Direct digital data capture for sedimentation velocity experifments using UV/VIS optics

Abstract

We developed a substitute for the dynography/multiplexer unit of the Beckman Model E Analytical Ultracentrifuge (AUC) consisting of a high-speed analog-to-digital converter and a personal computer. With this combination, we determine directly the intensity of light pulses measured at the photomultiplier. The computer program is written in the C + + programming language under DOS. It measures peak heights, relates them to the cell numbers they belong to, calculates optical densities from sample and reference sector, and displays the optical densities as a function of radius on the computer screen. Thus, it is possible to measure simultaneously all five concentrations that can be carried by the six-hole rotor of the Beckman Model E AUC during one scan. A multiplexer or flash lamp is no longer necessary. After a short description of the method, some general comments on requirements of sedimentation velocity experiments and on noise problems are made. The hardware and software for direct digitizing is presented and a further enhancement is proposed using a high-speed, two-channel recording system and one additional photomultiplier recording the primary intensity.