[30] UV absorption and circular dichroism measurements on light scattering biological specimens; fluorescent cell and related large-angle light detection techniques

This chapter describes a set of new instrumental concepts designed to obtain ultraviolet absorption and circular dichroism (CD) spectra of intensely scattering specimens, such as suspensions of virus, chromatin, chromosomes, nuclei, cells, and numerous other biological structures. The need for special techniques arises in connection with sample particles whose characteristic dimensions are within about one order of magnitude of the measuring light wavelength. The suspensions of such large particles will be likely to scatter light outside the detection region of a conventional spectrophotometer or circular dichrograph. In absorption measurements, the scattering will add to the true absorption of the sample. The most common instrumental means of eliminating scattering distortion in absorption measurements has been to enlarge the solid angle of detection for light-scattering samples. As all other devices for experimental light scattering corrections, the fluorescent scattering cell has the effect of increasing the solid angle of detection so that scattered light will not miss the detector and register as absorption.