Modification of a simple method for determination of gamma-2 phase of dental amalgam

Evidence is presented for the formation of a tin-citrate ligand complex that severely limits the shelf life of the SnCl2-citric acid solutions used to standardize the reaction of the gamma 2 phase of dental amalgam with PMA. Early ligand complex formation probably accounts for the lack of linearity in the SN+2-PMA reaction seen at low SN+2 concentrations and is a potential source of error in the original, analytical method outlined by Kropp. Substitution of 1% HCl (0.27N) for 5% citric acid throughout the procedure is proposed. It was noted, however, that Sn+2in 1% HCl undergoes oxidation to Sn++ and thus limits shelf life of these solutions.