A method of differential AOX-analysis, i.e. the simultaneous determination of AOCl, AOBr and AOI is described. Individual steps of the method including enrichment at activated carbon, combustion in an oxygen stream and ion-chromatographic detection were optimized. In most cases quantitative recoveries of various organic Cl, Br and I containing substances of different polarity and structure were obtained. The method was applied to the determination of AOX-fractions in municipal and hospital wastewater. A good agreement between conventional coulometric and the described ion-chromatographic determination was found. High concentrations up to 130 microg/L I of organic iodine compounds were measured in the influent and effluent of a municipal treatment plant in Berlin and up to 10 mg/L I in a hospital waste-water.
Crystals of the adducts Zn(SCN)2 · (C6H12N4)2 (1), and {Zn(SCN)2 · C6H12N4 · 2H2O}n (2) were obtained by crystallization from aqueous solutions containing hexamethylenetetramine, potassium thiocyanate and zinc nitrate or zinc sulfate, resp., under identical conditions, as two totally different products. 1 crystallizes orthorhombically, space group P nmm, Z = 2, a = 622.4(5), b = 1152.3(7), c = 1394.0(9) pm; 2 is monoclinic, space group C2/c, a = 984.4(3), b = 1217.0(5), c = 1257.4(6) pm, and β = 111.69(5)°. The crystal structure of 1 contains discrete molecules of the complex, in which the zinc ion is tetrahedrally coordinated by two NCS ligands, and two hexamethylenetetramine molecules, which act as monodentate ligands. In 2 however, the zinc ions are octahedrally coordinated. A “supramolecular” structure is formed: The hexamethylenetetramine molecules act as bridging bidentate ligands and connect [Zn(H2O)2(NCS)2] units forming zig-zag chains. Adjacent chains are interconnected via hydrogen bonds. The formation of the two compounds with different coordination may be due to the fact, that the educts Zn(NO3)2 · 4H2O and ZnSO4 · 7H2O contain Zn(H2O)4 and Zn(H2O)6 moieties, resp., and that these species are retained in solution.
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