AC3 TEMPERATURE PROGRAMMING IN GAS CHROMATGRAPHY Last Revised:
May 2014
1. PURPOSE This exercise covers the optimisation of conditions to maximise the efficiency of separation of different mixtures. 2. REAGENTS & EQUIPMENT 2.1 Gas chromatograph and column suitable for separation of mixed alkanols 2.2 Mixture of methanol, ethanol, 1‐propanol and 1‐heptanol (MEPH) 2.3 Complex mixture 2.4 1 L syringe 3. PROCEDURE 3A. Instrumental setup 3.1 Record the following information:  column type  column internal diameter  column length  maximum operating temperature  flow rate 3.2 Observe the startup procedure for the instrument. 3B. Separation SAMPLE MEPH 3.3
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Inject sample MEPH at 75, 150C and one other temperature which you consider useful. Discuss with your teacher what needs to be done to improve the separations. Consider whether you need to use temperature programming. It is not essential that all peaks be totally resolved. Accurate peak area integration can occur with overlap of less than 20% peak height. Devise a suitable temperature program to improve the separation for each sample. Discuss it with your teacher. Adjust the controlling software to allow this program to be used. Record the chromatogram using your temperature program. Make appropriate modifications to maximise the efficiency of the separation. 3.6
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COMPLEX MIXTURE 3.9 The complex mixture will have the number of components indicated. You must design a temperature program that achieves satisfactory and efficient separation of all components. 4. REPORT Calculations The following need only be done for the runs on sample MEPH. No calculations are required for the complex mix. 1.
Tabulate the retention times for each compound from each isothermal run. 2.
Plot a single graph of retention time against temperature (for the three isothermal runs) for each of the alkanols 3.
Calculate the value of N for the column, using all well‐shaped peaks. The computer printout gives the value of peak width (in minutes). 4.
Calculate the average value of N, disregarding any low values. 5.
Calculate the number of plates per metre, using the average value of N. 6.
Calculate the resolution (R) value for any peaks that are not completely resolved. Discussion 
for each sample, discuss how each change to the temperature conditions affected the separation 
compare the column performance (in terms of N per metre) to the expected value 
list the column characteristics (i.e. dimensions) Questions 1.
Why is temperature programming necessary for samples such as those in this exercise? 2.
Why are capillary columns more efficient at separation than packed columns? AC3 p2