title: Supercritical fluid extraction of 11C-labeled metabolites in tissue using supercritical ammonia.
abstract: Supercritical fluid extraction (SFE) of 11C-labeled tracer compounds and their metabolites from biological tissue was performed using supercritical ammonia in an attempt to develop a rapid extraction procedure that allowed subsequent analysis of the labeled metabolites. Metabolites were extracted from kidneys and brain in rats given in vivo injections of the radiotracers O-[2-11C]acetyl-L-carnitine and N-[11C]methylpiperidyl benzilate, respectively. Only a minimal sample pretreatment of the tissue was necessary, i.e., cutting into 10-20 pieces and mixing with the drying agent Hydromatrix, before it was loaded into the extraction vessel. Extraction efficiency was measured for SFE at temperatures over the range of 70-150 degrees C and a pressure of 400 bar. For O-[2-11C]acetyl-L-carnitine, 66% of the radioactivity was trapped in the collected fractions and 12% remained in the extraction vessel. For the more lipophilic N-[11C]methylpiperidyl benzilate, 93% of the activity was collected and less than 1% remained in the extraction vessel. Labeled metabolites were analyzed by LC and also, in the case, of O-[2-11C]acetyl-L-carnitine by LC/MS. The complete extraction procedure, from removal of the biological tissue until an extract was ready for analysis, was 25 min, corresponding to about one half-life of the radionuclide 11C.
authors.affiliation: Uppsala University PET Centre, Department of Analytical Chemistry, Sweden.
authors.forename: G B
authors.initials: GB
authors.lastname: Jacobson
authors.forename: R
authors.initials: R
authors.lastname: Moulder
authors.forename: L
authors.initials: L
authors.lastname: Lu
authors.forename: M
authors.initials: M
authors.lastname: Bergström
authors.forename: K E
authors.initials: KE
authors.lastname: Markides
authors.forename: B
authors.initials: B
authors.lastname: Långström
mesh_terms: D000108:Acetylcarnitine / Q000032:analysis / Q000493:pharmacokinetics; D000641:Ammonia / Q000737:chemistry*; D000818:Animals; D002250:Carbon Radioisotopes; D002853:Chromatography, Liquid; D018697:Nootropic Agents / Q000032:analysis / Q000493:pharmacokinetics; D051381:Rats; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002250:Carbon Radioisotopes; D018697:Nootropic Agents; D000108:Acetylcarnitine; D000641:Ammonia