Dissolved organic carbon (DOC) such as humic and fulvic acids have a high ability to form stable complexes with many metal ions. Also otherwise insoluble elements may be mobilized by complexolysis. Detection of the humic substances can be made with size exclusion chromatography (SEC) with UV/Vis and fluorescence detection. To detect the metals that different organic compounds carry the metal content in the eluent can be analyzed. However, the phosphate buffer that is used in the reference method is not well suited since phosphate and hydrogen phosphate ions are excellent complexing agents for many metals. In this work ammonium nitrate buffer was evaluated and used.
To decrease the analytical cost and streamline the analytical procedure an LC-system (Agilent 1260) was connected to an MP AES (Agilent 4200). After separation and spectroscopic measurements the eluent was lead to the nebulizer and the metal content in the eluent was determined as a function of time.
When acidic shale residues come in contact with wood chips, acidic hydrolysis and microbial degradation generate a complex mixture of hydrophilic organic compounds and acid rock drainage (ARD). If no subsequent condensation occurs the released organics would mainly contain low molecular weight carbon compounds (LMWOC). The fluorescence at 443 nm after exitation at 345 nm reveals that compounds of humic and fulvic character are present in the leachates. The content of manganese in the more complex forms of organic compounds is limited and it is mainly associated with LMWOC. Hence, humic compounds are not a good carrier of manganese in this type of system.
By using ammonium nitrate as buffer solution the separation was almost identical to the phosphate buffer. The results show that LC and MP AES can be used for analysis of the metal content as a function of size of organic carriers, such as humic substances and LMWOC. By using MP AES for metal analysis, operating cost is significantly decreased compared to hitherto used methods based on ICP. The results also indicate that substances with humic character form during acidic and microbial degradation of wood. From an environmental perspective this is of importance since several organic compounds facilitate metal mobilization.