Solid-Phase Extraction of Caffeine and Theophylline from Green Tea by a New Ionic Liquid-Modified Functional Polymer Sorbent

The new ionic liquid-modified polymer sorbent was developed by surface chemical modification of the synthesized polymer particles using ionic liquids. The obtained ionic liquid-modified polymer was successfully used as a special sorbent in a solid-phase extraction (SPE) process to isolate caffeine and theophylline from green tea. A comparison of different SPE cartridges using the blank polymer, C₁₈, and ionic liquid-modified polymer revealed that the highest recovery was obtained using ionic liquid-modified polymer sorbent. Quantitative analysis was carried out by using a C₁₈ column (5 µm, 150 × 4.6 mm) as an analytical column. Good linearity was obtained from 5 × 10^?4 to 0.5 mg/mL (r²>0.999) for the two analytes with relative standard deviations <4.5%.