Glucuronide cleavage is carried out by mixing 1 mL urine, 2 mL water, 3 mL methanol and 600 µL 10 M KOH solution. After shaking at 50 °C for 15 min 500 µL 6 M HCl solution are added. The sample is adjusted to pH 5-6 by adding 5-10 drops glacial acetic acid. After centrifugation the supernatant is subject to solid phase extraction.

Column conditioning: 3 mL methanol, followed by 3 mL 0.1 M acetate buffer (pH 7)

Sample application: Aspirate slowly the sample through the column without vacuum (1-2 mL per min).

Column washing: Elute interferences with 3 mL acetate buffer (pH 4, 0.1 M) - MeOH (1:1, v/v) followed by 3 mL water - methanol (1:1, v/v)

Drying: Dry the sample 5 min in vacuum.

Elution: Elute THC and metabolites with 1.5 mL acetone - glacial acetic acid (99:1, v/v).