3. Apparatus
3.1 Sample Inlet Systems, represent the means for introducing samples into the separation column, including the heated zones permitting the vaporization of the introduced liquid samples prior to their passage through the column. Sample introduction can be carried out by introduction of a liquid, solid, or gas into the carrier-gas stream. The sample may be vaporized before or after introduction into the column.
3.1.1 Direct Inlets, rapidly vaporize the sample prior to entering the column. All of the sample vapor enters the column.
3.1.2 On-Column Inlets, introduce a liquid sample into the column. The sample vaporizes as the column section containing the liquid heats up after injection.
3.1.3 Split Inlets, rapidly vaporize the sample prior to entering the column. A defined fraction of the sample vapor enters the column; the remainder leaves the inlet through a vent at a flow rate Fv. The ratio of the total inlet flow (Fv + Fc) to the column flow ( Fc) is called the split ratio (s):
3.1.4 Splitless Injection, utilizes a split inlet wherein the split vent flow is blocked during the injection period such that most of the sample vapor enters the column. The injection period is typically one minute. The split vent flow is reestablished afterward usually for the remainder of the run.
3.1.5 Programmed-Temperature Vaporizers (PTV), accept a liquid sample that vaporizes as the inlet system heats up after injection. A PTV may operate in either a split, splitless, on-column, or direct mode.
3.1.6 A Retention Gap, is a section of tubing inserted between the inlet and the analytical column proper. The retention gap may have an inner diameter different than the analytical column. The retention gap has significantly lower retaining power than the analytical column; in practice the retention gap is deactivated but not coated.
3.2 Columns, consist of tubes that contain the stationary phase and through which the gaseous mobile phase flows.
3.2.1 Packed Columns, are filled with granular packing that is kept in place by gas-permeable plugs at both ends.
3.2.2 Open-Tubular Columns, have unobstructed central gasflow channels.
3.2.2.1 Wall-Coated Open-Tubular Columns, abbreviated WCOT columns, have the liquid phase coated directly on the inside, relatively smooth wall of the column tubing.
3.2.2.2 Porous-Layer Open-Tubular Columns, abbreviated PLOT columns, have a solid porous layer present on the tube wall but still maintain the unobstructed central gas-flow channel. This porous solid layer can either act as an adsorbent or a support which in turn is coated with a thin film of the liquid phase, or both. The solid layer can either be deposited on the inside tube wall or formed by chemical means from the wall.
3.2.2.3 Support-Coated Open-Tubular Columns, abbreviated SCOT columns, refer to those PLOT Columns where the solid layer consists of the particles of a solid support which were deposited on the inside tube wall.
3.3 Detectors, are devices that indicate the presence of eluted components in the carrier gas emerging from the column.
3.3.1 Differential Concentration Detectors, measure the instantaneous proportion of eluted sample components in the carrier gas passing through the detector.
3.3.2 Differential Mass Detectors, measure the instantaneous rate of arrival of sample components at the detector.
3.3.3 Integral Detectors, measure the accumulated quantity of sample component(s) reaching the detector.
3.3.4 Spectrometric Detectors, measure and record spectra of eluting components, such as the mass spectrum of the infrared spectrum.
3.4 Traps, are devices for recovering sample components from the mobile phase eluting from GC columns.
4. Reagents
4.1 Carrier Gas is the Mobile Phase used to sweep or elute the sample components through and from the column.
4.2 The Stationary Phase is composed of the active immobile materials within the column that selectively delay the passage of sample components by dissolving or adsorbing them, or both. Inert materials that merely provide physical support for the stationary phase or occupy space within the column are not part of the stationary phase.
4.2.1 Liquid Stationary Phase is one type of stationary phase which is dispersed on the solid support or the inner column wall and causes the separation of the sample components by differences in the partitioning of the sample components between the mobile and liquid phases.
4.2.2 An Active Solid is one that has ab- or adsorptive properties by means of which chromatographic separations may be achieved.
4.3 The Solid Support is the inert material that holds the stationary (liquid) phase in intimate contact with the carrier gas flowing through it. It may consist of porous or impenetrable particles or granules which hold the liquid phase and between which the carrier gas flows, or the interior wall of the column itself, or a combination of these.
4.4 The Column Packing consists of all the material used to fill packed columns, including the solid support and the liquid phase or the active solid.
4.4.1 The Liquid-Phase Loading describes the relative amount of liquid phase present in a packed column when the column packing consists only of the liquid phase plus the solid support. It is usually expressed as weight percent of liquid phase present in the column packing:
4.5 Solutes are the introduced sample components that are delayed by the column as they are eluted through it by the carrier gas.
4.6 Unretained Substances are not delayed by the column packing.