High-throughput determination of theophylline and caffeine in human serum by conventional liquid chromatography-mass spectrometry

Automated high-performance liquid chromatography/mass spectrometry (HPLC-MS) with backflush column-switching was established for ultra-fast determination of theophylline and caffeine. A 400-μl portion of serum sample diluted with ultrapure water was injected and transferred to an Oasis HLB cartridge used as a precolumn for extraction. After switching the valves, the analytes trapped in the precolumn were eluted in the backflush mode and separated with a Chromolith Performance RP-18e column (C₁₈-bonded monolithic silica); the compounds in column effluents were then detected by atmospheric pressure chemical ionization (APCI)-MS. The present method successfully provided high-throughput determination of theophylline and caffeine within 2 min. Satisfactory linearity, reproducibility, and sensitivity could be obtained for analysis of therapeutic and toxic levels of both compounds. Because of the very simple procedure and high throughput using the conventional HPLC system, the present method seems to have high potential in the fields of forensic toxicology and emergency medicine.