Gas Chromatography

Pre lab Questions

A) Refer to the gas chromatograph (below) of a mixture of Compound A (RT = 1.11) and Compound B (RT=2.27), which was done on a general purpose column:

Which compound has the highest retention time?
Which compound is present in a larger amount assuming that their mass correction factors are equal?
Which compound has the lower boiling point?
What would happen to the retention times of compounds A and B if the column temperature were raised?

For questions B and C consult: http://chemconnections.llnl.gov/Organic/Chem226/Labs/GC/LiqPhases.htm

B) Consider the following compounds:

compound	boiling point
A) methyl cyclohexane	101
B) pentane	36
C) octane	126
D) 2,3-dimethyl octane	165
E) heptane	98

If the compounds in the table above are run on a GC column that has DC-710 as the stationary phase, rank the compounds in the order that they would be detected coming off of the column. C) Consider the following compounds:

compound	boiling point
A) propionic acid	141
B) 2-hexanol	140
C) isoamyl acetate	142
D) 3,4-dimethylheptane	140

If these compounds are run on a GC column that has DEGS as the stationary phase, rank the compounds in increasing order of retention times. D) You think that you injected your sample into the GC, but you see no peak after five minutes. So, you increase the data sampling period for another five minutes, but see nothing. You repeat this two more times but still see nothing.What should you do? (Ask Dr. R. is NOT a correct response.)

E) State the stationary and moving (mobile) phases in each type of chromatography below:

gas (GC)
thin layer (TLC)

F) Rank the following compounds in terms of their expected retention times on a GC column that has OV-101, a non polar material, as the stationary phase, and then rank them according to predicted order of R_f values on a silica gel TLC plate that is eluted with hexane as the solvent. (b.p. and m.p. = oC; d = g/mL)

I........................ II ..........................III ......................IV