Direct determination of macromolecular charge by equilibrium electrophoresis

Charge is a fundamental property of macromolecules in solution. However, estimation of the apparent charge on polyions has confounded science for decades. Presented here is a general method to determine directly the apparent charge on a polyion, regardless of its size or shape. This new method uses equilibrium electrophoresis, a procedure in which opposing solute flows from electrophoresis and from diffusion balance everywhere as the system reaches a steady-state distribution. The method uses only small quantities of materials, is nondestructive, and requires only simple, inexpensive instrumentation. Here we describe a prototype apparatus, demonstrate the phenomenon, and present experimental examples of the procedure.