Abstract: The systems and methods of the invention provide for sample holders for centrifuges that include a channel structure having a sample channel and an overflow channel. The sample channel and the overflow channel are configured such that any excess sample flows into the overflow channel thereby maintaining a constant sample level in the sample channel. In other aspects, the invention provides for centrifuges comprising sample holders having a plurality of channel structures. In still other aspects, the invention provides for methods of using the sample holder and methods for detecting species in a sample using luminescence based measurement techniques.

Abstract: A method of (and apparatus for) determining charge on protein or other macromolecule. The method involves providing two spaces, each containing buffer (e.g., water or saltwater), establishing a volume (a cuvette herein) between the two spaces, which volume contains the macromolecule in a solution that includes the buffer that establishes the pH of the solution (typically a pH of 0 to 12) and that further includes a gelling agent to inhibit convection. The macromolecule is confined to the volume (the cuvette); there is electrical continuity through the volume from the buffer in one space to the buffer in the other space; and there is flow of small molecules (e.g., of the buffer) from one space to the other through the volume. There is also external flow of buffer between the two spaces to maintain constancy of ionic contact therein as well as constancy and equality of liquid level, but no electric current flow between the spaces through or along the buffer in the external flow.