  We present a theory that enables us to calculate the effective surface charge
of colloidal particles and to efficiently obtain titration curves for different
salt concentrations. The theory accounts for the shift of pH of solution due to
the presence of 1:1 electrolyte. It also accounts self-consistently for the
electrostatic potential produced by the deprotonated surface groups. To examine
the accuracy of the theory we have performed extensive reactive Monte Carlo
simulations, which show excellent agreement between theory and simulations
without any adjustable parameters.
