Assessment tools 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 instrumentation.
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?
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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?
Return to Skill Development Module L6.13 Gas Chromatograpy Introduction