|Use:||Gas chromatography is used separate volatile organic compounds. When used in
combination with a detector, Gas Chromatography can be used to identify compounds.
See 9.1.1 for use with explosives.
Gas chromatography (GC) consists of four basic components:
- Either a direct injection or purge and trap method is used for sample introduction.
- Separation of a gaseous mixture is accomplished by using an unreactive carrier gas (mobile phase) such as nitrogen or helium to drive the mixture though GC column coated with nonvolatile liquid or solid sorbent (stationary phase). Because the components of the mixture interact to different extents with the stationary phase, they move along the column at different rates causing separation to occur.
- Once the analytes have been separated in the column, they are eluted one after another, and then enter a detector attached to the column exit.
- A method of quantifying identified compounds.
Detector selection depends on the compounds being analyzed:
|Thermal conductivity (TCD):||Gas analysis or sample. Detects oxygen, nitrogen, water, and other nonhydrocarbons to which other more sensitive detectors may not respond.|
|Flame-ionization (FID):||Virtually all hydrocarbon-containing molecules. Commonly used for analysis of PAHs, TPHs, and phenols.|
|Electron Capture (ECD):||Chlorinated, fluorinated, or brominated compounds including carbon-tetrachloride, PCBs, and pesticides.|
|Argon-ionization (AID):||Aliphatics, aromatics, halomethanes, and haloethanes.|
|Photo ionization (PID):||Aromatic molecules such as benzene, toluene, and xylene.|
|Electrolytic conductivity (ELCD):||Halogenated and sulfur compounds.|
|Flame photometric (FPD):||Sulfur gas analysis and organo-phosphate pesticides.|
|1. Non-Halogenated VOCs||4. Halogenated SVOCs||11. TPHs|
|2. Non-Halogenated SVOCs||5. PAHs|
|3. Halogenated VOCs||6. Pesticides/Herbicides|
|Requires extraction to liquid or gas phase||Requires extraction to liquid or gas phase||BETTER|
|Selectivity:||Technique measures the specific contaminant directly. GC has very good specificity, depending on the detector used, with excellent ability to resolve most components in very complex mixtures.|
|Susceptibility to Interference:||Low.|
|Detection Limits :||100-1000 ppb (soil); 1-50 ppb (water).|
|Turnaround Time per Sample:||Hours.|
|D 5790 - 95||Measurement of Purgeable Organic Compounds in Water by Capillary Column GC/MS.|
(Multiple ASTM Standards exist for specific contaminants in a variety of matrices).
|Series 8000||13 methods for specific analytes and detectors.|
|Series 8100||6 methods for specific analytes and detectors.|
|Series 500 and 510||9 methods for specific analytes (drinking water analysis).|
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