Gas Chromatography
Gas Chromatography (GC) is an analytical tool used to identify and quantitate a wide variety of compounds in a mixture. GC utilizes a compound’s intrinsic affinity for a “stationary phase” (solid support with specialized coating) and facilitates the separation of complex sample matrices into their component parts.
Essentially, in Gas Chromatography, a sample is injected into the hot inlet of a gas chromatogram, which volatilizes the components in the sample. Next, an inert gas (“carrier gas”) carries the volatile compounds through a coated capillary column. The capillary coating or “stationary phase” is housed inside the capillary column. The flame ionization detector (FID) passes sample and “carrier gas” from the column through a hydrogen-air flame. The hydrogen-air flame alone creates few ions, but when an organic compound is burned, there is an increase in ions produced. A polarizing voltage attracts these ions to a collector located near the flame. The current produced is proportional to the amount of sample being burned.
![GC](https://www.atomicecho.com/wp-content/uploads/2023/06/GC-1024x789.jpg)
This current is sensed by an electrometer, converted to digital form, and sent to a data system where a chromatogram is electronically constructed. The time it takes a specific compound to pass through the capillary column and to a detector is called its “retention time.” Retention time, which is inherently related to a compound’s affinity to the stationary phase, can be used to identify the compound in question when compared to a reference standard.
Ideal Uses of Gas Chromatography
- Quantitative volatile analysis
- Purity profile quantitation
- Residual solvents quantitation
Strengths
- GC/FID is sensitive to virtually all compounds that contain hydrocarbons and that will burn; examples are aromatic and chlorinated VOCs, petroleum constituents, SVOCs and PCBs
Limitations
- Samples must either be volatile or capable of derivatization
- GC/FID is responsive to compounds with carbon-hydrogen bonds only
- GC/FID is a destructive technique so no additional analysis can occur on the sample after it is performed
- Identification and quantitation is limited to the compounds for which reference standards are run
GC Technical Specifications
- Detection limit “on column”:
- Approximately 1 ppm (Direct Injection)
- Approximately 10 ppb (Headspace Injection)
- Suitable operating temperature for chromatographic separations: 30-450°C