Validated stability-indicating methods for determination of cilostazol in the presence of its degradation products according to the ICH guidelines.

Sensitive and selective stability-indicating assay methods (SIAMs) are suggested for the determination of cilostazol (CIL) in the presence of its acid, alkaline and oxidative degradation products. Developing SIAMs is necessary to carry out any stability study. Stress testing of CIL was performed according to the International Conference on Harmonization (ICH) guidelines in order to validate the stability-indicating power of the analytical procedures. Stress testing showed that CIL underwent acid, alkaline and oxidative degradation; on the other hand, it showed stability towards photo- and thermal degradation. Two chromatographic SIAMs were developed, namely HPLC and HPTLC methods. The concentration range and the mean percentage recovery were 1.0-31.0 microg/ml and 99.96+/-0.46 and 0.6-14.0 microg/spot and 99.88+/-1.10 for HPLC and HPTLC methods, respectively. In addition, derivative spectrophotometric methods were developed in order to determine CIL in the presence of its acid degradation product; these were performed by using the third derivative spectra (3D) and the first derivative of the ratio spectra (1DD) methods. The linearity range and the mean percentage recovery were 2.0-34.0 microg/ml and 100.27+/-1.20 for the (3D) method, while they were 2.0-30.0 microg/ml and 99.94+/-1.18 for the (1DD) method. Also, two chemometric-assisted spectrophotometric methods, based on using partial least squares (PLS) and concentration residual augmented classical least squares method (CRACLS), for the determination of CIL were developed. Both methods were applied on zero order spectra of the mixtures of CIL and its acid degradation product, the mean percentage recovery was 100.03+/-1.09 and 99.91+/-1.27 for PLS and CRACLS, respectively. All methods were validated according to the International Conference on Harmonization (ICH) guidelines and applied on bulk powder and pharmaceutical formulations.

Membrane electrodes for the determination of glutathione.

Four glutathione (GSH)-selective electrodes were developed with different techniques and in different polymeric matrices. Precipitation-based technique with bathophenanthroline-ferrous as cationic exchanger in polyvinyl chloride (PVC) matrix was used for sensor 1 fabrication. beta-Cyclodextrin (beta-CD)-based technique with either tetrakis(4-chlorophenyl)borate (TpClPB) or bathophenanthroline-ferrous as fixed anionic and cationic sites in PVC matrix was used for fabrication of sensors 2 and 3, respectively. beta-CD-based technique with TpClPB as fixed anionic site in polyurethane (Tecoflex) matrix was used for sensor 4 fabrication. Linear responses of 1x10(-5) to 1x10(-4)M and 1x10(-6) to 1x10(-3)M with slopes of 37.5 and 32.0mV/decade within pH 7-8 were obtained by using electrodes 1 and 3, respectively. On the other hand, linear responses of 1x10(-5) to 1x10(-2) and 1x10(-5) to 1x10(-3)M with slopes of 47.9 and 54.3mV/decade within pH 5-6 were obtained by using electrodes 2 and 4, respectively. The percentage recoveries for determination of GSH by the four proposed GSH-selective electrodes were 100+/-1, 100.5+/-0.7, 100+/-1 and 99.0+/-0.8% for sensors 1, 2, 3 and 4, respectively. Determination of GSH in capsules by the proposed electrodes revealed their applicability for determination of GSH in its pharmaceutical formulations. Also, they were used to determine GSH selectively in presence of its oxidized form (GSSG). Sensor 4 was successfully applied for determination of glutathione in plasma with average recovery of 100.4+/-1.11%. The proposed method was compared with a reported one. No significant difference for both accuracy and precision was observed.

Derivative spectrophotometric and fluorimetric methods for determination of rofecoxib in tablets and in human plasma in presence of its photo-degradation product.

Rofecoxib (I) has been determined in the presence of its photo-degradation product (II) using first derivative spectrophotometry ((1)D) and first derivative of the ratio spectra ((1)DD) by measuring the amplitude at 316.3 and 284 nm for (1)D and (1)DD, respectively. (I) can be determined in the presence of up to 70% and 80% of (II) by the (1)D and (1)DD, respectively. The linearity range of both the methods was the same (5.8-26.2 microg ml(-1)) with mean percentage recovery of 100.08 +/- 0.84 and 100.06 +/- 1.06 for (1)D and (1)DD, respectively. (1)D method was used to study kinetics of (I) photo-degradation that was found to follow a first-order reaction. The t(1/2) was 20.2 min while K (reaction rate constant) was 0.0336 mol min(-1). Both methods were applied to the analysis of (I) in bulk powder and in pharmaceutical formulations. Also a spectrofluorimetric method is described to determine (I) at very low concentrations (25-540 ng ml(-1)) where (I) is converted to its photo-degradate (II), which possesses a native fluorescence that could be measured. The proposed method was applied for the analysis of tablets containing rofecoxib as well as to rofecoxib-spiked human plasma.