Hydrolytic stress degradation study and concomitant HPTLC estimation of thioctic acid and biotin in their combined capsules: greenness, blueness and whiteness assessment.

Stability testing and quality control assessment of active substances in single-pill combinations represent real challenges to drug analysts. This analytical challenge becomes more difficult when these drugs are non-chromophoric and co-formulated in disparate concentration ratio with few or no analytical methods reported in the literature for their concurrent quantification. This study deals with the development of HPTLC method for stability testing of hydrolytic degradation and simultaneous estimation of TH and BO in pure form, fresh and expired combined capsules. HPTLC separation was achieved using aluminium HPTLC plates precoated with silica gel 60 F-254 and mobile phase consisting of chloroform: methanol: ammonia (8.5:1.5:0.05, by volume). Scanning was performed at 215 nm. The designed method was validated as per the ICH guidelines. Excellent linearity was proved by high values of correlation coefficient not less than 0.99976 over concentration ranges of 2.5-30 and 2.5-20 µg/band for TH and BO, respectively. The limits of dectection were 0.58 and 0.33 µg/band while the limits of quantitation were 1.74 and 0.99 µg/band for TH and BO, respectively. The method proved to be precise, accurate and robust with values of RSD% and Er% not exceeding 2%. The designed method was found selective for the simultaneous estimation of BO and TH in pure form, in the presence of their degradation products, in valid and expired combined capsules. Both drugs were subjected to wet heat, acidic and basic hydrolysis. Both drugs were found liable to degradation (11-19%) under acidic (2.5 M HCl at room temperature for 30 min) and alkaline (3 M NaOH at room temperature for 30 min) hydrolytic conditions but they were found more stable under neutral hydrolytic conditions. Furthermore, Degradation kinetic study was accomplished to better understand the kinetics of their degradation under the employed stress conditions. Moreover, a tri-faceted assessment of the method's degree of greenness (Eco-Scale score is 80, AGREE score is 0.72 and MoGAPI score is 76), blueness (BAGI score is 82.5) and whiteness (score is 92.2%) was performed.