Extraction of THC-COOH from urine using ISOLUTE® HAX cartridges

Introduction

This method was developed for the extraction of the tetrahydrocannabinol carboxylic acid metabolite (THC-COOH) from urine using a mixed non-polar and anion exchange retention mechanism. Typical recoveries of the analyte are > 75%.

Figure 1: Structure of THC-COOH

Due to the presence of a carboxylic acid group, this compound will require derivatization prior to analytical determination by GC-MS.

Extraction procedure

Format

ISOLUTE® HAX 200 mg/10 mL, Part Number 903-0020-H

Matrix

The matrix is of high ionic strength and contains a number of potential interference compounds. The mixed retention mechanism used in this extraction allows a rigorous interference elution procedure.

Pre-treatment

Add 100 μL of internal standard to 3 mL of urine. Hydrolyse with 0.1 mL of NaOH, 10 M. Heat for 15 minutes at 60 ˚C. Cool. Add 0.5 mL of glacial acetic acid.

Condition

Condition the cartridge with 1 mL of methanol at 2 mL/min.

Equilibration

Rinse the cartridge with 1 mL of deionized water at 2 mL/min.

Sample loading

Apply sample at a flow rate of 2 mL/min.

Interference elution

Rinse cartridge with 0.3 M ammonium acetate buffer, (pH 8, 1 mL), at 2 mL/min. Rinse cartridge with 1 mL of 20 mM ammonium acetate buffer at 2 mL/min, followed by 1 mL of methanol at 2 mL/min.

Analyte elution

Elute analyte with 1 mL of methanol/ethyl acetate/acetic acid 48:50:2, at 1 mL/min.

Analytical method GC-MS

Cartridge

DB-5 capillary, 15 m x 0.25 mm I.D. x 0.25 μm

Initial temperature

180 ˚C for 1 min.

Temperature ramp

20 ˚C/min.

Final temperature

280 ˚C for 1 min.

Detection

MS

Reagents

1.    10 M NaOH
2.    Glacial acetic acid
3.    Methanol
4.    0.3 M ammonium acetate buffer, pH between 7.5 and 8.5
5.    20 mM ammonium acetate buffer, pH between 7.5 and 8.5
6.    Methanol/ethyl acetate/acetic acid 48:50:2

Ordering information

Literature Number: IST1035A