A stability-indicating gas chromatography (GC) method has been developed and validated for the quantitative determination of divalproex sodium impurities in pharmaceutical preparation. A technique has been developed whereby the peak purity of a compound with poor UV detection can be determined using a gas chromatograph coupled with a mass spectrometer. The drug products were subjected to hydrolysis, oxidation, photolysis, and heat to apply stress conditions. The stability-indicating nature of the method has been proven by establishing peak purity of all stressed samples. The chromatographic separation was performed on a fused silica capillary (Quadrex-FFAP, 30 meter, 0.32 mm and 1 microm film thickness) column. The method validation results indicate that the method is specific, accurate, linear, reproducible, rugged, and robust. The effectiveness of the technique was demonstrated with stability sample analysis of divalproex sodium in its pharmaceutical preparation.

In this work, a new degradation product of Aspirin was isolated, characterized and analyzed along with other impurities. New unknown degradation product referred as UP was observed exceeding the limit of ICH Q3B identification thresholds in the stability study of Aspirin and Dipyridamole capsule. The UP isolated from the thermal degradation sample was further studied by IR, Mass and (1)H NMR spectrometry, revealing structural similarities with the parent molecule. Finally, UP was identified as a new compound generated from the interaction of Aspirin and Salicylic acid to form a dehydrated product. A specific HPLC method was developed and validated for the analysis of UP and other Aspirin impurities (A, B, C, E and other unknown degradation products). The proposed method was successfully employed for estimation of Aspirin impurities in a pharmaceutical preparation of Aspirin (Immediate Release) and Dipyridamole (Extended Release) Capsules.

A selective, specific and sensitive ultra high pressure liquid chromatography (UHPLC) method was developed for determination of tacrolimus degradation products and tautomers in the preparation of pharmaceuticals. The chromatographic separation was performed on Waters ACQUITY UPLC system and BEH C₈ column using gradient elution of mobile phase A (90:10 v/v of 0.1% v/v triflouroacetic acid solution and Acetonitrile) and mobile phase B (90:10 v/v acetonitrile and water) at a flow rate of 0.6 mL min⁻¹. Ultraviolet detection was performed at 210 nm. Tacrolimus, tautomers and impurities were chromatographed with a total run time of 25 min. Calibration showed that the response of impurity was a linear function of concentration over the range 0.3-6 µg mL⁻¹ (r² ≥ 0.999) and the method was validated over this range for precision, intermediate precision, accuracy, linearity and specificity. For precision study, percentage relative standard deviation of each impurity was < 15% (n = 6). The method was found to be precise, accurate, linear and specific. The proposed method was successfully employed for estimation of tacrolimus impurities in pharmaceutical preparations.