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  • Optimization and validation of liquid chromatography and headspace-gas chromatography based methods for the quantitative determination of capsaicinoids, salicylic acid, glycol monosalicylate, methyl salicylate, ethyl salicylate, camphor and l-menthol in a topical formulation.

Optimization and validation of liquid chromatography and headspace-gas chromatography based methods for the quantitative determination of capsaicinoids, salicylic acid, glycol monosalicylate, methyl salicylate, ethyl salicylate, camphor and l-menthol in a topical formulation.

Journal of pharmaceutical and biomedical analysis (2011-11-19)
Jochen Pauwels, Ward D'Autry, Larissa Van den Bossche, Cédric Dewever, Michel Forier, Stephanie Vandenwaeyenberg, Kris Wolfs, Jos Hoogmartens, Ann Van Schepdael, Erwin Adams
ABSTRACT

Capsaicinoids, salicylic acid, methyl and ethyl salicylate, glycol monosalicylate, camphor and l-menthol are widely used in topical formulations to relieve local pain. For each separate compound or simple mixtures, quantitative analysis methods are reported. However, for a mixture containing all above mentioned active compounds, no assay methods were found. Due to the differing physicochemical characteristics, two methods were developed and optimized simultaneously. The non-volatile capsaicinoids, salicylic acid and glycol monosalicylate were analyzed with liquid chromatography following liquid-liquid extraction, whereas the volatile compounds were analyzed with static headspace-gas chromatography. For the latter method, liquid paraffin was selected as compatible dilution solvent. The optimized methods were validated in terms of specificity, linearity, accuracy and precision in a range of 80% to 120% of the expected concentrations. For both methods, peaks were well separated without interference of other compounds. Linear relationships were demonstrated with R² values higher than 0.996 for all compounds. Accuracy was assessed by performing replicate recovery experiments with spiked blank samples. Mean recovery values were all between 98% and 102%. Precision was checked at three levels: system repeatability, method precision and intermediate precision. Both methods were found to be acceptably precise at all three levels. Finally, the method was successfully applied to the analysis of some real samples (cutaneous sticks).

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Methyl salicylate, ReagentPlus®, ≥99% (GC)
Supelco
L-Menthol, Pharmaceutical Secondary Standard; Certified Reference Material
Supelco
Methyl salicylate, analytical standard
Supelco
Methyl salicylate, Pharmaceutical Secondary Standard; Certified Reference Material
Sigma-Aldrich
Methyl salicylate, ≥98%, FCC, FG
Sigma-Aldrich
Dihydrocapsaicin, from Capsicum sp., ≥85%
Sigma-Aldrich
Ethyl salicylate, 99%
Sigma-Aldrich
Ethyl salicylate, ≥99%, FCC, FG
Sigma-Aldrich
Methyl salicylate, tested according to Ph. Eur.
Sigma-Aldrich
Ethylene glycol monosalicylate, ≥98.0% (GC)
Sigma-Aldrich
Methyl salicylate, BioXtra
Hydroxyethyl salicylate, European Pharmacopoeia (EP) Reference Standard