ALCOHOL MIXTURE COMPOSITION
Step 1
Correlate the two alcohol peaks on your chromatogram with the two peaks (out of five)
on the reference chromatogram provided to you.
To correlate, you need to match the retention times (RT) for your two alcohols with the
two alcohols on the reference chromatogram.
If you find it difficult to correlate directly, generate the following table to correlate the
two alcohol peaks on your chromatogram for the original mixture with the two alcohols
on the reference chromatogram.
Determine the time difference between solvent peak and alcohol peak in every case.
Note: The example given here is for a different set of alcohol standards and original
mixture.
Peaks
Time Difference
(Alcohol Peak – Solvent Peak)
Comment
Alcohol 1
1.220 – 0.970 = 0.250
-
Alcohol 2
1.367 – 0.970 = 0.397
-
Alcohol 3
2.166 – 0.970 = 1.196
-
Alcohol 4
3.370 – 0.970 = 2.400
-
Alcohol 5
4.085 – 0.970 = 3.115
-
Unknown Peak 1
1.238 – 0.974 = 0.26
Unknown Peak 2
4.360 – 0.974 = 3.38
Correlates to
Alcohol 1
Correlates to
Alcohol 5
Introducing correction factor for the standard alcohols
Let the arbitrarily assigned value for alcohol 2 is 1.00000.
Alcohol
RT
% Area
Alcohol 1 1.220
4.00484
Alcohol 2 1.367
3.71922
Alcohol 3 2.166
3.33272
Alcohol 4 3.370
3.91529
Alcohol 5 4.085
2.32067
Correction Factor
% Area for alcohol 2 / % Area for Alcohol 1
3.71922 / 4.00484 = 0.928681
% Area for alcohol 2 / % Area for Alcohol 2
3.71922 / 3.71922 = 1.000000
% Area for alcohol 2 / % Area for Alcohol 3
3.71922 / 3.33272 = 1.115971
% Area for alcohol 2 / % Area for Alcohol 4
3.71922 / 3.91529 = 0.949921
% Area for alcohol 2 / % Area for Alcohol 5
3.71922 / 2.32067 = 1.602649
Corrected
Factor
0.928681
1.000000
1.115971
0.949921
1.602649
% Peak area for the unknown alcohol peak 1 = 19.10450
% Peak area correction for Unknown Alcohol Peak 1 (which correlates alcohol 1)
19.10450 X 0.928681 = 17.74198
% Peak area for the unknown alcohol peak 2 = 36.64779
% Peak Area Correction for Unknown Alcohol Peak 2 (which correlates to alcohol 5)
36.64779 X 1.602649 = 58.73354
Therefore,
The percentage of each alcohol in the mixture:
Unknown Alcohol 1 =
17.74
--------------------- X 100 = 23.20 %
(17.74 + 58.73)
Unknown Alcohol 2 =
53.73
--------------------- X 100 = 76.80 %
(17.74 + 58.73)
Also, determine the percentage purity for the fractions collected
during fractional distillation by similar data analysis.