Page 497 - Tandem Techniques

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Chapter 13
Tandem Systems Involving Capillary Electrophoresis As The Separation Technique

Capillary electrophoresis can provide extremely high plate efficiencies, and although the selectivity of
the electrophoretic process is not as great as that attainable from liquid chromatography, the resolution
provided by the system is still extremely high. It follows that the combination of an electrophoretic
instrument with a spectrometer would be an extremely useful tandem system.

The first on-line capillary electrophoresis/mass spectrometer tandem instrument was reported by
Olivares et al. [1] and Lee et al. [2] who coupled the capillary column of the electrophoretic system to a
quadrupole mass spectrometer, using an atmospheric pressure ionization electrospray interface. A
diagram that depicts the basic arrangement is shown in Figure 13.1. As a result of the small flow rates
that are involved (usually about 1 µl/min) the design of the interface is critical. The electrophoresis is
carried out employing a high-voltage power supply giving 0 to 60 kV. The high-voltage electrode, one
end of the capillary tube, is contained in an insulated box fitted with remote manipulators. The fused
silica capillaries are 10 cm long, 100 µm I.D.. The cathode end of the capillary (the low-voltage end), is
terminated by a stainless steel sheath 300 mm I.D. and 400 mm O.D., the potential of which is
controlled by a separate 0-5 kV power supply. The stainless steel end functions as both the
electrophoresis cathode and the electrospray needle, electrical contact being maintained with the
solution by means of the stainless steel collar.