Derivative spectrophotometric analysis of benzophenone (as an impurity) in phenytoin.

Three simple and rapid spectrophotometric methods were developed for detection and trace determination of benzophenone (the main impurity) in phenytoin bulk powder and pharmaceutical formulations. The first method, zero-crossing first derivative spectrophotometry, depends on measuring the first derivative trough values at 257.6 nm for benzophenone. The second method, zero-crossing third derivative spectrophotometry, depends on measuring the third derivative peak values at 263.2 nm. The third method, ratio first derivative spectrophotometry, depends on measuring the peak amplitudes of the first derivative of the ratio spectra (the spectra of benzophenone divided by the spectrum of 5.0 µg/mL phenytoin solution) at 272 nm. The calibration graphs were linear over the range of 1-10 µg/mL. The detection limits of the first and the third derivative methods were found to be 0.04 µg/mL and 0.11 µg/mL and the quantitation limits were 0.13 µg/mL and 0.34 µg/mL, respectively, while for the ratio derivative method, the detection limit was 0.06 µg/mL and the quantitation limit was 0.18 µg/mL. The proposed methods were applied successfully to the assay of the studied drug in phenytoin bulk powder and certain pharmaceutical preparations. The results were statistically compared to those obtained using a polarographic method and were found to be in good agreement.

Spectrofluorimetric determination of ciclopirox olamine via ternary complex with Tb(III) and EDTA.

A highly sensitive and selective spectrofluorimetric method was developed for the determination of ciclopirox olamine in raw material and in dosage forms. The proposed method is based on the formation of a ternary complex with Tb(III) in the presence of ethylenediaminetetraacetic acid. It was found that this complex manifests intense fluorescence at lambda(em) 489 and 545 nm with excitation at 295 nm. Different experimental parameters affecting the fluorescence intensity of the complex were carefully studied and incorporated into the procedure. Under the described conditions, the method is applicable over the concentration range 30-150 and 10-70 ng mL(-1) with minimum detectability of 6.7 and 0.9 ng mL(-1) at lambda(em) 489 and 545 nm, respectively. The mean percentage recovery at lambda(em) 489 and lambda(em) 545 nm ranged between 98.7 and 100.2 for the pure substance, solution, and cream. Relative error of 0.1-0.4% and RDS of up to 0.9% were estimated at lambda(em) 489 and 545 nm. A proposal of the reaction pathway is given.