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

Abstract

To gain insight into the mechanisms of size-dependent separation of microparticles 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(-1). Size-dependent electrophoretic migration of polystyrene particles in CZE was shown to be an explicit function of kappaR, where kappa(-1) and rare the thickness of electric double layer (which can be derived from the ionic strength of the buffer) and particle radius, respectively. Particle mobility depends on kappaR in a manner consistent with that expected from the Overbeek-Booth electrokinetic theory, though a charged hairy layer on the surface of polystyrene latex particles complicates the quantitative prediction and optimization of size-dependent separation of such particles in CZE. However, the Overbeek-Booth theory remains a useful general guide for size-dependent separation of microparticles in CZE. In accordance with it, it could be shown that, for a given pair of polystyrene particles of different sizes, there exists an ionic strength which provides the optimal separation selectivity. Peak spreading was promoted by both an increasing electric field strength and a decreasing ionic strength. When the capillary is efficiently thermostated, the electrophoretic heterogeneity of polystyrene microspheres appears to be the major contributor 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 even dominate it.

Determination of individual microsphere properties by capillary electrophoresis with laser-induced fluorescence detection

“…Multiple reports have clearly confirmed that polystyrene latex microspheres have an intrinsic electrophoretic mobility that makes them amenable to analysis by CE [7,11]. This fact is confirmed in Fig.…”

“…According to these theories, the electrophoretic mobility of particles in a CE regime cannot be described in the Hückel limit that is usually applicable to ions made of a few atoms. Instead, it is necessary to define the electrical charge as found at the shear surface of the particle which defines an electrostatic potential (z potential) [11]. For instance, for a nonconducting sphere with z potential up 25 mV, the electrophoretic mobility is expressed as:…”

“…For values lower than 25 mV, the z potential will increase with R until kR exceeds 20 where this potential becomes practically constant [11]. The factor f(kR) known as the Henry function [11] varies from 1 at kR ,, 1 (the Hückel limit) to 1.5 at kR .. 1 (the Smoluchowski limit). This function increases monotonically between the kR range 1-100.…”

“…By minimizing the contribution to broadening related to the analytical procedure, several researchers have reported that electrophoretic heterogeneity dispersion resulting from either size or surface composition is the ultimate limit in band broadening [7,9,11]. Unfortunately, in these reports the conclusions are based on the combined response of millions of particles which typically are convolutions of the instrumental response time and the number of events being detected at a given time.…”

Capillary electrophoresis – mass spectrometry: 15 years of developments and applications

“…CE is a relatively nonperturbing method allowing the structure-dependent electrophoretic separation of monodisperse or polydisperse mixtures of small molecules [339][340][341], macromolecules [342][343][344][345], polymers [346][347][348][349] and colloids [350], up to nanoparticles [351][352][353][354] and liposomes [355], even bacteria [350,356] and viruses, in various modes of gentle separation techniques using nonaqueous or aqueous buffers with coated or uncoated capillary columns. The small volume of the analyte needed in CE experiments has made possible the measurement of the cellular contents (native proteins [357], specific fluorescent-labelled or-induced proteins [358], metabolites), the monitoring of single cells [359,360] or bacteria communications [361].…”