Basic characterization of reference NOM from Central Europe - Similaritiesand differences

The FA and HA fractions represent 20 to 50% of the DOC of the original samp les, depending on the origin, and serve as reference materials. The origina l aqueous samples and the aqueous solutions of the reference materials were characterized with methods suited for measuring samples at natural concent rations. The DOC normalized values of the spectral absorbances (lambda = 25 4 nm; lambda = 436 nm) in the original water samples were highest for the b rown water and brown coal water and lowest for the secondary effluents. The FA fi actions were similar in the UV-absorbance with the exception of the low-absorbing groundwater FA, reflecting a low density of double bonds. The DOG-normalized proton capacity of the FA fractions (10 to 20 mu mol/mg) wa s highest for the brown coal, brown water, and soil-derived samples and aga in lowest for the groundwater FA. The high values are due to a higher contr ibution of the weak acids of phenolic type. Specific data for copper comple xation capacity (0.5 to 2.5 mu mol/mg) went parallel to the proton capacity . The characterization of the FAs by gel chromatography with organic carbon detection revealed three major fractions. The refractory part at short ret ention time dominated in the brown water and soil-derived samples, whereas the fractions for the lower molecular mass acids at long retention times we re dominant in the secondary effluent and the brown coal isolate. Compariso n with UV-detected chromatograms revealed a strong decrease in the specific absorbance of the secondary effluent. Up to 3% of the total mass of the FA s could be identified as hydrolyzable amino acids with the highest yield in the sample from secondary effluent and the lowest one in the groundwater s ample. The nitrogen content was always higher in the FAs compared to the HA s of the same origin. The application of gel chromatography fluorescence an d fluorescence decay time distribution analysis turned out to be a useful t ool to differentiate between the different fractions of NOM, the isolates o btained by different methods (e.g., XAD-8, membrane separation) and the fra ctions of the samples from different origin and age. This is of special val ue, for the information can also be obtained for samples with natural NOM c oncentrations, even though further investigations required for full underst anding of the data. This work is part of a multi-disciplinary research prog ram (ROSIG: Refraktare Organische Sauren in Gewassern), funded by the Germa n Research Association (DFG). (C) 1999 Elsevier Science Ltd.