Calcium-bound organo-mineral complexes in soil belong to a kind of outer sphere complexes.SO₄^2- in sodium sulphate,as a coordination agent,can destroy Ca-bound organomineral complexes by coordinating Ca²⁺ and extract Ca-bound humus.This work examined the ability of sodium sulphate to destroy Ca-bound organo-mineral complexes and to extract humus from soils and synthetic organo-mineralcomplexes.It was proved that sodium sulphate was a suitable agent to differentiate Ca-bound complexes from Fe/Al-bound complexes in soils.A detailed method for separating Ca-bound complexes by sodium sulphate is described.Finally,a follow-up extractant to sequentially extract Fe/ Al-bound complexes from soils is also proposed.