A spectrofluorimetric method is described for the assay of lysergic acid diethyladmide (LSD) at nanogram levels in human plasma in the presence of a variable blank. The procedure makes use of the observation that ultra-violet light catalyses the hydration of LSD to the non-fluorescent lumi-derivative. The difference in fluorescence
of plasma extracts before and after intense ultra-violet irradiation is a measure of LSD concentration. This technique has been used for the assay of LSD in plasma following the oral administration of the drug at a dose of approximately 2ug per kg body weight.
The mean plasma levels of the three groups are given in Table II. LSD was detectable for up to five hours in those men who had fasted or had eaten a light meal. Plasma samples were not taken later than some 2.5 h after dosing from those men who had eaten a full meal, but it is unlikely that the drug would have been present in sufficient concentration for its accurate estimation at 5 h.
