An interface which permits both gradient elution capillary electrochromatog
raphy (CEC) and the coupling of high performance liquid chromatography (HPL
C) to CEC is described. Mobile phase from an HPLC system with continuously
variable composition is supplied on demand to the inlet of a CEC column, wi
thout the possibility of pressure driven flow. The interface also allows fr
actions separated by either reverse phase or normal phase HPLC to be transf
erred to a CEC column operated in reverse phase mode for further separation
.