Chemical potential is not only the criterion to estimate chemical equilibrium but also the cause of diffusions, phase transitions and chemical reactions. In this paper, based on the energy postulate and thermodynamic principles, a generalized expression of chemical potential with the effect of external fields was derived, which shows that chemical potential not only depends on temperature, pressure, and molar fraction of the components, but also is strongly affected by the characteristic parameters of external fields. The gravitational, centrifugal, electric and magnetic chemical potentials were deduced from this generalized expression; especially the chemical potential of dielectric in electric field was also obtained. As an application of this new chemical potential expression, the effects of charged particles as condensation nuclei on droplet growth were investigated. The theoretical results show that the amount of charge can strongly affect the growth of droplets, the critical radius of droplets becomes smaller, and a stable droplet or a droplet which could continue to grow up through condensation can form depending on the amount of charge. This work provides a new method for the study of mass transfer enhanced by external fields. (c) 2012 Elsevier B.V. All rights reserved.