Determination of Polymer Effective Charge by Indirect UV Detection in Capillary Electrophoresis: Toward the Characterization of Macromolecular Architectures

Abstract

This work deals with the determination of polymer effective charge based on the sensitivity of detection in capillary electrophoresis using indirect UV detection. In this detection mode, the polyelectrolyte (solute) displaces a certain quantity of probe contained in the background electrolyte and having the same charge as the solute. This quantity of displaced probe is directly correlated to the effective charge of the solute. Contrary to other electrophoretic methods generally used for monitoring changes in effective charge, this methodology is not based on the effective mobility of the polyelectrolyte (i.e., migration times) but on the sensitivity of detection (i.e., peak areas). Experimental values of effective charge obtained for statistical copolymers of poly(acrylamideco-sodium 2-acrylamido-2-methylpropanesulfonate), for homopolymers of poly(diallyldimethylammonium chloride), poly(acrylic acid), and poly(metacrylic acid), are compared to the Manning theory of charge condensation. Interestingly, this methodology can be used for the characterization of macromolecular architecture since the effective charge of copolymers highly depends on the repartition of the charged monomers along the polymer chain. As an example, this methodology can easily distinguish statistical copolymers from diblock copolymers of similar chemical charge densities. Experiments were carried out on diblock copolymers of poly(acrylic acid)-bpoly(ethylene oxide) (PAA-b-PEO) and poly(methacrylic acid)-b-poly(ethylene oxide) (PMAA-b-PEO). The variation of the sensitivity of detection of statistically charged copolymers in the indirect UV mode with the chemical charge density is also discussed in detail.

Generalized polymer effective charge measurement by capillary isotachophoresis

“…For PGlu and PAMAMPS 10%, lower effective charges were obtained compared with the expected theoretical values. In the case of PAMAMPS copolymer, the lower experimental effective charge (z 1 ∼0.73-0.79 vs 1) was explained by a non-perfect statistical repartition of the charged groups [19] leading to rich AMPS sequences monomers within the polymer chain. This explanation was supported by the differences between reactivity ratios for the two monomers [33,43].…”

“…where c m,polymer is the mass concentration in copolymer, M 1 the molar mass of a charged monomer, M 2 the molar mass of the uncharged monomer and f is the molar fraction of charged monomers in the copolymer [19]. Further, f, also called the chemical charge density, is expressed as:…”

“…Different methods have been investigated for polymer effective charge determination including conductivity measurements [14], osmotic pressure [15], scattering techniques [16] and electrophoretic techniques [17][18][19][20][21][22][23][24][25]. Conductivity and osmotic pressure measurements are generally performed in the absence of additional salts (or at very low ionic strength), while neutron scattering techniques requires specific and restricted-access source of radiations.…”

“…A second group is basically relying on the Kohlrausch regulating function (KRF) [19] or on electroneutrality and electric current conservation [12,17,20], allowing a direct determination of the effective charge by capillary electrophoresis using indirect UV detection mode (IUV) [19] or by capillary isotachophoresis (ITP) using conductometric or UV-absorption detection [12,17,20]. The IUV method consists in determining the effective charge from the transfer ratio (i.e.…”

Polyelectrolyte multilayer coatings for the separation of proteins by capillary electrophoresis: Influence of polyelectrolyte nature and multilayer crosslinking

“…Polyelectrolytes are classified by families (polypeptide/polyamide, vinylic, polysaccharide, allylic, polyionene). ion-pair formation) and the polymer effective charge corresponds to the nominal (or chemical) charge [28,29]. On the contrary, when > 1, charge condensation occurs (ion-pair formation), so that the effective polyelectrolyte charge remains constant whatever the charge parameter [28,29].…”