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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
Determine the caffeine content, in ppm, of soft drink A.
Answer
To find the caffeine content in ppm for soft drink A, we refer to the calibration graph provided. The peak area for soft drink A is 12000. Looking at the calibration graph, we can determine that a peak area corresponding to 12000 corresponds to approximately 60 ppm concentration of caffeine. Thus, the caffeine content of soft drink A is approximately 60 ppm.
Step 2
What evidence is presented in the chromatogram that supports the conclusion that soft drink B does not contain any caffeine?
Answer
In the chromatogram for soft drink B, the major peak appears at a retention time of 32 seconds, which does not align with the retention time of caffeine, which is consistently recorded at 96 seconds in the calibration graph. This significant difference in retention time indicates that the peak observed in soft drink B is not due to caffeine, supporting the conclusion that soft drink B does not contain caffeine.
Step 3
Explain why the caffeine content of the espresso coffee sample cannot be reliably determined using the information provided.
Answer
The caffeine peak area for espresso coffee at 211000 exceeds the range of the calibration graph, which goes up to 200 ppm. Since the peak area of espresso coffee is outside the calibration range, we cannot accurately extrapolate or determine the exact caffeine concentration from this data, leading to potentially unreliable results.
Step 4
Describe what could be done to the espresso coffee sample so that its caffeine content can be reliably determined.
Answer
To accurately determine the caffeine content, the espresso coffee sample should be diluted to bring the caffeine concentration within the calibration range. For instance, a dilution factor that reduces the peak area into the range of the calibration curve (e.g., 1:10 or similar) can be applied. This will ensure that the peak area falls within a measurable range, allowing for reliable determination of caffeine concentration using the established calibration graph.