Abstract: During the injection of neutral solute in CEC, the partition equilibrium of solute between mobile phase and stationary phase will lead to an inhomogeneous distribution along column axes and bring on a self enrichment effect. Based on the relaxation theory, the transfer process of solute in column is delt with by no dimension method. The transfer equation forms an increasing series by degree. This equation is also solved with production function, and the second central moment of the profile is derived. Compared to the common injecting process and self enrichment, the expression which describes the effect of injecting time and retention value on enrichment is theoretically held and experimentally investigated with two drugs: mephenytoin and benzoin. The results show that the longer the injecting time and the larger the capacity factor of solute, the stronger the self enrichment effect. Under the conditions of constant column efficiency, the self enrichment effect can increase more than 10 fold detection sensitivity to the experimental solute.

Key words: CEC, Self enrichment, Injecting time, Relaxation theory