Quantification of caffeine by off-line TLC-MS

TLC-MS, more specifically TLC-SPE-APCI-MS, has been evaluated for determina tion of caffeine in soft drinks. Caffeine standards (between 1.0 and 20 mug spot(-1)) and samples of different soft drinks were applied to TLC plates, and the components were separated, and quantified by densitometry with ima ge analysis. After the in-situ evaluation, spots were marked and stationary phase containing the compounds was scraped from the plates, transferred to SPE cartridges, and eluted by use of solid-phase extraction (SPE) equipmen t. The substance was diluted one-hundredfold during the elution procedure; the eluted samples (10 muL) were injected into an LCQ-MSn spectrometer equi pped with an atmospheric-pressure chemical ionization (APCI) interface. The TLC-SPE-APCI-MS analytical procedure was validated and the limit of detect ion, limit of quantitation, precision, recovery, and linearity were evaluat ed. MS and MS-MS spectra of caffeine were obtained by direct injection of s tandards into the spectrometer. Results from validation showed the proposed off-line TLC-MS combination to be sensitive and repeatable. Acceptable MS and MS-MS spectra were obtained from 20 ng caffeine.