High-performance liquid chromatographic analysis of melatonin in human plasma and rabbit serum with on-line column enrichment

This paper describes the development of a simple and sensitive analytical method for the quantification of melatonin in human plasma and rabbit serum, using standard analytical equipment and on-line column enrichment without prior extraction, clean-up or derivatization. The analytical procedure was found to be accurate, precise and linear. For human plasma, the accuracy was 101% (range 89-106%), and the mean precision was 5% (range 2-9%) for all concentrations (0, 2, 10, 50 and 200 ng/ml) tested (n =6). The accuracy in rabbit serum was 101% (range 90-112%), and the mean precision was 13% (range 8-19%) for all concentrations (0, 2, 10, 50, 200 and 500 ng/ml) tested (n =6). The retention time of melatonin was about 8 min and the total recoveries were found to be approximately 65 and 85%, respectively, for human plasma and rabbit serum. The Limit of detection was found to be lower than 1 ng/ml for human plasma and around 2 ng/ml for rabbit serum. The method is, therefore, found to be suitable for melatonin bioavailability studies in rabbits and presumably also in humans. (C) 1998 Elsevier Science B.V. All rights reserved.