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transmits a signal to a recorder, integrator or computer. Typical run times are between

10 and 30 min. A typical capillary electrophoretograph is shown in Fig. 10.18.

This free solution method is the simplest and most widely practised mode of

capillary electrophoresis. However, while the generation of ionised groups on the

capillary wall is advantageous via the introduction of electroendosmotic flow, it can

also sometimes be a disadvantage. For example, protein adsorption to the capillary

wall can occur with cationic groups on protein surfaces binding to the ionised

silanols. This can lead to smearing of the protein as it passes through the capillary

(recognised as peak broadening) or, worse, complete loss of protein due to total

adsorption on the walls. Some workers therefore use coated tubes where a neutral

coating group has been used to block the silanol groups. This of course eliminates

electroendosmotic flow. Therefore, during electrophoresis in coated capillaries, neutral

species are immobile while acid species migrate to the anode and basic species to the

Peptide

1 Lys-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg

2 Met-Lys-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg

3 Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg

4 Ser-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg

5 Ile-Ser-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg

Source:Courtesy of Patrick Camilleri and George Okafo, GSK Ltd.

Time (min)

UV absorbance

15 16.5 18 19.5 21 22.5 24 25.5

1

2

3

4

?

5

Fig. 10.18Capillary electrophoresis of five structurally related peptides. Column length was 100 cm

and the separation voltage 50 kV. Peptides were detected by their ultraviolet absorbance at 200 nm.

430 Electrophoretic techniques