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 electrophores is equipment. The capillary is first filled with, e.g., a liquid of kn own viscosity and then the solution under analysis is pumped through i t at a constant pressure drop and constant temperature. The migration time of the boundary between the two liquids from the injection port t o the detector is carefully measured and the experimental data are ent ered in a derived modified Poiseuille equation for calculating the unk nown viscosity. Viscosities of small analytes (e.g., sucrose solutions ) and of macromolecular solutions (e.g., methylcellulose) could be ass essed with a precision of the order of 3%. The boundary between the tw o liquids is usually detected by refractive index gradients, even in t he presence of non-UV-absorbing species. With very minute refractive i ndex variations, the boundary is easily detected by spiking one of the two solutions with traces of a strongly UV-absorbing compound (e.g., riboflavin).