A new enrichment approach is described to improve the sensitivity of the asymmetrical flow field-flow fractionation, with and without ICPMS online coupling for elemental detection. For the slot outlet technique, a part of the laminar carrier stream is removed through an additional pump. This allowed an enrichment of the colloidal particles in the separation channel up to a factor of 14. Additional improvements of the separation efficiency permitted us to separate colloids with differences in their molecular masses of only 2 kDa. Different polymer standards, proteins, and synthesized tracer colloids, as well as real samples (wastewater, liquid manure, serums) were used to assess the performance of the new technique.

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A bstrttc t. By comparison of the UV-VIS absorption spectra of solutions of sulfur and of synthesized sulfur nitrogen compounds in ammonia and by comparisoii of their light induced changes \re conclude thatS,NH, S,NH and S,NH are besides polysulfides H,S, the main compoundsin sulfur ammonia solntions. The equilibria between the species are shifted reversibly by photoinduced reartions and permanently by Ag,S precipitation (with AgNO,). As the only and final product on Ag2S precipitation S,N,H is identiiied which by oxidation forms S,N,. Identifizicrung der wesentlichen Schwefel-Stickstoffverbindungen in Schwefel-Ammo-niakl6sungen I n he1 t s i i bersicht. Durch Vergleich der UV/VIS-Absorptionsspektren der Losungen V O I~ Scliwcfel sowie von synthetisierteii Schwefel-Stickstoffverbindungen in flussigem Ammoniak und durch Vergleich der Anderungen der Spektren bei Lichteinwirkung folgern wir, daB S,NH, S,NH und S,NH nebcn Polysulfiden als Hauptbestandteile in Schwefel-Ammoniaklosungen vorliegen. Die Gleichgewichte zwischen den Verbindungen werden durch photochemische Reaktionen revrrsibel, dnrch Ag,S-Bnsfallung irreversibel verschoben. Als Endprodukt bei der Ag,S-.~usfallnng verbleibt S,N,H in der Losung, das diircli Oxydation in S,N, iibergcht.