The determination of 11-nor-delta9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) in hair using negative ion gas chromatography-mass spectrometry and high-volume injection.

The determination of 11-nor-delta9-THC-9-carboxylic acid (THC-COOH) in hair specimens at the sensitivity required to detect marijuana users is a difficult analytical problem. A sensitive and specific method has been developed for the quantitative assay of THC-COOH in hair. Hair specimens were washed, incubated in sodium hydroxide, subjected to solid-phase extraction, and analyzed using high-volume injection coupled with negative chemical ionization (NCI) mass spectrometry. A common disadvantage of chemical ionization, the production of a single mass-to-charge ratio ion, was also addressed. By specific selection of the derivatizing agent, three ions were monitored, allowing the calculation of two ion ratios, as in electron impact mode. The method was applied to several hair specimens taken from known marijuana users and workplace specimens. This is the first publication describing the use of high-volume injection and NCI mass spectrometry for the determination of THC-COOH in hair.