Multi-element method for determination of trace elements in sunscreens by ICP-AES

Abstract

An inductively coupled plasma atomic emission spectrometric (ICP-AES) method was developed for multi-element analysis of sunscreen creams and lotions. The objective was the simultaneous determination of Ti (TiO 2 being is the only authorized inorganic UV filter in the European Union) and several minor, trace or toxic elements (Al, Zn, Mg, Fe, Mn, Cu, Cr, Pb and B) in the final products. Two alternative pretreatment procedures were examined: (i) total acid digestion in closed pressurized vessels prior to sample introduction into the plasma and (ii) direct introduction of sample in the form of emulsified slurry. The latter was proved inefficient for several types of creamy samples due to their high viscosity and insolubility. Several acid mixtures were examined for wet digestion because of the complex and fatty matrix of creams and lotions. Plasma parameters like nebulizer argon gas flow rate and radiofrequency incident power were optimized in order to improve the atomization. The recovery of the proposed acid digestion method was evaluated using spiked samples. The calculated recoveries were 95.0% for Ti, 98.2% for Zn and 101.3% for Fe, and the detection limits were 0.2 μg g −1 for Ti, 0.2 μg g −1 for Zn and 0.5 μg g −1 for Fe, respectively. Possible interference from the presence of Ti on the sensitivity of each analyte was examined. Finally the method was applied successfully to several commercial sun protection products and the results were compared with those obtained by atomic absorption spectrometry as reference method.