form or in its pharmaceutical formulations are described. The first method is based on the interaction of 3-methylbenzothiazolin-2-one hydrazone (MBTH) with MNZ/TNZ (reduced drug) in presence of copper sulphate and pyridine in acidic medium. The resulting yellowish orange products have lambda(max) of 500 and 490 nm, respectively, for MNZ and TNZ and are stable for about 4 h. The second method describes the reaction between reduced diazotised drugs with N-(1-naphthyl)ethylenediamine dihydrochloride (NEDA) in neutral medium to yield pink products which have lambda(max) of 520 and 505 nm, respectively, for MNZ and TNZ, respectively. The products are stable for more than 24 h. Common excipients used as additives in pharmaceutical preparations do not interfere in the proposed method. Both the methods are highly reproducible and have been applied to a wide variety of pharmaceutical preparations and the results compare favourably with those of official methods.     

Spectrophotometric methods for the determination of gemifloxacin in pharmaceutical formulations

This paper describes two simple spectrophotometric methods for the determination of the antibiotic gemifloxacin mesylate (GFX) in pharmaceutical formulations. The first (A) is an indirect method in which oxidation of the drug with a known excess of cerium (IV) sulphate is followed by determination of the residual oxidant by adding excess methyl orange and measuring residual dye at 507 nm. The second (B) is a derivatisation method involving reaction of GFX with 1,2-naphthoquinone-4-sulphonate (NQS) in alkaline medium (pH 11) to form an orange-coloured product exhibiting maximum absorption (λ_max) at 411 nm. The methods were linear in the concentration ranges 2–9 and 5–30 μg/mL for methods A and B, respectively, with intra-day precision (as RSD) <1.5% for both. When applied to the determination of GFX in pharmaceutical tablets, the results were in good agreement with those obtained by capillary electrophoresis. The two methods are useful for routine analysis of GFX in quality control laboratories.     

Chemiluminescence analysis of menadione sodium bisulfite and analgin in pharmaceutical preparations and biological fluids

A novel chemiluminescence (CL) flow system for two sulfite-containing drugs, namely, menadione sodium bisulfite (MSB) and analgin is described. It is based on the weak chemiluminescence induced by the oxidation of sulfite group in drugs with dissolved oxygen in the presence of acidic Rh6G. Tween 80 surfactant micelles showed a strong enhancement effect on this weak chemiluminescence. For MSB analysis, online conversion of MSB in alkaline medium into sodium bisulfite was necessary, whereas analgin could be determined directly. The proposed method allowed the measurement of 0.05-50 microg/ml(-1) MSB and 0.05-10 microg/ml(-1) analgin. The limits of detection (3sigma) were 0.01 microg/ml(-1) MSB and 0.003 microg/ml(-1) analgin. The method was applied satisfactorily to pharmaceutical preparations as well as biological fluids.     

Spectrophotometric determination of labetalol in pharmaceutical preparations and spiked human urine

Two simple and sensitive spectrophotometric methods were developed for the spectrophotometric determination of labetaolol (LBT). Both methods are based on the phenolic nature of the drug. The first method (Method I) is based on coupling LBT with diazotized benzocaine in presence of trimethylamine. A yellow colour peaking at 410 nm was produced and its absorbance is linear with the concentration over the range 1-10 microg ml(-1) with correlation coefficient (n=5) of 0.9993. The molar absorptivity was 2.633 x 10(4) l mol(-1) cm(-1). The second method (Method II) involves coupling LBT with diazotized p-nitroaniline in presence of sodium carbonate. An orange colour peaking at 456 nm was obtained and its absorbance is linear with concentration over the range 1-10 microg ml(-1) with correlation coefficient (n=5) of 0.99935. The stoichiometry of the reaction in both cases was accomplished adopting the limiting logarithmic method and was found to be 1:1. The developed method could be successfully applied to commercial tablets. The results obtained were in good agreement with those obtained using the official methods. No interference was encountered from co-formulated drugs, such as hydrochlorothiazide. The method was further extended to the in-vitro determination of LBT in spiked human urine. The % recovery (n=4) were 97.7+/-5.75 and 103.27+/-5.42 using the Methods I and II, respectively.     

Kinetic methods for the determination of atenolol in pharmaceutical preparations.

The fixed concentration and the fixed time methods were used for quantitative determination of atenolol employing 0.0515 M ammonium meta vanadate as an oxidant in 2.5 M sulphuric acid at 84 degrees C. The two methods are based on reaction rate measurements following the absorbance of vanadium (IV) species produced, spectrophotometrically at 750 nm. The applicability of the methods was tested by assaying atenolol in drug formulations and comparing the results obtained statistically with the BP method.     

Spectrophotometric determination of ketotifen in pharmaceutical preparations after isolation on ion-exchanger

Spectrophotometric method have been proposed for the determination of ketotifen in complex "Position" (Polfa-Poznań) samples after preliminary separation of excipients. For the determinations of the ketotifen in Pozitan a relative standard deviation of +/-2.0% was found.     

Spectrofluorimetric and micelle-enhanced spectrofluorimetric methods for the determination of gemfibrozil in pharmaceutical preparations

A spectrofluorimetric method for the determination of antihyperlipoproteinemic gemfibrozil was developed based on its native fluorescence. This method allows the determination of 0.10-6 microg ml(-1) gemfibrozil in aqueous solution (without using any buffer solution) with excitation and emission wavelengths of 276 and 304 nm, respectively. Detection and quantification limits were 0.03 and 0.10 microg ml(-1), respectively. The fluorescence properties of gemfibrozil in micellar media were also studied. It was shown that in the presence of 0.4% Brij-35 surfactant (pH 4.0, acetic acid-acetate buffer) about 2.4-fold enhancement can be achieved in the fluorescence of this drug. Based on the obtained results, a micelle-enhanced fluorescence method was also developed that is more sensitive than aqueous fluorescence method and has lower detection limit (0.02 microg ml(-1)). Both methods were applied satisfactorily to the determination of gemfibrozil in a commercial pharmaceutical formulation.