Chromatographic separation and characterization of hydrolyzed Cr(III) species

Both macroscale and microscale methods to separate hydrolyzed Cr(III) species from acidic to near-neutral pH solutions have been developed. The macroscale approach is based on ion exchange, and involves separating monomeric, dimeric, trimeric, tetrameric, and higher order Cr(III) oligomers from such solutions using a gradient elution with increasing cationic charge. With this approach, the concentration of a given fraction can be maximized, and complete resolution between these species can be achieved. In addition, complete recovery of Cr(III) from the column is achievable. For the microscale approach, capillary electrophoresis with indirect detection is used to isolate and uniquely identify the same smaller oligomers and a fraction of larger Cr(III) species that are not uniquely identified. Capillary electrophoresis also provides indirect structural information for the Cr(III) trimer, suggesting that it exists in a triangular configuration rather than as a linear species. These methods are described in detail, and possible applications are discussed.