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−1 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−1 and the limit of quantitation (LOQ) was 2.8 μg mL−1, 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.
Peptides are a very popular category of cosmetic ingredients covering a wide range of applications in cosmetics. Hydrophilic interaction liquid chromatography is promising for the analysis and separation of such polar substances. In this work, the chromatographic behaviour of oligopeptide‐20 and oligopeptide‐24 was initially investigated on a zwitterionic ZIC®‐HILIC analytical column under isocratic elution with UV detection. Then, a hydrophilic interaction liquid chromatography with positive ion electrospray mass spectrometric assay was developed and validated for the quantitation of these peptides in cosmetic creams. All analytes were separated by using a polymeric zwitterionic ZIC®‐pHILIC analytical column (150.0 × 2.1 mm i.d., particle size 3.5 μm, 200 Å) with isocratic elution. The mobile phase was composed of a 28% 32.5 mM ammonium formate water solution pH 9.5 in acetonitrile and pumped at a flow rate of 0.25 mL min−1. A run time of less than 11 min for each sample made it possible to analyze a large number of samples per day. This is the first reported application of hydrophilic interaction liquid chromatography in the simultaneous determination of oligopeptide‐20 and oligopeptide‐24 in cosmetic creams and it can be used to support routine quality control of these products.
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