Capillary electrophoresis is a useful tool for the analysis of nucleotides. Their charge depends on the pH of the buffer system used. An equation is developed for calculation the partial charge of acids with more than one dissociation constant in dependence on the pH and the ionic strength of the buffer. There is no limitation to the number of dissociation constants. The partial charges and from these the relative mobility according to Offord were calculated for 4 nucleotid-monophosphates. They agree very well with the experimental electrophoretic data.