Chromium, Cobalt and Nickel in eye shadows: pigments concentration and size distributions through a combined SdFFF-AAS study

It is well-known that Nickel (Ni), Cobalt (Co)and Chromium (Cr) might give rise to contact dermatitis in subjects with pre-existing allergy. The use of metal ions in cosmetic formulation is regulated by the Directive 76/768/EEC, which forbids the presence of Co, Ni and Cr in cosmetics but allows their presence in very low quantities, defined as “impurities”. The scientific literature proposes that Ni or Co should not exceed 5 ppm (µg/g) while the suggested amount to minimize the risk of sensitization in particularly sensitive subjects should be as low as 1 ppm. In this work several eye shadows, available for sale in Italy, were analysed to determine the Cr, Co and Ni concentrations and to describe the particle size distribution (PSD) of the water compatible particles contained in the powders. To isolate the water compatible particles, the samples were treated with a ternary mixture of solvents (H2O/ethanol/exan), and the PSDs were determined through Sedimentation Field Flow Fractionation (SdFFF) analyses. The fractograms were recorded at regular time intervals (4 hours) and after 24 hours to follow the PSD time evolution, to highlight the water soluble and insoluble microparticles. The separation results were confirmed with SEM observations and, when possible, through the Atomic Absorption Spectroscopy (AAS) specific element detection. The total concentration of Cr, Co and Ni was determined by AAS after a sample acid digestion done in a microwave oven. The Cr concentration was always higher than the other elements; in one sample it was ~ 150 mg/g, so that in this product also the water-soluble Cr concentration was determined. All samples contained mainly micro-sized particles, so that the toxicity due to the presence of nano-material was excluded, however the total Ni and Cr concentration was in the 70% of cases higher than the suggested limit of 5 ppm.