Hidrológiai Közlöny 1967 (47. évfolyam)

7. szám - A „Szervesanyag meghatározási problémák édesvizekben” című 1966. szeptember 25–28. között Tihanyben rendezett Szimpózium előadásai - Shapiro, Joseph: Különböző tavakból száramzó szervesnyagok összehasonlítása

HIDROLOGIAI KÖZLÖNY 47. ÉVFOLYAM 7. SZÁM 289—33C. oldal Budapest, 1967. július PROBIEMS OF ORGANIC MATTER DETERMINATION IN FRESH WATERS Symposium Budapest—Tihany, Hungary 25—28. Sept. 1966. Yellow Organic Acids of Laké Water: Differences in their Composition and Behavior* JOSEPH SHAPIR 0*» Abstract It is shown that Sephadex elution patterns of the yellow organic acids of laké water are characteristic of the extracts under a variety of isolation and experimentál conditions and may therefore be compared with each other. In this manner four distinct elution pattern Types have been found among 22 Minnesota lakes. The patterns correlate perfectly with the irón holding capacity of the extracts and show that it is the high molecular weight components which are mostly responsible for peptizing iron. No longer can the color of a laké water have any meaningin itself. In previous papers [1, 2, 3] I have presented methods for extraction and purification of the yellow organic acids of natural waters, and have discussed their probable relation to the inorganic constituents of laké water, particulartly the trace metals. One of the features most investigated is the capacity of the acids, or their salts, to hold large amounts of iron in apparent solution — probably as a peptized sol — at high pH and high redox values. In a more recent paper [4] a comparison was presented of the capacity of extracts from different lakes to perform this function. The results, shown in Fig. 1, demonstrate that although the extracts behave in a similar fashion qualitatively they act very differently quantitatively. For example, at pH 7, 1 mg of acid may hold between 6 and 15 micromoles of iron depending upon the origin of the acid. Similarly, a given quantity of color is capable of holding more or less iron, again depending upon the source of the extract. The most reasonable explanation for these differences in behavior is, of course, that not all extractable substances may be capable of peptizing iron, and that the proportion of these nonreactive substances may vary from laké to lake. * 1. Contribution no. 38 from the Limnological Research Center. 2. This work was supported by U. S. P. H. S. Research Grant WP-771. 3. Acknowledgement is made to Mrs. Margaret Weeks for her careful assistanee. ** Limnological Research Center, University of Minnesota. Minneapolis, Minn. USA. Alsó it is likely that even those substances which do participate in the iron holding capacity may do so to different degrees. In an attempt to clarify the situation it was decided to fractionate the extracts from various lakes and compare the results with the iron holding capacities of these extracts. Iron holding capacity of yellow acids, extracted from different lake waters, as a function of pH. side shows the capacity per milligram of acids, the right side per unit quantity of color Procedure The extracts were prepared from various lake water samples in the manner previously described [3] using ion exchange, freeze concentration, acidification, and extraction with butanol, followed by evaporation of the butanol to a dry residue. Fractionation was done by the gelfiltration procedure with "Sephadex" gel (Pharmacia, Uppsala, Sweden), used by various investigators for soil humic substances [5], by Povoledo and Gerletti for lacustrine sediment extracts [6], and recently by Gjessing for humic substances of natural waters [7].