Page 498 - Tandem Techniques
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Page 484
Figure 13.1
The First Capillary Electrophoresis Quadrupole
Mass Spectrometer Tandem Instrument
The electrospray ionization is carried out in a stainless steel tube, 2.54 cm long and 2.3 cm I.D. The end
of the cylinder contains a hole 0.475 cm in diameter, that acts as a focusing ring and is biased at 190 V
dc. The copper ion-sampling nozzle is held at ground potential, and has a 0.5 mm sampling orifice. The
whole spray system is heated to 60°C by a number of appropriately placed cartridge heaters. A curtain
of nitrogen (at a flow rate of 2.5 1/min) is maintained between the focusing ring and the nozzle that
provides a counter flow as an aid in solvent evaporation. The vacuum system has three differentially
pumped stages, which maintains the necessary pressures in the different parts of the mass spectrometer,
and ensures that a pressure of 2 x 10-6 torr is held in the mass analyzer by means of a 500 1/sec
turbomolecular pump.
In most cases the solvent used for the electrospray was composed of 50/50 methanol water containing
10 M KCI. The initial test mixture contained
-4
