Purpose: Ambrisentan (ABS) is an antihypertensive drug used in the treatment of pulmonary atrial hypertension. The survey of literature for ABS revealed only two spectrophotometric methods for its quantification. The reported methods lack the sensitivity. This study is aimed at developing two sensitive extractive spectrophotometric methods for the determination of ABS in bulk and in tablets.Methods: The proposed methods are based on the formation of colored chloroform extractable ion-pair complexes of ABS with methylene blue (MB method) and safranine O (SO method) in buffered solution at pH 9.8. The extracted complexes showed maximum absorbance at 525 and 515 nm for methylene blue and safranine O, respectively.Results: In both the methods, the calibration curve was linear from 1-15 mg mL-1 of drug. Apparent molar absorpitivities were 1.7911 x 105, 2.3272 x 105 L mol-1 cm-1; Sandell’s sensitivities were 0.0215, 0.0162 mg cm-2; LOD were 0.182, 0.175 mg mL-1; LOQ were 0.551, 0.531 mg mL-1 for methods MB and SO, respectively. The relative standard deviation and percent recovery ranged from 0.206–1.310% and 99.0-101.5%, respectively.Conclusion: The results demonstrate that the proposed methods are sensitive, precise, accurate and inexpensive. These methods can easily be used for the assay of ABS in quality control laboratories.

A new spectrophotometric method for the assay of hydralazine hydrochloride in bulk and dosage forms has been developed. The procedure is based on a condensation reaction between alcoholic solution of hydralazine and acidic solution of pdimethylaminobenzaldehyde to generate an instant greenish-yellow coloured product. The hydrazone formed absorbed visible light strongly and optimal detector response was obtained at a wavelength of 470 nm with a molar absorptivity of 3.652x103 1 mol-1 cm-1. Optimization of temperature and time revealed 30 oC and 10 min as the best conditions for optimal color formation, while methanol was found to be the most suitable alcohol as diluting solvent. The reaction product is stable for at least 24 h. Beer’s law was obeyed in the concentration range of 2-10 mg ml-1. Recovery studies over three days gave a mean recovery of 101.87% with a relative standard deviation of 1.29%. There was no interference from commonly used tablet excipients. There was no significant difference between the results obtained with the new method and the BP iodimetric method (p>0.05). The proposed method is simple, sensitive, rapid and economical, and could find application as an in-process quality control method for hydralazine.

A simple, rapid and sensitive method has been developed for determination of traces of tellurium(VI) (0.096-1.250 mu g/mL) based on its catalytic effect on the reduction reaction of toluidine blue by sulfide ion at pH 4. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of the dyestuff at 628 nm by the fixed time method. The detection limit is 80 ng/mL and the relative standard deviation for 1 mu g/mL tellurium is 2.2%.

Mixtures of food colorants, containing new coccine, ponceaue 6R and scarlet GN were simultaneously analyzed by spectrophotometry without previous chemical separation. Sixty mixtures of colorants with three-components were evaluated and the spectrograms were smoothed through the use of seven experimental points. The multivariate data consisted of normal, first- and second-derivative absorbance spectra (λ=5 nm) registered from 300-650 nm. The data obtained from experiments were processed by PLS method and the proposed method was applied satisfactorily for determination of these colorants in two commercial food products.

A simple and sensitive extractive spectrophotometric method is described for determination of tropicamide. The method is based on the reaction of tropicamide and bromocresol green. The ion-paired colored complex was extracted with chloroform at pH 3. The extracted complex showed maximum absorbance at 423 nm. The complex was stable up to 2 days and obeyed Beer's law over the concentration ranges of 1.32-100.81 mg/ml. No significant interference was observed from the excipients, coloring and flavoring agents commonly used in the tropicamide pharmaceutical preparations. The proposed method was applied successfully for determination of tropicamide in commercial eye drop dosage forms.

A new spectrophotometric method has been developed for the assay of nadolol in pure form and in tablets. The assay procedure is based on a derivatization methodology employing 4-carboxyl-2,6-dinitrobenzene dizonium ion (CDNBD) as a diazo coupling reagent. The azo dye formed between nadolol and CDNBD absorbed visible light at the wavelength maximum of 416 nm (λmax) demonstrating a bathochromic shift from the absorption maximum of nadolol. Optimization studies established an optimal reaction time of 10 min at 60 oC. The assays were linear over 1.25-10 μg ml-1 of nadolol, and the reaction occurred by a 3:1 reagent/drug stoichiometric ratio. The method is found to be selective and has a lower detection limit of 0.29 μg ml-1. Recovery studies over three days gave mean recovery of 101.4% (RSD 3.0%). This new method has been successfully applied in the determination of nadolol and nadolol/bendroflumethiazide tablets with accuracy and precision similar to the official (USP) HPLC procedure (p > 0.05). The new procedure has the advantages of high sensitivity, lower limit of detection and could find application as an in-process quality control method for nadolol.