Page 398 - Tandem Techniques

Page 382

An electrospray interface has been designed specifically for use with liquid chromatography micro
columns. Micro columns employ very low flow rates and the peaks are eluted in very small volumes so,
although the mass placed on column is very small, the concentration of the solute in the eluent is still
relatively high. Their design and use for the analysis of biological samples has been reviewed by Yates
et al. [35] and a diagram depicting the general properties of the micro column electrospray interface is
shown in Figure 9.39.

Figure 9.39
Electrospray Interface for Liquid
chromatography Micro-columns (ref. 35)

The column flow passes through a fused quartz capillary, which may be a conduit from the column, or
the column itself, and is joined by the sheath liquid flow at a T junction. The two streams pass down a
jacket tube through which flows a warm current of sheath gas, the different streams meeting at the jet
tip. The quartz capillary projects a little beyond the sheath gas nozzle and the mist of drops are formed
at the liquid cone beyond the jet inducted by a potential of 2-4.5 kV. This potential is set up between the
end of the jet and the end of the heated capillary situated ahead of the electrospray jet. The solvent
evaporates and the ions that are formed pass into the heated capillary where the last traces of solvent are
removed. At the end of the capillary the ions are focused by a tube lens