Determination of melatonin in biological samples by capillary electrophoresis

The determination of melatonin (MLT) in physiological samples was investiga ted using capillary electrophoresis (CE). Mouse blood was collected in tube s containing EDTA, centrifuged at 1500 g for 20 min at 4 degrees C, and sto red at -20 degrees C. Plasma samples were extracted with dichloroethane, ce ntrifuged and the aqueous phase was discarded. Then the organic phase was e vaporated to dryness. The residue was dissolved in deionized water and filt ered with a microfilter (0.22 mu m). Separations were carried out using a C E system equipped with a fused silica capillary [80 cm (effective length 52 cm)X75 mu m I.D.] and an ultraviolet-visible detector (200 nm), and progra mmed to provide 25 mM 2-(N-morpholino)ethanesulfonic acid (pH 5.7). Injecti on was performed hydrostatically by elevating the sample by 10 cm at the ca thodic side of the capillary. The calibration curve, reproducibility, recov ery and limit of detection were examined, and validation of the method was performed. The result showed that MLT in blood could be easily determined w ith the new method. (C) 1999 Elsevier Science B.V. All rights reserved.