Coion
= Coion
A <coion> has <electric charge> of the same sign as the reference interface or particle. Its <number density> is depleted near that interface in the simplest <Poisson-Boltzmann equation> description. A <counterion> has the opposite sign. These roles depend on the reference charge: near a positively charged sphere in magnesium chloride, magnesium ions are coions and chloride ions are counterions.