Determination of melatonin in blood plasma, using capillary gas chromatography and electron impact medium-resolution mass spectrometry.

Determination of the low concentrations (less than 10-100 pg ml-1) of melatonin in blood plasma by gas chromatography/mass spectrometry has previously required the use of negative ionization (electron capture) mass spectrometry, a technique particularly delicate to set up. We show that a general-purpose medium-resolution instrument gives adequate sensitivity in electron impact mode, when used with a capillary gas chromatographic column-switching device. A straightforward extraction procedure gives good specificity, and the limit of useful measurement is better than 10 pg per 1 ml sample.