After testing several chromatographic systems described in the literature, the optimal operating conditions were retained to develop a simple and rapid method grouping TLC and HPLC/UV for separation, identification and dosage of kojic acid (CAS RN 501-30-4) or arbutine (CAS RN 497-76-7) in skin-whitening cosmetic products. The screening is carried out by TLC on cellulose plate and by TLC on silicagel plate with UV indicator and polar mobile solvent. Regarding identification and quantitative determination by HPLC/UV, the best results were obtained by direct phase chromatography, using a polar stationary phase greffed with diol groups and a polar buffered mobile phase at PH 2,5. Intralaboratory prevalidation tests were carried out on the HPLC method: detection limit, linearity and intralaboratory repeatability of standard curves and repeatability of samples quantitative determination.

We developed a method for the quantitative determination of sodium fluoride (NaF), sodium monofluorophosphate (SMFP) and amine fluoride (AmF) in toothpastes on the Belgian market. Samples were suspended in water and the determination was made using anion chromatography with conductivity detection after chemical suppression. The described ion chromatographic method is an easy and reliable isocratic high-performance liquid chromatography method for the determination of total soluble fluoride content in toothpastes. The analytical repeatability and reproducibility, the matrix effects and the method's decision limit of three different toothpastes containing NaF, SMFP and AmF at a concentration close to the permitted one of 0.15 g % total F are determined. All the samples analysed are in conformity with the Cosmetics Directive 76/768/EC; none exceeds the limit of 0.15 g %.

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 % (re: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.

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