In an estimation of caffeine from tea, using HPLC, the following results were obtained. A series of calibration standards, injected with a 10uL loop injector, gave the linear regression for the calibration line as S = 0.6352 c +0.3633, where c is the concentration in ppm of caffeine and S the area of caffeine signal.
A 5.0 gram sample of tea was extracted with 200 mL of boiling water for 2 minutes. Caffeine from 2.0 mL of the above tea, after solid phase extraction, was diluted to 50. mL with the mobile phase. 10uL of the sample extract upon injection gave an area for the caffeine peak of 12.0 units.
Calculate the amount (mg) of caffeine present in the 5 g tea.