Carrier mobile phase

The mixture to be separated and analyzed may be either a gas, liquid, or a solid in some instances. All that is required is that the materials be stable, have a vapor pressure of 0.1 torr at the operating temperature and interact with the column material (either a solid adsorbent or a liquid stationary phase) and the mobile phase (carrier gas). The result of this interaction is the differing distribution of the sample components between the two phases, resulting in the separation of the sample components into zones or bands. The principle that governs the chromatographic separation is the foundation of most physical methods of separation, for example, distillation and liquid-liquid extraction. 

Column. A metal, plastic or glass tube packed or internally coated with the column material through which the sample components and mobile phase (carrier gas) flow and in which the chro-... 

Flow controller. A device to regulate the flow of mobile phase (carrier gas) through column. 

Flow programming. A procedure in which the rate of flow of the mobile phase (carrier gas) is systematically increased during a part or the whole of the separation of higher boiling components. 

Flowrate. Fc- The volumetric flow rate of the mobile phase (carrier gas), in cm3/min, measured at the column temperature and outlet pressure. 

Interstitial volume. Vj (Vg). The volume occupied by the mobile phase (carrier gas) in a packed column. This volume does not include the volumes external to the packed section, i.e., volume of sample injector and volume of the detector. In GC it corresponds to the volume which would be occupied by the carrier gas at atmospheric pressure and zero flowrate in the packed section of the column. 

Liquids are virtually incompressible, and gases are readily compressed. This has a major impact on GC because the mobile phase carrier gas is compressed at the head of the column, resulting in a variable flow rate through it. We need to take a closer look at this phenomenon and see what the consequences are for GC operating parameters. 

Modem GC uses capillary columns (internal diameter 0.1-0.5 mm) up to 60 m in length. The stationary phase is generally a cross-linked silicone polymer, coated as a thin film on the inner wall of the fused silica (Si02) capillary at normal operating temperatures, this behaves in a similar manner to a liquid film, but is far more robust. Common stationary phases for GC are shown in Fig. 32.4. The mobile phase ( carrier gas ) is usually nitrogen or helium. Selective separation is achieved as a result of the differential partitioning of individual compounds between the carrier gas and silicone polymer phases. The separation of most organic molecules is influenced by... 

Phase ratio, is defined as the volume occupied by the mobile phase (carrier gas) relative to the volume occupied by the stationary phase per unit length. In WCOT columns /3 is the ratio of the internal radius, r (mm), to the... 

Of the many separation modes of HPLC, GPC is the simplest. This is now most commonly called SEC. In this mode, the separation of substances proceeds according to the hydrodynamic radius, or effective size , of each solute molecule in solution, and is relatively independent of the chemical or electronic nature of the substances and their mobile phase carrier. This independence includes the idea that the column packing, usually composed of porous particles of controlled pore size, is also relatively inert toward the solutes and solvents employed so that adsorption/desorption phenomena do not enter into account. 

Another important instrument required in modem LC is a sensitive or selective detector for continuous monitoring of the column effluent. In GC. the differences in physical properties of the mobile phase (carrier gas) and the sample are great enough for universal detectors with good sensitivity to be used (e.g., flame ionization detector, thermal conductivity detector, - Gas Chromatography). The problem in LC is that the physical properties of the mobile phase and the sample are often very similar, which makes the use of a universal detector impossible. Nevertheless, presently available LC detectors are very sensitive, are generally selective, and have a relatively wide range of applications (see Table 1). 

Martin and Synge (22) derived an expression for the total quantity q of solute in plate n and the volume of mobile phase (carrier gas) that passes through the column ... 

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