are shown below and are intended to assess performance as well as progress
of the student or worker. Some of the problems shown below are multi-level
in that the solution to one problem will lead to another question, simulating
the experience that a technician might encounter when working with actual
Problem 1. A technician
must determine p-xylene in a mixture of xylene isomers dissolved in methanol.
She has available a GC with a packed column and FID, as well as a GC/MS with
a capillary column. What instrument should she use for the analysis? What
injector, column, and detector temperatures should be used?
to see the correct answer.
Problem 2. An organic analysis
laboratory must determine the concentration of iodoacetone in river water.
A 100.0-mL sample of river water is mixed with 10.00-mL of MIBK (methyl-isobutyl
ketone) in a separatory funnel and shaken. This extracts all the iodoacetone
into the MIBK, which is then separated from the water sample. A standard solution
containing 1.0 x 10-7 M iodoacetone and 2.0 x 10-7 M p-dichlorobenzene (the
internal standard) is run on a gas chromatograph and gave peak areas of 400
and 800, respectively. The 10.00 mL sample of MIBK containing the iodoacetone
was treated with 0.100 mL of 2.0 x 10-5 M p-dichlorobenzene, equilibrated,
and the mixture was diluted to 20.00 mL. Analysis of the sample was to be
done the next day. Unfortunately, the laboratory technician had a hot date
and in haste, left the 20.00-mL mixture uncapped. Overnight the mixture evaporated
so that when the GC was run in the morning, the sample actually had a total
volume of 15.0 mL. The GC measurements gave peak areas of 700 and 500 for
iodoacetone and p-dichlorobenzene, respectively. Find the concentration of
iodoacetone in the original water sample. Did the technician's blunder have
any affect on the final results? Why or why not?
Problem 3. List the steps
and precautions that you should take when installing a new capillary column
in a gas chromatograph.
Problem 4. Why are test
mixtures important? Suggest the types of test mixtures that you should have
on hand in your laboratory?
to Skill Development Module L6.13 Gas Chromatograpy Introduction