Development of a combined ultra- and diafiltration technique for use in speciation analysis of protein-bound cadmium in plants

Summary A combination of stepwise ultrafiltration with subsequent diafiltration for application in speciation analysis of aqueous biological samples is presented which allows the determination of distribution patterns without changing the native binding forms (species). This is possible without additional buffers and, furthermore, is less time consuming than conventional ultrafiltration. It is shown that preliminary statements about binding forms can be made by an optimization of this technique for the separation of an individual sample by recording and interpreting the filtration profile. The developed filtration technique is used for the evaluation of distribution patterns of proteins and cadmium species of an extract from self-cultivated dwarf runner beans to which cadmium was offered for uptake. According to these investigations, the cadmium species are present overwhelmingly in the molecular weight range >30,000 g/mol (61% of the total cadmium content).