Strata x c18 cartridge

Blood metabolite studies were performed by the procedure reported in previous literature.^{17 (link)} Blood samples were taken from rats (n = 2) at 10, 30, and 60 min after [¹⁸F]3 injection. Each blood sample was centrifuged for 3 min to separate plasma and blood coagulants. The plasma (0.3 ml) was retrieved, and 0.3 ml of acetonitrile was added to the plasma. The suspended solution was vortexed, and centrifuged for 3 min to precipitate protein and to obtain protein-free plasma as supernatant. The resulting supernatant was divided 2 parts. One part was used for measuring the total radioactivity and another part (0.3 ml) was loaded to a Strata-X C₁₈ cartridge (500 mg, Phenomenex Inc.) that had been purged with water. A series of elutions were performed using using 0.1% TFA/water and 0.1% TFA/acetonitrile in quantities: 95:5, 90:10, 85:15, 80:20, 70:30, 60:40, 30:70, 100% of 0.1% TFA/acetonitrile at a volume of 4 mL. The eluted fractions were collected in eight test tubes. A control experiment by injection of a small amount of [¹⁸F]3 onto a test cartridge elution described above indicated that the parent [¹⁸F]3 was collected in the seventh test tube exclusively. The radioactivities were measured using a 2480 Wizard^{2 (link)} Automatic Gamma Counter (PerkinElmer Inc., Waltham, MA).