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stainless steel sheath tube (254 µm I.D. and 508 µm O.D.), through which the make-up buffer or
solvent flow was introduced. A larger stainless steel tube (584 µm I.D. and 902 µm O.D.), placed
concentrically round the inner capillaries, served as the nebulizing gas conduit, through which nitrogen
was passed at a pressure of 50 psi.

Figure 13. 5
The Ion Spray CE/MS Interface

The sheath flow liquid was 2 or 5 mM ammonium formate in methanol, and delivered at a flow rate of
10 µl/min. The ion trap mass spectrometer was the bench-top Varian Saturn II equipped with an
atmospheric ionization source. An example of a total ion current capillary electropherogram is shown in
Figure 13.6. It is seen that the mass of sample represented by each peak was, on average, about 45 fmol
(i.e. 45 x 10-15 mol). Now assuming an average molecular weight for the different alkaloids to be
similar to that of berberine (i.e. 326), the actual mass of the solute present will be,

For analysts familiar with the mass spectrometer, the mass of 14.7 pg will permit a rational comparison
with other instruments, whereas for those employing UV detection, the value of 0.015 ng will have
more meaning.