Sodium dodecyl sulfate capillary electrophoresis of proteins in entangled solutions of poly(vinyl alcohol)

A novel polymer network is described for efficient sieving of sodium dodecyl sulfate (SDS)-protein complexes: poly(vinyl alcohol) (PVA; average M_r 133 000). The entanglement threshold of these solutions was found to be at 3% (w/v) PVA. Solutions from 4 to 6% PVA offer excellent resolution in the 14 400-94 000 protein molecular mass interval. Ferguson plot analysis showed that the separation is indeed based on mass discrimination, as it should in SDS electrophoresis, with extrapolated (at 10% polymer) limit values of mobility for all particles in the range (2.34-2.87) · 10^-8 m² V^-1s^-1. The advantages of PVA are full transparency in the UV region down to 200 nm and extremely low viscosities (e.g., a 5% PVA solution has a viscosity 25 times greater than that of buffer at 30°C). A unique wall effect was found, by which, on decreasing the inner diameter of the capillary from 75 to 25 μm, the apparent entanglement threshold was shifted to extremely dilute PVA solutions, since in 25-μm capillaries efficient sieving was obtained below 1% PVA, i.e., at concentrations well below the entangled regime. It is hypothesized that residual, free silanols present (even in a coated capillary) act as nucleation sites for H-bond formation and aggregation of free PVA molecules.