Separation of poly(amidoamine) (PAMAM) dendrimer generations by dynamic coating capillary electrophoresis

The separation of compounds possessing amino groups (peptides, proteins, polyamino compounds) by capillary zone electrophoresis suffers from the interaction (sticking) of these solutes with the capillary wall. This sticking can result in the absence or incomplete separation of compounds or even in their retention in the capillary. Polyamidoamine (PAMAM) dendrimers are a class of spherical polymers with primary amino groups at the surface. These compounds can be separated reasonably well at acidic pH but not at neutral pH. A new method based on the dynamic coating of the capillary was developed for the separation of these compounds at pH 7.4. The method comprises separation in a fused-silica capillary (57 cm total length, 50 cm to the detector, ID 75 μm) and a background electrolyte consisting of a Tris-phosphate buffer (50 mmol/L, pH 7.4) and 0.05% (w/v) polyethyleneimine. This system is suitable for the separation of 7 generations of dendrimers (generations 0–6). The dynamic coating agent (polyethyleneimine) also improves the separation at acid pH.