Determination of delta 9-tetrahydrocannabinol-11-oic acid in urine as its pentafluoropropyl-pentafluoropropionyl derivative by GC/MS utilizing negative ion chemical ionization.

A rapid and sensitive GC/MS method for the determination of delta 9-tetrahydrocannabinol-11-oic acid in urine is presented. Enzymically hydrolyzed urine was extracted with hexane/ethyl ether followed by a one-step derivatization procedure with a mixture of pentafluoropropionic anhydride and pentafluoropropanol. By using negative ion chemical ionization and selected ion monitoring, a 200-fold higher detectability was observed, compared with El or positive ion chemical ionization under the conditions used. Samples were analyzed with split injection on a fused silica capillary column with a total analysis time of less than four minutes. A deuterium labelled analogue was used as internal standard and the precision for the overall method was measured to 3.4% for a sample concentration of 230 ng/mL, and to 6.7% for 3 ng/mL. The minimum detectable amount was below 1 ng/mL.