AUTOMATED PARTICLE ELECTROPHORESIS - MODELING AND CONTROL OF ADVERSE CHAMBER SURFACE-PROPERTIES

Electrophoretic analysis of colloidal particles is adversely affected by a host of surface phenomena, including electroosmosis, phase wall w etting, and sample or air bubble adsorption. Neutral, hydrophilic poly mer coatings control such phenomena on a variety of surfaces. Poly(eth ylene glycol)-poly(ethylene imine) (PEG-PEI) conjugates significantly reduce electroosmosis and positively control adsorption and wetting in the glass sample chambers (5 mm x 3 mm x 1 mm i.d.) employed in a rep resentative commercial electrophoresis apparatus (Coulter DELSA 440). The reduction in electroosmosis (e.g., 80% in 7.5 mM solution at pH II ) was similar to that exhibited by coated 2-mm-i.d. quartz capillaries in a Rank MK I manual apparatus, PEG-PEI coatings significantly reduc e electroosmosis over a wide range of pH (2-11) and ionic strength (1- 100 mM) and can be stable for weeks under normal laboratory conditions , They greatly enhance ease of operation and accuracy (sample mean ele ctrophoretic mobility +/- SD) of the DELSA 440. The latter results fro m reduced electroosmosis now profile gradients near the chamber center -axis stationary levels, where particle mobility is typically measured . Such flow profiles may also be affected by chamber wall surface asym metries. A hydrodynamic description of electroosmotic fluid now in rec tangular chambers was adapted in order to analyze the propagation of e rrors due to both nonideal focusing and chamber surface asymmetry. The analysis indicated that the accuracy of rectangular chambered devices may be improved by measuring particle mobility at stationary levels d ifferent than chamber center axes. As a result, some rectangular chamb ers may confer accuracy advantages over cylindrical chambers.