Calibration curves for caffeine and GA were constructed. Aliquots (0.20–2.40 μL) of caffeine stock solutions (l.00 mg/mL) were applied directly to TLC plates as described giving a final concentration of 0.20–2.40 μg/band. For GA, a set of standard solutions (50.0–500.0 μg/mL) was prepared. Equal aliquots from each solution were spiked and properly mixed with 0.5 mL of decaffeinated extract. Aliquots of 20 μL of each spiked solution were applied to TLC plates, giving a final concentration range of 0.50–5.00 μg/band. Development and scanning were carried out as described above. The peak area was recorded and calibration curves were constructed by plotting the integrated peak area versus the corresponding concentrations and regression equation parameters were computed. The assay for both caffeine and GA were validated according to ICH guidelines ( ICH guidelines: Validation of analytical procedures, 2005).