Page 36 - Tandem Techniques

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accommodate the elution characteristics of the gas chromatograph and, on the other, to meet the inlet
requirements of the tandem instrument.

Liquid Chromatography

A block diagram of the basic liquid chromatograph is shown in Figure 1.4. The liquid chromatograph
consists of a solvent supply system that provides at least dual solvent capability and, in some
instruments, four solvents may be selectively available. The different solvents are blended by means of
a solvent programmer that can change the solvent composition according to a selectable range of time
functions, and also provide isocratic development for chosen periods. The blended solvent then passes
to the injection valve that places the sample onto the column. When used with tandem systems, the
sample volume can range from 0.1 to 20 µl and is chosen to be appropriate for the particular column
employed and the type of instrument with which the chromatograph is to be associated. There are also a
number of different types of column employed in LC, but virtually all those used with tandem
instruments utilize the standard sample valve for injection purposes. The valve and the attached column
should be situated in a thermostatted oven.

Figure 1.4
The Basic Liquid Chromatograph