Charge is a fundamental property of macromolecules. However, new instruments and new methods have been needed to explore the role of charge in determining the structure, stability, and interactions of macromolecules. An apparatus is described here that is capable of performing equilibrium electrophoresis, electrophoretic mobility or diffusion measurements. This instrument acquires absorbance data from up to 512 positions along a quartz cell. The cell permits the establishment of an electric field along its length, while retaining macroions in the field of view. The prospects and limitations of using equilibrium electrophoresis for clinical applications are explored, particularly for characterizing macromolecular reagents. Applications are described for detecting charge heterogeneity, monitoring sample stability, and for determining the role of charge in molecular structure, stability and interactions. Because equilibrium electrophoresis provides little sample fractionation, the analysis of complex fluids requires the use of specific optical labels for discriminating components.
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