Micro-pulverized extraction pretreatment for highly sensitive analysis of 11-nor-9-carboxy-Δ(9)-tetrahydrocannabinol in hair by liquid chromatographytandem mass spectrometry.
A primary metabolite of Δ(9) -tetrahydrocannabinol, 11-nor-9-carboxytetrahydrocannabinol (THC-COOH), serves as an effective indicator for cannabis intake. According to the recommendations of the Society of Hair Testing, at least 0.2 pgmg of THC-COOH (cut-off level) must be present in a hair sample to constitute a positive result in a drug test. Typically, hair is digested with an alkaline solution and is subjected to gas chromatographytandem mass spectrometry (GCMSMS) with negative ion chemical ionization (NICI). It is difficult to quantify THC-COOH at the cut-off level using liquid chromatographytandem mass spectrometry (LCMSMS) without acquisition of second-generation product ions in triple quadrupole-ion trap mass spectrometers, because large amounts of matrix components in the low-mass range produced by digestion interfere with the THC-COOH peak. Using the typical pretreatment method (alkaline dissolution) and micro-pulverized extraction (MPE) with a stainless bullet, we compared the quantification of THC-COOH using GCMSMS and LCMSMS. MPE reduced the amount of matrix components in the low-mass range and enabled the quantification of THC-COOH at 0.2 pgmg using a conventional triple quadrupole liquid chromatograph coupled to a mass spectrometer. On the other hand, the MPE pretreatment was unsuitable for GCMSMS, probably due to matrix components in the high-mass range. The proper combination of pretreatments and instrumental analyses was shown to be important for detecting trace amounts of THC-COOH in hair. In MPE, samples can be prepared rapidly, and LCMSMS is readily available, unlike GCMSMS with NICI. The combination of MPE and LCMSMS might therefore be used in the initial screening for THC-COOH in hair prior to confirmatory analysis using GCMSMS with NICI.