Most interesting equipment

Posted: Sun Jun 13, 2004 7:11 am

Equipment Notes:

Gas chromatograph
The gas chromatograph is basically a very fancy oven with a long glass tube sticking through it. The glass tube is rolled into a coil in order to get a longer tube into a pretty small space.

To better understand how a gas chromatograph works, it is useful to understand chromatography in general: chromato – light; graphy – mapping.

Doing the following activity is a simple way to see liquid chromatography in action.
1. Cut a paper towel into strips about 10 cm (5 inches) long.
2. Use a toothpick or pencil to poke a small hole at one end of strip. Thread the toothpick or pencil through the holes.
3. At the other end of the strip about 3 cm from the bottom, draw a horizontal line with a water-based marker (or with a Q-tip dipped in food coloring)
4. Fill a tall glass or cup with enough water so that the paper towel just barely touches the top of the water.
5. Hang the strip over the glass so that ONLY the tip of the strip touches the water. Take care to prevent the strip from touching the walls of the glass and the colored line from touching the water.
6. Wait for 15 – 30 minutes.
After some time, you will see the colors used to make up the marker or food coloring start to separate, pulled apart by the water rising through the paper towel.
7. If you want even more fun, try new colors, Kool-Aid crystals and Skittles.
8. If you are feeling sophisticated, use permanent markers and rubbing alcohol.

Liquids that are lighter are pulled up the chromatogram more easily than heavier liquids and so travel farther in the same amount of time.

In a gas chromatograph, a liquid is injected into the oven and heated up. Some parts of the liquid turn to gas (volatilize) faster than others so escape up the long glass tube faster than others. By measuring the type and amount of gas leaving the oven over a particular amount of time, we can infer what the liquid was made up of.

Interesting fact to make you smarter:
DNA samples are tested using the same principle, but use electricity to separate parts rather than gravity (liquid chromatography) or volatilization (gas chromatography).