Specifically, in the HPLC/EC, the oxidation potential was adjusted to +1.1 V, and the concentration of the sodium dihydrogenphosphate solution was increased to 0.1 M, which gave the highest response for LA. The mobile phase was degassed with helium to remove oxygen, which can interfere with LA reduction.The LA peak presented a slight tail due the adsorption of LA on electrode surface. This phenomenon did not impair the method reliability and is in accordance with data reported previously [18].LA displayed linearity over a wide concentration range. Intra- andinter-day precision (coefficient of variation) was less than 6.5%. The accuracy of this method was greater than 90%, determined from the percentage recovery at 8, 2, 0.5 g/mL LA. The LLOD and LLOQ values were determined to be 1.0 and 0.91 ± 0.05 g/mL, respectively. The chromatograms for standard solutions and LLOQ of LA determined by HPLC/EC are shown in Fig. 2A. Routine cleaning of the surface of the electrode was performed to maintain the sensitivity [19]. In this way, the results obtained from skin analyses are reproducible and accurate as reported for LA in plasma sam-ples [25]. Therefore, HPLC/EC may be applied to samples with low concentrations of LA.