Partial derivative derivation of isothermal multicomponent mixtures needed for the development of universal models of multiphase multicomponent flows is presented. The equations of state and the derivative approximations as functions of temperature and pressure for the elementary mixture constituents are assumed to be known. Two kinds of multicomponent mixtures are investigated: gas mixtures and mixtures of liquid and microscopic solid particles of different chemical substances homogeneously mixed within the liquid. In addition, one component liquid-gas and a solid-liquid equilibrium mixture is considered.