The cartridges were conditioned using 2 ml of methanol and 2 ml of
deionized water, and then loaded with 1 ml of blood. Analytes were eluted with
3 ml of n-hexane; the eluate was then evaporated to dryness. The dry extract was
dissolved in hexane spiked with internal standard. In the final step, 1 ml was
injected into the GC/MS system.