LC-MS Determination of Caffeine and Its Major Metabolite in Fingerprint Sweat

LC-MS was applied to the determination of caffeine and its major metabolite paraxanthine in fingerprint sweat. Fingerprint sweat was extracted ultrasonically with methanol from wet filter paper for 3 min at 35 ℃. Thermo Gold ODS C18 column was used as stationary phase,and a mixture of methanol and acetic acid (0.2+99.8) solution (65+35) was used as mobile phase. Positive electrospray ionization was used in the detection. Linear relationships between values of peak area and concentration of caffeine and paraxanthine were kept in definite ranges,with detection limits (3S/N) of 0.3,1.7 ng·片-1,respectively. Values of recovery found by standard addition method were in the range of 65.5%-71.3%,and values of RSD′s in the range of 3.3%-14%. Caffeine in fingerprint sweat could be detected from 1 h to 14 h after taking caffeine,and paraxanthine could be detected from 3 h to 14 h.