Comparison of gas chromatography mass spectrometry methods for the determination of Δ9-tetrahydrocannabinol in plasma

A method for the identification of Δ9‐tetrahydrocannabinol by gas chromatography mass spectrometry has been developed, and this method has been compared with other techniques, such as detection via thin‐layer chromatography using tritium labeled Δ9‐tetrahydrocannibinol and a dual gas chromatographic method. The gas chromatographic mass spectrometric method was found to be equal or superior to other techniques and has the added advantage of being highly specific for the compound analyzed. An alternate approach using chemical ionization is also described; however, this procedure does not show significant advantages over the electron impact method. These methods show a practical lower detection limit of 500 pg ml−1 of plasma in clinical practice.