A method for assessing polymeric additive content A in a polymeric particle mixture may comprise determining a concentration B of a metal cation in a polymeric particle mixture comprising parent polymeric particles and polymeric additive particles, wherein the metal cation is selected from alkali earth metals and alkali metals, other than sodium (Na), and the metal cation is capable of forming a water-soluble base; determining a concentration C of the metal cation in the parent polymeric particles; determining a concentration D of the metal cation in the polymeric additive particles; and calculating a polymeric additive content A using formula A = (B - C) / D.