Mrs/Miss Novotnik,

Generally, there has scarce literature in the topic of your question, but in ref, [3] of the attachment, the authors have claimed that they selectively have bonded U(IV) using modified naturally occurring product. In spite of the fact that most 'resins' used for separation are based on EDTA-like ligands, such as functionalization of polymers can be performed easy as an effort to achieve a high selectivity. 

In ref. [2], the authors have claimed that U(VI) can be bonded also selectively, using derivatives of the fulvic acid operating within the frame of a narrow range of pH values.

In ref. [1] we have performed a maximum representative literature research in the topic of the environmental speciation of radionuclides, despite the shown title of the book, because of we have correlated teh reliability of the quantum chemical parameters toward those ones for real environmental objects. 

So that the info in the attachment has involved literature research up to 01.2015, and most probably you may find something useful.

Did you already think of capillary electrophoresis? If I remember right, this should work for speciation of Actinoides.

Thank you for the answers, I will have a look. I found this paper where they use Dowex raisin to separate the species, followed by KPA analysis. I will attach the paper.  Anyone tried that? Or what is your opinion on this type of separation...

Ion exchange or extraction chromatography is the way to tackle this.  For isolating two species quickly and efficiently, you can use stacked columns to load only one species per column (e.g., species I is extracted on column I; species II is unretained on column I but is retained on column II).  However, you have not stated what is the chemical matrix of your sample.  This chemical matrix will drive the speciation of U(VI) / U(IV) in your sample, which will drive the selection of your column media. 

Mrs./Miss Novotnik,

The authors of the paper which you have provided, discussed that in fact using the Dowex (page 9230) there is unable to achieve selectivity. Bacause of, from chemical point of view, the coordination and protonaccepting behavior of this resin is in fact analogous to the EDTA. Please find a new attachment with the corresponding chemical diagrams and data. The resin has only a substituted phenyl ring added to achieve a polzmerization. But from phenyl we can expect only weak p-interactions, which as the authors have demonstrated, have small contribution to the selectivity of the resin.  

In fact, the authors is this paper have provided expectable conclusions about the low selectivity of this resin, like EDTA and largest series of ethylenediamine based resins. Such as results have been reported in ref. [1] and are shown in a figure (page 1 in the current attachment). As you can see, the presence of EDTA has resulted to complete coordination, but not selective one within the whole range of pH, which coordination prevent the adsorption onto inorganic minerals.

By contract, the employment of fulvic acid has shown a selective coordination behaviour, depending of pH.

If you have described the figures (page 2) in the current attachment (refs. [2]), there is shown that UIV, UVI and UIII have strongly distinguished binding affinity and coordination behavior, accounting for the same behaviour of UVI and [UO2]2+ ions (page 2, current attachment), however. Furthermore the mechanism of ligand exchange is different for the different complexes and experimental conditions. There are our theoretical data with a large set chemical  forms of U towards series of inorganic minerals. Currently we have under consideration in Journals the whole set of Lns and Ans and large distributed in the nature complexes, accompanied with selected experiments performed, but small set.

So that there is able to achieve a selective separation, but employing different molecular scaffold of the ligands (resings and s.o.), from the current largest set of commercially distributed resins. In this respect, the studies refs. 3 and 4 in my previouse attachment are meaningful, nevertheless that the authors have provided data only for UIV (ref. 3) and [UO2]2+ (ref. 4). There has not information for the competitive coordination behavior, depending of the oxidation state and experimental conditions, allowing to evaluate the coordination ability towards selectivity.           

Dr. O'Hara, thank you for your answer, I was also thinking of Ion chromatography. Our samples would be fresh lake waters. The answers of Dr. Ivanova where really helpful but also gave me a lot to think about. I guess the separation is going to be pretty hard to achieve. 

Dr. Ivanova, I cannot thank you enough for taking this much time and explaining everything to me, your posts were very insightful and also made me realize I was oversimplifying things. Hope I can apply some of your suggestions in my future research.