To 5 mL urine 300 µL 10 M potassium hydroxide solution and internal standard (for GC-MS deuterium labeled 11-nor-Δ9-THC-carboxylic acid) are added. The sample is vortexed and then hydrolysed at 60 °C for 15 min. The sample is cooled. 200 µL glacial acetic acid and 2 mL 50 mM ammonium acetate solution are added. If necessary the sample pH is adjusted to 6.0-7.0.

Column conditioning: 2 mL methanol, followed by 2 mL distilled water - equilibrate column with 2 mL 50 mM ammonium acetate buffer.

Sample application: Slowly force or aspirate the sample through the column (1-2 ml per min).

Column washing: Interferences are eluted with 10 mL methanol - water (1:1, v/v).

Drying: The column is dried for 10 min at high vacuum, washed with 2 mL acetonitrile and dried for another 2 min.

Elution: THC metabolites are eluted with 3 mL hexane - ethyl acetate - glacial acetic acid (75:25:1, v/v/v).