Reference no: EM133142013
SMA0020 Practical - Determination of the relative proportions of caffeine and aspirin by GC-MS
The purpose of this experiment is to determine the concentration of caffeine and ethyl-2-acetoxybenzoate (aspirin derivative) contained in the solution provided. A calibration curve will be constructed using standards, then the unknown sample will be measured and its caffeine and ethyl-2-acetoxybenzoate content calculated.
Your graphs (drawn in Excel or a similar program) and your chromatograms must be attached to your report.
Part 1 - Calibration curve
Run each standard solution once, starting with the lowest concentration. Record your measurements in the table below and plot separate calibration graphs for peak area and peak height vs. concentration for each standard (four graphs in total).
Caffeine:
|
Conc/ppm
|
Mean Peak area
|
Mean Peak height
|
|
50
|
|
|
|
100
|
|
|
|
150
|
|
|
|
200
|
|
|
|
250
|
|
|
Ethyl-2-acetoxybenzoate:
|
Conc/ppm
|
Mean Peak area
|
Mean Peak height
|
|
50
|
|
|
|
100
|
|
|
|
150
|
|
|
|
200
|
|
|
|
250
|
|
|
Part 2 - Analysis of unknown solution
Record the peak areas and peak heights for the unknown sample in triplicate.
Caffeine:
|
Injection
|
Peak area
|
Peak height
|
|
1
|
|
|
|
2
|
|
|
|
3
|
|
|
|
Average
|
|
|
|
SD
|
|
|
Ethyl-2-acetoxybenzoate:
|
Injection
|
Peak area
|
Peak height
|
|
1
|
|
|
|
2
|
|
|
|
3
|
|
|
|
Average
|
|
|
|
SD
|
|
|
Calculate the concentration of caffeine and ethyl-2-acetoxybenzoate in the unknown solution, including an error value:
|
Caffeine content of unknown solution =
|
Error =
|
|
Ethyl-2-acetoxybenzoate content of unknown solution =
|
Error =
|
Questions -
1. Why are calibration standards always analysed in increasing order of concentration?
2. Comment on the linearity of your calibration graphs.
3. Comment on the magnitude of the errors in your measurements of the unknown concentration.