Capillary zone electrophoresis of sub-mu m-sized particles in electrolyte solutions of various ionic strengths: Size-dependent electrophoretic migration and separation efficiency

To gain insight into the mechanisms of size-dependent separation of micropa rticles in capillary zone electrophoresis (CZE), sulfated polystyrene latex microspheres of 139, 189, 268, and 381 nm radius were subjected to CZE in Tris-borate buffers of various ionic strengths ranging from 0.0003 to 0.005 , at electric field strengths of 100-500 V cm-l. Size-dependent electrophor etic migration of polystyrene particles in CZE was shown to be an explicit function of kappaR, where kappa (-1) and rare the thickness of electric dou ble layer (which can be derived from the ionic strength of the buffer) and particle radius, respectively. Particle mobility depends on kappaR in a man ner consistent with that expected from the Overbeek-Booth electrokinetic th eory, though a charged hairy layer on the surface of polystyrene latex part icles complicates the quantitative prediction and optimization of size-depe ndent separation of such particles in CZE. However, the Overbeek-Booth theo ry remains a useful general guide for size-dependent separation of micropar ticles in CZE. In accordance with it, it could be shown that, for a given p air of polystyrene particles of different sizes, there exists an ionic stre ngth which provides the optimal separation selectivity. Peak spreading was promoted by both an increasing electric field strength and a decreasing ion ic strength. When the capillary is efficiently thermostated, the electropho retic heterogeneity of polystyrene microspheres appears to be the major con tributor to peak spreading. Yet, at both elevated electric field strengths (500 V/cm) and the highest ionic strength used (0.005), thermal effects in a capillary appear to contribute significantly to peak spreading or can eve n dominate it.