According to thermodynamics, the integral optimizing functional of separation efficiency (DS), which is the mixed S entropy change between initial and final states directly associated with separation efficiency, was presented to indicate integral separation efficiency for any zone separation method by further considering the entropy change from the uniform to the arbitrary distribution of solute zones. Physically, as a system property, DS is equal to the amount of information that the S solute system obtains from its separation surrounding, or separation system. It can be quantitatively related to the irreversibility of separation processes in the entropy balance equation, and corresponds to the extent of Boltzmann order. In separation science, DS corresponds to the quantity of separated solutes. For any arbitrary distribution of solute zones, DS S S can be calculated directly from the distributions and relative positions of solute zones and the number of moles of solutes. Thus DS can be calculated directly from the separation results of chromatography and electrophoresis to indicate separation S efficiency integrally and quantitatively. For example, for Gaussian distributions of zones, DS can be calculated directly from S the standard deviations of the peaks (s), the distance between the centers of gravity of adjoining zones (Dx) and the number of moles of the solutes (n) or the peak height (h). A quasi-inverse relation between DS and separation pureness of solutes S (w) was found numerically. In any effective separation process, DS is always a negative value, and the more negative DS S S is, the better the separation efficiency is. The computer simulation supported the above characters of DS . The discovery of S DS is a part of the nonequilibrium thermodynamic separation theory, which can be used to integrally optimize and S time-varying control the complete separation systems-the aggregates of solute systems and separation systems.