Chem 213
Determination of Caffeine by HPLC
Instructions for Lab Report- part-A
Due Date : July 11th
A. Please write your name, date, course, lab section, objective of today’s experiment (part A), and
a brief but concise description of method (1-2 sentences).
B. Optimization of mobile phase composition: Attached are two 14-minutes HPLC runs (50-50 and
30-70 methanol-water compositions) of a caffeine and theophylline sample. Prepare a table
with the following data:
1) Mobile phase compositions, 2) Adjusted retention times (tR- tM) (assuming tM as 0.15 min in
both cases) of caffeine and theophylline, 3) Capacity factors (k’) for both, 4) separation factor
N
(γ − 1)
(γ), and 5) approximate resolutions (RS) using RS =
4
C. Calibration curve: Prepare a table of peak areas for your standards and your samples, and
produce a calibration curve using MS Excel. Remember to mark (with 3 sig fig) and label the
axes. Please paste the equation to the fitted straight line. Please include the actual variables (not
x or y), constants (not m or b) and their units. Attach your calibration curve to your report.
D. Determine the concentration of caffeine in your sample using the calibration curve. Correct for
dilutions you made for your sample and report it for the undiluted beverage sample. Please
give a sample calculation. Finally, report the average caffeine concentration (in ppm) and the
standard deviation in the original sample.
Problems:
Ch. 23: 18, 43