Analytical Measurements of Ultracentrifugal Sedimentation

Abstract

SEDIMENTATION in the ultracentrifuge has so far been followed quantitatively only by optical methods, depending upon the absorption or refraction of light by the substances studied. Even though they have been worked out to a high degree of accuracy, these methods for many important problems need to be supplemented by some procedure allowing chemical tests to be performed in the same run. For example, in a mixture of an enzyme or an antibody with its accompanying impurities, we do not know α priori the relationship between optical properties and the amount of active substance, and we cannot therefore definitely state which of the optically observed components in the mixture, if any, carries the activity. As the amount of substances of this kind in most cases can be defined only by an action measured by analytical methods, their sedimentation should be computed from analysis of samples taken out of the ultracentrifugal cell. In this laboratory^1,2 and elsewhere³, several attempts have been made to take out samples of the ultracentrifuged solutions after concluding an experiment, but the arrangements have not been sufficiently perfect to allow quantitative application.