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| Typical Number in Hospital: 3 | Cost Bands: 4 | References: 9 |
A sample of body fluid, usually blood, is purified to some extent and then added to an organic solvent before being flash vaporized and fed into a column of solid material (e.g. diatomaceous earth) which may be a few millimetres in diameter and 1 metre long. A carrier gas (usually nitrogen or helium) is also injected into the column which sweeps the evaporated sample down the column. A detector at the end of the column provides an electrical output proportional to the quantity of the compound found in the effluent gas. A number of types of detector are available which include ionization detectors, thermal conductivity detectors, and electron capture detectors. Ionization detectors are most commonly used in clinical laboratory applications. The electrical output is fed to a recorder which shows a number of peaks of output corresponding to particular materials, commonly drugs.
Gas-liquid chromatographs can work with very small samples with great sensitivity and produce complete analyses of important substances in less than one hour.
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