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Caffeine is a stimulant drug that is found in coffee, tea, energy drinks and some soft drinks - VCE - SSCE Chemistry - Question 3 - 2011 - Paper 1
Question 3
Caffeine is a stimulant drug that is found in coffee, tea, energy drinks and some soft drinks. The concentration of caffeine in drinks can be determined using HPLC. ... show full transcript
Worked Solution & Example Answer:Caffeine is a stimulant drug that is found in coffee, tea, energy drinks and some soft drinks - VCE - SSCE Chemistry - Question 3 - 2011 - Paper 1
Step 1
a. Determine the caffeine content, in ppm, of soft drink A.
Answer
To find the caffeine content of soft drink A, we utilize the calibration graph that correlates the peak area to caffeine concentration.
From the results presented, soft drink A has a peak area of 12000. By examining the calibration graph, we notice that a peak area of 12000 corresponds to a caffeine concentration of approximately 60 ppm. Therefore, the caffeine content of soft drink A is
Caffeine content of soft drink A = 60 ppm.
Step 2
b. What evidence is presented in the chromatogram that supports the conclusion that soft drink B does not contain any caffeine?
Answer
The chromatogram for soft drink B shows that there is no significant peak at the retention time of 96 seconds, which is the retention time for caffeine based on the calibration graph.
Since a caffeine peak is absent, this directly indicates that soft drink B does not contain caffeine.
Step 3
c. i. Explain why the caffeine content of the espresso coffee sample cannot be reliably determined using the information provided.
Answer
The caffeine content of espresso coffee cannot be reliably determined because the peak area (211000) for espresso coffee significantly exceeds the upper range of the calibration curve, which was constructed using standard solutions with a maximum of 200 ppm.
This means we cannot extrapolate the concentration accurately beyond the provided range.
Step 4
c. ii. Describe what could be done to the espresso coffee sample so that its caffeine content can be reliably determined.
Answer
To determine the caffeine content of the espresso coffee sample reliably, one approach would be to dilute the espresso coffee sample until the caffeine concentration falls within the established range of the calibration curve.
For instance, by diluting with a suitable solvent, you could bring the concentration of caffeine down below 200 ppm. Following this dilution, the diluted sample can be analyzed to measure its peak area, which can subsequently be compared against the calibration graph to find the corresponding caffeine concentration.