INDIRECT ASSAY OF SULFATE IN PRESENCE OF PHOSPHATE USING ATOMIC ABSORPTION SPECTROMETRY

The final equilibrium in the formation of solid BaSO4 is reached very slowly when solutions with Ba2+ and SO 42− are mixed. The ion product Lp″ = [Ba2+] · [SO 42−] of the concentrations remaining in solution however becomes rather constant after about 1/2 hour already, especially when the suspension is seeded with a specially prepared BaSO4. The apparent solubility product–somewhat larger than the theoretically expected value–varies with the composition of the solution (other solutes present than Ba2+ and SO 42−) and the equilibration time, but it is independent of the Ba/SO4‐ratio. This allows a great improvement of the indirect determination of sulphate by adding barium and determining its excess by atomic absorption. Copyright © 1969 Verlag GmbH & Co. KGaA, Weinheim