Speciation of manganese in fresh water-I Use of EPR studies.

The process of standardization of the use of electron paramagnetic resonance (EPR) spectrometry in the determination of Mn(II) species in aqueous solution by comparison with atomic absorption spectrometry (AAS) is discussed. It is shown that EPR signals obtained from standardized aqueous solutions of manganese(II) perchlorate and nitrate in the concentration range of 0.05-2 mg/l. do not vary significantly over the pH range 2.1-7.0. Study of the effect (on the manganese EPR signals) of the addition of inorganic ions commonly found in significant concentrations in natural waters, viz. chloride, sulphate and bicarbonate, has shown that such ions, at the levels reported to occur in surface fresh waters, will not complex manganese(II); however, evidence is obtained that humic acid/manganese complexes could be present in such waters. The EPR signals are not affected by ionic strengths of the levels found in fresh waters.