Development and validation of a reversed-phase high-performance liquid chromatographic method for the quantitation and stability of α-lipoic acid in cosmetic creams.

Objective: To develop and validate a simple reversed-phase HPLC method for the quantitation and evaluation of stability of α-lipoic acid in cosmetics, according to International Conference on Harmonization (ICH) Guidelines.

Methods: The chromatography was performed on a reversed-phase Luna C18, analytical column (150 × 4.6 mm id, 5 μm particle size) with a mobile phase of potassium dihydrogen phosphate (pΗ 4.5; 0.05 M) and acetonitrile (60:40, v/v) and a flow rate of 1.0 mL min with UV detection at 340 nm. Accelerated and long-term stability studies of α-lipoic acid in cosmetic cream were conducted under various degradation conditions including acid, basis, oxidation, and thermal and photolytic degradation, according to European Medicines Agency Guidelines CPMP/ICH/2736/99.

Results: The limit of detection (LOD) for the cosmetic cream was 0.9 μg mL and the limit of quantitation (LOQ) was 2.8 μg mL , while the retention time was 7.2 min. The method proved to be linear, precise and accurate. The stability results demonstrated the selectivity of the proposed method to the analysis of α-LA, and the degradation products were determined and evaluated in specific stress conditions in cosmetic creams. The applicability of the method was tested in two different developed cosmetic products (cream with 1.5 % w/w and emulsion with 1.0 % w/w of LA) and proved to be reliable.

Conclusion: A reversed-phase HPLC-UV method was developed and fully validated for the analysis of α-lipoic acid in cosmetics. It is the first reported application on the quantitation of lipoic acid in cosmetic creams, while at the same time evaluates the stability in forced degradation conditions, in new cosmetic formulations. It proved to be suitable for the reliable quality control of cosmetic products, with a run time of <8 min that allows for the analysis of large number of samples per day.