Application of optimized dispersive liquid-liquid microextraction for determination of melatonin by HPLC-UV in plasma samples

Melatonin (N-acetyl-3-(2-aminoethyl)-5-methoxyindole) is biologically active as a neurohormone and antioxidant agent. The optimized dispersive liquid-liquid microextraction (DLLME) followed by high-performance liquid chromatography-ultra violet detection (HPLC-UV) was used for the analysis of melatonin in human plasma. Influence variables such as volume of extracting (carbon tetrachloride: CCl4) and dispersing solvents (acetonitrile: ACN), pH and ionic strength, extraction time and centrifugation time were screened in a 2(6-2) fractional factorial design (FFD) and then the significant variables were optimized by using a central composite design (CCD). At optimum conditions values of variables set as pH 6.0, 1.5 mL ACN, 140 mu L CCl4, 1.0 min extraction time and 3.0 min centrifugation at 4500 rpm. At optimum conditions method has linear response over 2.0-500.0 ng mL(-1) with detection limit of 0.5 ng mL(-1) with relative standard deviations (RSDs) less than 5.0%. The values of intra-day and inter-day RSD were 4.3% and 8.5%, respectively. The method was applied successfully for the analysis of melatonin in plasma sample. (C) 2014 Elsevier B.V. All rights reserved.