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In this study, solid-phase extraction (SPE) is described using a novel fluorinated [heptadecafluorotetrahydrodecyl (C(10)H(4)F(17))] phase to isolate THC and its primary metabolite carboxy-THC from whole blood samples. SPE was performed in hydrophobic mode after samples of whole blood were precipitated with acetonitrile. After applying the sample to the SPE column in aqueous phosphate buffer (pH 7), the sorbent was washed with deionized water and phosphate buffer (pH 7) and dried. The SPE column was eluted with a solvent consisting of ethyl acetate/hexanes (50:50) containing 2% acetic acid. The eluate was collected, evaporated to dryness, and dissolved in mobile phase (50 microL) for analysis by fast liquid chromatography-tandem mass spectrometry in positive/negative multiple reaction monitoring mode. Chromatography was performed in gradient mode employing a C(18) column and a mobile phase consisting of acetontitrile (containing 0.1% formic acid) and 0.1% aqueous formic acid. The total run time for each analysis was less than 5 min. The limits of detection/quantification for this method were determined to be 0.1 and 0.25 ng/mL, respectively. The method was found to be linear from 0.25 to 50 ng/mL (r(2) >or= 0.995). Recoveries of the individual cannabinoids were found to be greater than 85%. In this report, results of authentic samples analyzed for THC and carboxy-THC are reported using this new methodology.