Spectrofluorimetric study on fluorescence quenching of tyrosine and l-tryptophan by the aniracetam cognition enhancer drug: quenching mechanism using Stern-Volmer and double-log plots.

A novel approach on fluorescence quenching of tyrosine and l-tryptophan is presented for spectrofluorimetric determination of aniracetam in drug substances and products. The quenching mechanism was investigated using Stern-Volmer plots and ultraviolet spectra figures of quencher-fluorophore mixtures. Binding constant and stoichiometry were calculated using double-log plots.

Development and validation of spectrophotometric, TLC and HPLC methods for the determination of lamotrigine in presence of its impurity.

Three reliable, rapid and selective methods have been developed and validated for the determination of lamotrigine in the presence of its impurity, 2,3-dichlorobenzoic acid. The first method is spectrophotometric method using p-chloranilic acid forming a colored product with lambda(max) 519+/-2 nm. All variables affecting the reaction have been investigated and the conditions were optimized.

A comparative study on various spectrometries with thin layer chromatography for simultaneous analysis of drotaverine and nifuroxazide in capsules.

Three spectrophotometric methods including Vierordt's method, derivative, ratio spectra derivative, and thin layer chromatography (TLC)-UV densitometric method were developed for simultaneous determination of drotaverine HCl (DRT) and nifuroxazide (NIF) in presence of its impurity, 4-hydroxybenzohydrazide (4-HBH). In Vierordt's method, (E(1 cm)(1%)) values were calculated at 227 and 368 nm in the zero-order spectra of DRT and NIF. By derivative spectrophotometry, the zero-crossing method, drotaverine HCl was determined using the second derivative at 245 nm and the third derivative at 238 nm, while nifuroxazide was determined using the first derivative at 399 nm and the second derivative at 411 nm.

Spectrophotometric determination of some drugs for osteoporosis.

Three simple, accurate and sensitive spectrophotometric methods are developed for the determination of some new drugs for the treatment of osteoporosis: risedronate sodium (I), alendronate sodium (II) and etidronate disodium (III). The first method is based on the measurement of difference in absorbance (Delta A) of risedronate sodium in 0.01 mol l(-1) hydrochloric and 0.