Quantitative Determination of Alpha-Lipoic Acid in SLS Micellar Medium Utilizing Inhibitory Kinetic Approach

Document Type : Research Paper


1 Department of Chemistry, GLA University, Mathura, 281006, U.P., India

2 Department of Chemical Engineering, Malaviya National Institute of Technology, Jaipur, India

3 Department of Chemistry, DDU Gorakhpur University, Gorakhpur, 273001, UP (India)

4 Department of Chemistry, B. N College of Engineering & Technology, Lucknow, U.P., India


A novel, repeatable, and swift kinetic approach for determining alpha-lipoic acid (ALA) in sodium lauryl sulfate (SLS) micellar medium has been presented, and it has been connected to ALA determination in drug formulations. The approach is based on ALA inhibitory property. ALA (containing two sulfur atoms) forms a chelate with Hg2+, lowering the effective [Hg(II)], and ultimately, the Hg2+ catalyzed cyanide substitution rate from [Ru(CN)6]4- by nitroso-R-salt (N-R-salt). Fixed times of 5 and 10 minutes were chosen under optimal reaction conditions with [N-R-salt] = 0.45 mM, pH = 7.0 ± 0.02, Temp = 45 ± 0.2 °C, I = 0.1 M (NaClO4), [Ru(CN)64-] = 42.5 µM, [Hg+2] = 0.25 mM, and [SLS] = 8.5 mM to calculate the absorbance at 525 nm associated with the final substitution product [Ru(CN)5 N-R-salt]3-. ALA's inhibiting influence on the Hg2+ catalyzed cyanide substitution with N-R-salt from [Ru(CN)6]4-, has been represented by a modified mechanistic approach. The concentration of ALA in various water specimens can be measured at the micro-level down to 2.5 µM using the established kinetic spectrophotometric approach. The suggested method is highly reproducible and has been effectively applied to accurately quantify the ALA in pharmaceutical samples. Even as much as 1000 with [ALA], Excipients used in medications do not significantly hinder the determination of ALA.