Experiment 4

Background/Procedure

Reading (in Zubrick): Ch 31 (all)

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

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 cyclohexanone. 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 cyclohexanone 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 Agilent Technologies 6890N GCs. For convenience (and at the whim of your instructor) they have been named, "Ben" and "Sean". Each one is fitted with a flame ionization detector (FID). Each GC one has a 30 meter Supelco supelcowax fused silica capillary chromatography column with a 250 μm x 0.25 nominal. The chromatographs will be pre-set with these parameters:

Column Temp: 150 °C
Injector Temp: 250 °C
Detector Temp: 250 °C
Carrier gas (He) flow rate: ~2 mL/min.

Each group of two people (or two groups together consisting of four students) will use either Ben or Sean – it is important to record in your notebook which one you use. Perform the following procedure for each sample, as described below:

1. Pick up one copy each of the GC handout titled "Chem210 Exp 4 GC knowns," which contains an chromatogram of each sample run individually and all three run together (compare the retention times for each individual sample with the corresponding sample in the chromatogram with all three chemicals).
2. Select any two of the unknown samples (A, B, C, D, E, F, G, H, or I) for your analysis.
3. Write down both the name of the GC and the letters of your unknown samples.
4. Sit down or stand around the GC you will be using.
5. The screen will have a bright green arrow at the top left corner of the screen.
6. Wait for the "Start Run" screen to pop up.
7. Select the "OK and Run" box at the bottom of the screen.
8. Wait for your two runs to finish.

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.