Use of large particles support for fast analysis of methadone and its primary metabolite in human plasma by liquid chromatography–mass spectrometry

A bioanalytical method was developed for the quantitation of methadone (MTD) and its primary metabolite, (EDDP) in plasma. The extraction step was performed within a capillary column packed with large particles (35×0.3 mm I.D.; dp 30 μm) at high flow-rate conditions (450 μl/min). The separation was performed on a microbore analytical column (55×2 mm I.D.; dp 3 μm) coupled to a mass spectrometer (MS). This procedure was based on a column-switching unit. Analytes of interest were retained on the precolumn by hydrophobic interactions and backflushed from the precolumn to the analytical column. The detection was carried out with a MS single quadrupole equipped with an electrospray interface. The total analysis time was 6 min. The limits of quantification were evaluated at 10 and 25 ng/ml for MTD and EDDP, respectively. At this level, good accuracies were obtained for both analytes with repeatability values less than 18%.