Chemistry 210 Experiment 4

Experiment 4

Chromatography 2: Gas Chromatography

Reading (in Zubrick): Ch 31 (all)

Outline: Determine the percent composition of a mixture of organic compounds

Background/Procedure

We will use a gas chromatograph (GC) with a thermal conductivity detector (TCD) for this experiment. You do not need to worry about controlling any parameters, such as helium flow rate, column temperature, injector temperature, or TCD settings – the chromatograph and integrator will do all of this for you. Also, you will print out information about the analyzed peaks, which will include the integration value (peak area) for each peak (corresponding to each hydrocarbon), so you won't need to calculate this value either.

You will run each of the following three hydrocarbons individually: toluene, methyl acetate and cyclohexane. Then, you will analyze a mixture of these three hydrocarbons of known concentration which is made by combining equal amounts of these three compounds (1:1:1 by volume). You will also create a chromatogram of mixture of the same chemicals but at unknown concentrations. You will need to compare the peak areas from the unknown mixture to those in the known mixture to determine the percent composition of the unknown mixture.

Safety: Toluene, methyl acetate and cyclohexane are all toxic, irritants, and flammable liquids – wear gloves while handling them, and no flames are allowed in the class.

Using the Chromatograph

We will be using two chromatographs, both of which are Shimadzu GC-14A's. For convenience (and at the whim of your instructor) they have been named, "Bob" and "Ray". Each one is fitted with a thermal conductivity detector (TCD; also known as a "hot wire" detector). Each one has a 10-foot column with a 1/8" bore; the liquid phase is Supelco 10% SP-2100 (a relatively non-polar liquid phase). The chromatographs will be pre-set with these parameters:

Column Temp: 75 °C
Injector Temp: 160 °C
Detector Temp: 200 °C
Carrier gas (He) flow rate: ~30-35 mL/min.

Each group of two people will use either Bob or Ray – it is important to record in your notebook which one you use. Perform the following procedure for each sample:

Use a 10 μL syringe to measure about 0.5-1 μL of the organic solvent, or mixture of solvents for injection into the TCD sample port (this port, which is hot, and is the one on the right).
Carefully insert the tip of the syringe needle into the TCD sample injector port, and gently push the syringe all the way in, but without pressing the plunger too hard. (You should practice using the syringe, without bending the plunger).
One partner presses the plunger all the way in and the other partner presses the "Start 1/Stop" button on the integrator at exactly the same time (do not press any other button).
Leave the syringe inserted into the injector for about 5 seconds, then remove it.
Wait until all three peaks (of single peaks if you are running only one chemical) are recorded by the integrator, plus about one minute. (Total chromotography time may exceed 6 minutes. Make certain the number of peaks you are expecting have been recorded.)
After all peaks have been recorded, press the "Start 1/Stop" button again.
Wait for the integrator to stop printing. If you are going to run another sample, inject the sample and record the chromatogram.
If you are through running the GC, press the "Feed" button to advance the paper. When it has gone far enough, press the "Feed" button again to stop it. Tear off your chromatogram. Be sure to label your chromatograms with the sample name, the name of the chromatograph, and the names of the people in your group.

PREPARATION FOR THE NEXT LAB, EXPERIMENT V

Preparation for Experiment V Fermentation: During Experiment V you will do a distillation of ethanol from a fermentation mixture. You will prepare your own fermentation mixture but you must start the fermentation during the second day of Experiment IV in order to allow the one week period for this fermentation to take place. Please look at the protocol for Experiment V to see how this fermentation mixtures is to be set up. Remember, it must be done on the last day of this experiment in order to let the fermentation proceed for one week.

Go To Experiment: VSEPR 1a 1b 1c 2 3 4 5 6 7 8 9 10
Return to Chem210 Experiments Index