(9g) Electrofocusing Small Organic Ions

Traditional electrofocusing methods, i.e., isoelectric focusing, are very difficult to use with ionic species that don't have a defined isoelectric point, for example, pharmaceuticals. However, these low molecular weight ions can be separated and concentrated using alternative focusing methods like dynamic field-gradient focusing (DFGF). The problem that arises with small molecules is that DFGF traditionally uses a dialysis membrane to segregate the separation channel from the electrodes and so ions with molecular weights less than about 1000 will leak through membranes with molecular weight cutoffs as low as 100.

This paper describes our efforts to design a column and develop protocols suitable for electrofocusing small, non-amphoteric ions by eliminating the membrane and installing the electrodes directly into the separation channel. Doing this causes three major problems: (1) gas evolution at the electrodes, (2) pH changes adjacent to the electrodes, and (3) solute oxidation-reduction reactions on the electrode surfaces. A combination of experiment and simulation was used to determine whether these problems could be eliminated by changing the design of the separation channel and the protocols used to electrofocus low molecular weight solutes.