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).
Capsaicinoids, salicylic acid, methyl and ethyl salicylate, glycol monosalicylate, camphor and l-mentholare 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 mentionedactive compounds, no assay methods were found. Due to the differing physicochemical characteristics,two methods were developed and optimized simultaneously. The non-volatile capsaicinoids, salicylic acidand glycol monosalicylate were analyzed with liquid chromatography following liquid–liquid extraction,whereas the volatile compounds were analyzed with static headspace-gas chromatography. For the lattermethod, liquid paraffin was selected as compatible dilution solvent. The optimized methods were validatedin terms of specificity, linearity, accuracy and precision in a range of 80% to 120% of the expectedconcentrations. 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. Accuracywas assessed by performing replicate recovery experiments with spiked blank samples. Mean recoveryvalues 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 allthree levels. Finally, the method was successfully applied to the analysis of some real samples (cutaneous
sticks).
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