A rapid sensitive method for serum caffeine analysis is reported. One hundred microliters of serum is mixed with 50 microliters of the acetonitrile/internal standard mixture, centrifuged, and 10 microliters of the supernatant is injected into the liquid chromatograph. Caffeine and internal standard are eluted at 6.09 and 7.17 minutes respectively. The procedure is linear to at least 20 micrograms/milliliter. The within run precision was 2.3 and 3.8 (N=10) respectively for mean concentrations of 7.77 and 15.73 micrograms/milliter. Between day precision was 11.0 and 8.6 respectively for mean concentrations of 7.63 and 15.55 micrograms/milliliter. Recovery of caffeine over the analytical range averaged 104.
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