Several chromatographic methods have been reported for the analysis of LA in various biological samples except for skin. Yet,no HPLC/ELS method has been reported for LA thus far. HPLC/ELS is a useful method employed to determine the lipid composition of different samples and the purity of lipid classes [21]. LA assays are essential for the development of drug delivery systems and for supporting the treatment for skin pathologies [22]. This is because knowledge of the exact LA amount present in the skin and its main layers, as the outermost layer, the stratum corneum, and the deeper layer, the dermis, is important for successful therapy. LA methods of analysis allow choosing an adequate topical formula-tion, the therapeutic dose, as well as to know LA bioavailability in the skin. For these reasons, we developed and validated HPLC methods considering the specific requirements as recommendedin standard guidelines [23,24]. The experimental conditions have been optimized to improve the sensitivity, retention time and resolution of the peaks. We adjusted the proportion of solvents used in the mobile phase, the oven temperature and the flow rates for the three methods (data not shown). The validation parameters for three HPLC methods are shown in Table 1. The results from analyses of the calibration curves are shown in Fig. 1.3.1