A new reference sample for microelectrophoresis

Abstract

Syntheses of a reference particle dispersion stabilized sterically in an aqueous medium without any electrostatic effects and measurements of the zeta (ζ)-potential using the reference dispersion as a standard were performed under various experimental conditions. It became apparent that the dense adsorption layer of hydroxyl propyl cellulose (HPC), with a lower critical solution temperature (LCST), formed on latex particles with a low surface charge density ( σ 0 < 1 μC cm 2 ) at temperatures higher (60–80°C) than the LCST, plays a role in completely shielding the electrostatic effect arising from the surface charge on the bare particles. There was a critical amount of HPC adsorption above which the ζ-potential of the HPC-coated particles becomes really zero. Such reference particles with zero ζ-potential allow us to determine the electrophoretic mobility of unknown samples at the one-half depth in the electrophoretic cell by subtracting the mobility of the reference sample at the same level. Also, the ζ-potential of the cell wall can be easily determined from the mobility of the reference sample, because the apparent velocity profile of the reference sample indicates the liquid flow velocity profile in the cell. Determination of the ζ-potential for amphoteric latices and Agl sol using this new procedure indicates that the reference dispersion prepared here can be applied widely for many colloid particles dispersed in media of a wide range of pH and salt concentrations. Furthermore, the stability of the reference particles has been manifested in a few specific examples.