CAPILLARY ELECTROPHORESIS INSTRUMENTATION AS A BENCH-TOP VISCOMETER

A simple and reliable method is proposed for measuring the viscosities of different solutions by using standard capillary zone electrophoresis equipment. The capillary is first filled with, e.g., a liquid of known viscosity and then the solution under analysis is pumped through it at a constant pressure drop and constant temperature. The migration time of the boundary between the two liquids from the injection port to the detector is carefully measured and the experimental data are entered in a derived modified Poiseuille equation for calculating the unknown viscosity. Viscosities of small analytes (e.g., sucrose solutions) and of macromolecular solutions (e.g., methylcellulose) could be assessed with a precision of the order of 3%. The boundary between the two liquids is usually detected by refractive index gradients, even in the presence of non-UV-absorbing species. With very minute refractive index variations, the boundary is easily detected by spiking one of the two solutions with traces of a strongly UV-absorbing compound (e.g., riboflavin).