AIR GC SEPARATION OF ALCOHOLS

Introduction:

The air GC is a gas chromatograph that uses air as the carrier gas. This eliminates the need for gas tanks and makes the instrument easier to move and set up. A gas chromatograph is an instrument that allows a chemist to separate a volatile mixture, identify the components, and measure the relative quantities of the components.

Purpose:

The purpose of this experiment is to determine the composition of an unknown alcohol mixture by using gas chromatography.

Equipment/Materials:

Air Gas chromatographvial of methanol
Computer with Peak Simple softwarevial of ethanol
Printervial of 1-propanol
All power cords and cablesUnknown samples of alcohol
10 microliter syringe

Safety:
-Always wear safety glasses in the lab

-Handle the syringes carefully. The syringes are very dangerous, especially when filled with hazardous chemicals. They also break easily. Do not allow the syringe to roll off of the lab bench. When injecting the sample, push the plunger straight so that it does not bend.

- The gas chromatograph is like an oven, so the port may be hot. Use caution.

Procedure:

1. Turn on the GC.

2.Start the Peak Sample software.

3.Set the following conditions from the edit menu by selecting channels then selecting channel 1 and temperature change.

Start 140°C
Hold 10 minutes
Ramp 0 degrees / min
Until the temperature is 140°C

4.Use the Z button on the run screen to zero the current.

5.Be sure the time scale starts at zero. Use the arrow to adjust.

6.Obtain a microliter syringe and a vial of a known alcohol standard.

7.Clean the syringe by rinsing it 3 times with this alcohol. With the plunger fully depressed, place the needle into the alcohol sample. Slowly draw up the plunger to obtain a sample of alcohol in the syringe. Remove the syringe from the alcohol sample. Discharge this sample into a waste container. Depress the plunger and put the syringe needle back into the alcohol sample. Draw up a second sample and discharge it into a waste container. Repeat for a third sample.

8.Place the syringe needle back into the alcohol sample and obtain 2 microliters of the standard alcohol. Wipe the needle with a Kimwipe.

9.Insert the needle carefully into the injection port of the GC until the needle stops.

10. Inject the sample and start the data collection simultaneously by depressing the syringe plunger and pressing the space bar on the computer at the same time.

11. If the sample peak returns to baseline, the run may be stopped by pressing the end button on the computer.

12.After the peak is obtained, record data or print the graph as instructed.

13.Repeat steps 7-12 for the other 2 known alcohols and the unknown alcohol. When running an unknown sample, be certain to let the data collect long enough to get all possible peaks.

Name______

Name______

Period______

Date______

AIR GC SEPARATION OF ALCOHOLS

DATA TABLE

Starting temperature
Holding time
Ramping rate
Final temperature
Data collection duration
Standards / Retention time
Methanol
Ethanol
1-propanol

Unknown number______

Calculations:

1.Calculate the area of each peak in the unknown. Treat each peak as a triangle to find its area. Find the total area by summing the areas of the individual peaks.

Component / Area
Methanol
Ethanol
1-propanol
Total
Unknown Sample / Retention Time / Identity of Peak
Peak 1
Peak 2
Peak 3

2. Calculate the percentage of each component in the unknown. Area of alcohol

% alcohol=Total Area

Questions:
1. Why was it important to run known sample of possible components in the unknown mixture?

2. If a supposedly pure sample was properly injected into the gas chromatograph and several peaks were observed, what can be concluded about the sample?

3.Why is it important to clean the syringe between samples?

4.Why is it important to wipe the needle before injecting the sample into the instrument?

Component / Percent
Methanol
Ethanol
1-propanol

AIR GC SEPARATION OF ALCOHOLS TEACHER NOTES

Lab Time:45 minutes

Answers to Question:

1.1. Why was it important to run known samples of possible components in the unknown mixture?

This was necessary to determine the retention times in order to identify the components in the unknown mixture.

2. If a supposedly pure sample was properly injected into the gas chromatograph and several peaks were observed, what can be concluded about the sample?

It contained some volatile impurities.

3. Why is it important to clean the syringe between samples?
Any trace of the previous substance will be detected by the gas chromatograph and produce an additional peak.

Science in Motion

Materials List

Lab: Air GC Separation of Alcohols

Number of Lab Groups Prepared:

Equipment per lab group / Delivered / Returned
Air Gas Chromatograph
Computer with Peak Simple
Software
Printer
2 Power Cords
Syringe for GC
2 Serial Cables
Goggles
(2) 25 ml, Beakers
Consumables / Delivered
Vial of methanol
Vial of ethanol
Vial of 1- propanol
Unmarked samples of alcohol
Vial of acetone
Vial of 2- propanol
Kim Wipes
Isopropenyl Alcohol