# Calculating amount of caffeine from absorbance

The samples 75mL of coffee (Sample A) and tea (Sample B) were run. Determine the amount of caffeine/mL in a cup of tea or coffee and then the total amount of caffeine in a cup of 200mL.

Are there difference between the values at the two different wavelengths and why might this be the case? Explain the result: linear equation are r^2 for these standards

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#### Solution Preview

Absorbance at 270 nm for

y = 0.0407x and R^2 = 0.9934

Sample A: 1:200 dilution = 1ml of A in 200 mL of solution gives absorbance of 0.423

0.423 = 0.0407x

Hence x = 0.423 / 0.0407 =10.4 ug /ml. Hence, actual amount of A per ml of A = 10.4 ug x 200 = 2079 ug/ml = 2.08 mg /ml

Similarly for ...

#### Solution Summary

The amount of caffeine in an unknown is calculated from concentration vs absorbance curves.

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