Electrophoresis band spreading

The first approach to interfacing CE with MS was reported by Smith et al.48 when they incorporated the electrospray ionization (ESI) technique introduced by Dole et al.66 This development was based on the recognition that it is not necessary for the detection end of the CE capillary to be immersed in the buffer reservoir as conventionally practiced, as long as it is biased negative of the cathode potential (assuming a cathodic detector end). The ESI was created directly at the terminus of the CE capillary, avoiding any postcolumn region that would contribute to extracolumn band spread or analyte adsorption. A quadrupole mass filter was combined with ESI to produce the first on-line MS detection with capillary electrophoresis. 

Field-inversion electrophoresis is predicted to give a much better spreading of the bands. The idea here is to use a secondary, weaker negative field to speed up the relaxation of the reptation tube between the primary (forward) electrophoretic pulses. This is therefore similar to intermittent field electrophoresis, where a secondary field instead of Brownian motion is used to decrease the tube orientation. By choosing the field and time ratios and properly, one can optimize the band... 

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