Experimental and statistical validation of HPLC analysis of hydroquinone and its 4-methoxyphenol, 4-ethoxyphenol and 4-benzyloxyphenol ethers in cosmetic products

Summary

The isocratic HPLC analysis of hydroquinone and its derived ethers in cosmetic preparations, as described in the sixth Directive 95/32/EC of the European Commission, was investigated with a view to determining the fundamental validation parameters of the technique.

The calibration lines are highly linear with coefficients of determination >0.9996; the slopes of the calibration equations as well as the slopes normalised to the standard deviations indicate increased sensitivities for all compounds. The method is very reproducible; both the repeatability and the intermediate precision confirm a system performance of <2% variation; the limits of repeatability and intermediate precision are consistently <6% for every compound studied. The detection limits correspond to concentrations of 0.03 and 0.02% (m:m) for hydroquinone and the derived ethers, respectively. Application of the response factor calculation gives reliable results and signifies a practical and economic advantage when compared to laborious calibration with several replicate standard injections. Comparison of the response factor and calibration techniques did not reveal significant differences. The obviously insufficiently efficient extraction preceding chromatographic analysis might constitute the only drawback of the method, especially when the concentrations applied border the allowable.