『Abstract
　Analytical methods used for determining dissolved Fe(II) often yield inaccurate results in the presence of high Fe(III) concentrations. Accurate analysis of Fe(II) in solution when it is less than 1％ of the total dissolved Fe concentration (FeT) is sometimes required in both geochemical and environmental studies. For example, such analysis is imperative for obtaining the ratio Fe(II)/Fe(III) in rocks, soils and sediments, for determining the kinetic constants of Fe(II) oxidation in chemical or biochemical systems operating at low pH, and is also important in environmental engineering projects, e.g. for proper control of the regeneration step (oxidation of Fe(II) into Fe(III)) applied in ferric-based gas desulphurization processes. In this work a method capable of yielding accurate Fe(II) concentrations at Fe(II) to FeT ratios as low as 0.05％ is presented. The method is based on a pretreatment procedure designed to separate Fe(II) species from Fe(III) species in solution without changing the original Fe(II) concentration. Once separated, a modified phenanthroline method is used to determine the Fe(II) concentration, in the virtual absence of Fe(III) species. The pretreatment procedure consists of pH elevation to pH 4.2-4.65 using NaHCO3 under N2(g) environment, followed by filtration of the solid ferric oxides formed, and subsequent acidification of the Fe(II)-containing filtrate. Accuracy of Fe(II) analyses obtained for samples (Fe(II)/FeT ratios between 2％ and 0.05％) to which the described pretreatment was applied was＞95％. Elevating pH to above 4.65 during pretreatment was shown to result in a higher error in Fe(II) determination, likely resulting from adsorption of Fe(II) species and their removal from solution with the ferric oxide precipitate.』

1. Introduction
2. Proposed pretreatment procedure
3. Materials and methods
　3.1. Analyses
　3.2. Reagents
　3.3. Pretreatment procedure
　3.4. Experimental
　　3.4.1. Preliminary experiment
　　3.4.2. Suggested procedure verification experiments
4. Results
　4.1. Determining the minimal pH required for efficient Fe(III) precipitation in the pretreatment procedure
　4.2. Determining the Fe(II) impurity concentration in the Fe2(SO4)3 background solution
　4.3. Applying the suggested method (pretreatment + analysis by the modified phenanthroline method) to samples with different Fe(II):FeT ratios at various pH values during pretreatment
5. Discussion
6. Conclusions
Acknowledgements
References