Topics - chromatograph
is an instrument that is used to carry out chromatographic separations. The chromatograph consists of five different entities. The mobile phase supply system, the injection or sampling system, the column and column oven, the detector and the data acquisition and data processing system. In gas chromatography the mobile phase supply system consists of gas tanks, reducing valves, flow controllers and pressure gauges. In liquid chromatography the mobile phase supply system consists of a set of solvent reservoirs, sparged with helium gas to remove dissolved air, a solvent selector valve, a solvent programmer and a high pressure pump. In gas chromatography, the sampling system, in its simplest form, consists of a septum injector and a sampling syringe. In its more sophisticated form, it will include an automatic sampling device that may also be under the chromatograph computer control. Liquid chromatography sampling systems consist of a high pressure sample valve that may also have the sample supplied to the valve from an automatic sampling device. Both gas and liquid chromatography have ovens that are usually temperature programmable, the temperature of the gas chromatographic oven range from 5oC to 350oC and the liquid chromatography oven from about 5oC to 120oC. Gas chromatography usually employs capillary columns whereas packed columns are the most common type of liquid chromatography column. The most common gas chromatography detectors are the flame ionization detector (FID) the Nitrogen Phosphorous Detector (NPD) and the thermal conductivity detector or the hot wire detector (HWD). The three most common liquid chromatography detectors are the UV detector, the fluorescence detector and the refractive index detector (the RI detector). The data acquisition and processing system is very similar for both types of chromatography. They consist of a scaling amplifier and an A/D converter, the output of which is fed to a suitable computer and associated printer. Retention times, retention ratios, peak heights and peak widths are calculated and retention data and quantitative analyses are calculated and then printed out.