Gas chromatography is a technique used to separate volatile organic compounds. A gas chromatograph consists of a flowing mobile phase, an injection port, a separation column containing a stationary phase, and a detector. The organic compounds are separated due to differences in their partitioning behavior between the mobile gas phase and the stationary phase in the column. There are a number of types of detectors available for gas chromatographs: thermal conductivity, flame ionization, atomic emission, electron capture, photo ionization, flame photometric, chemiluminescence spectroscopy, and nitrogen phosphorous types of detectors. Each has its own unique characteristics that make it the ideal choice for a particular application.
One important specification is whether or not the column is to have a heater. If so, the heater can be isothermal or else can have temperature controls so the operator can program the temperature into the instrument. Gas chromatographs can have flow controls as integral features in their pumping units. An important specification for the pump is he inlet pressure range.
One important specification is whether or not the column is to have a heater. If so, the heater can be isothermal or else can have temperature controls so the operator can program the temperature into the instrument. Gas chromatographs can have flow controls as integral features in their pumping units. An important specification for the pump is he inlet pressure range.
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Last Updated: Sep 2009
Last Updated: Sep 2009
What are Gas Chromatographs?
Gas chromatographs can have multiple injection ports, either valve or syringe type. Methods of injection can be either split/splitless or packed column injection. With split/splitless column injection the injector has another set of gas lines out, which is another path that the vaporized sample can take. This extra line is called the split line or vent. The amount of gas that exits the split line controls the amount of sample that enters the column. With packed column injection, all samples enter the column, including the gaseous sample, the solvent, and the analyte. This may also be called a direct or flash injector.
User interfaces for gas chromatographs can be analog, with dials, switches and potentiometers; digital, with menus, keypads and buttons; or computer interfaces connected to the chromatographs by a serial or parallel or other connection. Displays can be analog meters, numeric or alphanumeric digital displays or video terminal. Outputs from gas chromatographs, aside from computer-readable data, can be analog voltage, current or frequency. Another option is to have the output be an alarm or change in state of switches.
Features that are available for some models of gas chromatographs are programmability and data storage options. Extreme environment ratings are available, as is the ability to handle liquid samples in addition to the gas sampling that the gas chromatographs were designed for.
User interfaces for gas chromatographs can be analog, with dials, switches and potentiometers; digital, with menus, keypads and buttons; or computer interfaces connected to the chromatographs by a serial or parallel or other connection. Displays can be analog meters, numeric or alphanumeric digital displays or video terminal. Outputs from gas chromatographs, aside from computer-readable data, can be analog voltage, current or frequency. Another option is to have the output be an alarm or change in state of switches.
Features that are available for some models of gas chromatographs are programmability and data storage options. Extreme environment ratings are available, as is the ability to handle liquid samples in addition to the gas sampling that the gas chromatographs were designed for.
