The Basic Column Chromatograph
A chromatograph consists of five basic units and these units, although possibly designed differently for different systems, are essential for all types of chromatograph, including both gas and liquid chromatographs. The layout of all the five essential units is shown in figure 24. They consists of a mobile phase supply, a sampling system, a column and column oven including a temperature controller and temperature programming system. The temperature controller and programmer will probably have its own microprocessor which may also be under the control of the data acquisition and processing computer. The column eluent will pass to an appropriate detector and its associated electronics. There may be more than one detector and they may be employed in parallel or in series and individually controlled and monitored. The final unit will be a computer and data acquisition system and may include a simple potentiometric recorder to monitor the chromatogram in real time, if this is not provided by the computer.
Figure 24 The Basic Chromatograph
The Mobile Phase Supply
The first unit, the mobile phase supply, can range in complexity from a simple gas cylinder connected to a flow controlling valve for a gas chromatograph, to a complex multi-piston pump supplied by four or five solvent reservoirs and fitted with both flow programming and gradient elution facilities, each with its own controlling micro-processor. For a gas chromatograph the gas supplies will vary depending on the type of detector employed and column that is used. If gases are being analyzed then a katharometer detector will probably be appropriate and thus helium will be used as the carrier gas to provide the best sensitivity. If a flame ionization detector (FID) is to