Levels of Organization Image Map
Step 4 continued: Separate and Purify

Gas Chromatography - Method 2

Another kind of chromatography is called "gas" chromatography. Note the diagram on the right. The cell chemicals are injected onto a heated column. The column may be many feet long and coiled so that you have a huge surface area for adsorption of dissolved substances. A gas (usually helium) carries the substances through the column, where they pass by an electronic detector at different rates.
  Gas chromatograph instrument. Door opens to the oven, which contains the coiled metal column. Injection port for samples is on top right of the cabinet, above the electronic control panel. Flow of carrier gas is fed in through the back.
 
What causes the dissolved particles to separate?


Because different chemicals have differentGC.chromatogram.jpg (105043 bytes)
adsorption properties, they separate over time. One chemical, for example, that does not stick well to the column will rush right through and the detector produces a spike in a graph to reveal its presence. Then, at later times other more sticky solutes will come off the column and produce delayed peaks. The tracing of the various peaks is called a chromatogram. If you carefully time when the peaks occur, you can actually collect the solutes at the other end.

Gas chromatography is not very useful for proteins. Know why? It is the heat, which denatures and destroys proteins.