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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 determine the caffeine content of soft drink A, we will utilize the calibration graph and the peak area data provided. The peak area for soft drink A is 12000 (×1000). From the calibration graph, we identify the corresponding caffeine concentration for this peak area.
Assuming a linear relationship between peak area and caffeine concentration from the calibration graph, we can read the concentration at a peak area of 12000, which approximates to 50 ppm. Therefore, the caffeine content of soft drink A is approximately 50 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 no significant peak at the retention time of 96 seconds, which is the expected retention time for caffeine. The absence of a peak indicates that soft drink B does not contain caffeine, as there is no detectable concentration in the sample analyzed.
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 the espresso coffee sample cannot be reliably determined because the peak area measurement of 211000 exceeds the range of the calibration curve, which only goes up to 200 ppm. Since it is outside the established range, we cannot accurately extrapolate the caffeine concentration from the peak area.
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 reliably determine the caffeine content of the espresso coffee sample, we should dilute the sample. This would lower the peak area and bring it within the range of the calibration curve. For instance, diluting the espresso coffee sample to obtain a peak area that corresponds to a known concentration on the calibration curve will allow for accurate determination of the caffeine content.