gas-liquid chromatography

Chromatography {gas-liquid chromatography} (GLC) can use stationary liquid phase and moving gas phase.

purpose

GLC can separate high-volatility substances, such as molecules with carbon, nitrogen, and hydrogen atoms, and determine amounts, with no decomposition. GLC needs only small sample.

process: column

Columns are polyester, silicone polymer, or diatomaceous earth, with varying mesh sizes. Mesh size determines surface area. Columns are 1 to 3 meters long.

process: solvent

Solvent saturates column material. Inert, thermally stable liquids with low vapor pressure can be solvents. Typical solvents are naphthalene or anthracene. Squalene is for non-polar molecules. Amides are for polar molecules.

process: solution

Solution starts at column end.

process: gas

Inert helium or nitrogen gas, at high pressure, is mobile phase.

process: flow

Volatile molecules in solution can separate between gas and liquid phases. More-volatile molecules spend more time in moving gas phase and move faster. High flow-rate minimizes diffusion. Heating makes molecules more volatile. Temperature is 25 C to 150 C. Lower temperature gives better resolution.

volume

Gas volumes {retention volume} elute samples.

time

Columns take time {retention time, column} to elute samples. Retention time depends on number of carbons. Bigger molecules are slower. First sample takes minimum time {dead time}.

detection

To detect sample, use Wheatstone bridge to measure conduction {thermal conductivity} (TCD).

Ionize in flame {flame ionization} (FID), if sample is solid or liquid organic but not carbonyl.

Measure decrease in electron flow {electron capture} (ECD) for halogens, oxygen, nitrogen, and sulfur compounds but not for hydrocarbons, amines, or ketones.

Whole Section in One File

5-Chemistry-Analytical Chemistry-Chromatography-Kinds

Drawings

Technical Information

Date Modified: 2022.0224