Page 38 - Tandem Techniques

Page 20

inherent limitations of the detector, the high resolution theoretically possible from such columns cannot
be realized.

The packed LC column, on the other hand, is well developed and is the 'work horse' of the separation
chemist. Generally, the diameter of the analytical column can range from 0.5 mm to 10 mm and its
length from 2 cm to 2000 cm although columns up to 10 m long have been fabricated [2]. The packing
is usually silica or silanized silica (reverse phase) but polystyrene cross-linked with divinyl benzene has
become more popular particularly for ion exchange media. This is because bonded silica ion-exchange
media are unstable at high salt concentrations or outside the pH range of about 5-8. LC packings are
normally available having particle diameters of 3, 5, 10 and 20 µm. Low-resolution, high-speed
columns should be short, with relatively wide diameters and are packed with very small particles. An
example of a high-speed separation [13] is shown in Figure 1.5.

Packing, Hypersil, (silica) particle size 3 µm., Column Length 2.5 cm,
Column Diameter 2.6 mm, Mobile phase 2.2% methyl acetate in n -pentane,
Mobile Phase Velocity 3.3 cm/sec
Figure 1.5
The Separation of a Five -Component Mixture in 3.5 Seconds