A new method is presented for measuring the molecular properties of an unfractionated solution of macromolecules. Sample aliquots spanning a range of concentrations are injected sequentially into a stream of solution and flow towards the detectors. Each aliquot produces, thereby, an effective "peak" whose elements correspond to different concentrations of the diluted aliquot. The weight averaged molar mass, the mean square radius, and the second virial coefficient of the macromolecules in solution are derived from an analysis of the angular and concentration dependence of the scattering signals throughout the corresponding peaks. In contrast to earlier on-line methods, better accuracy is achieved, while using a smaller quantity of sample. A similar method for determining cross virial coefficients between two distinct species of macromolecules is also presented.
A method and apparatus is described by which means molecules in suspension may be characterized in terms of the size and mass distributions present. As a sample solution is separated by centrifugal means, it is illuminated at a particular radial distance from the axis of rotation by a fine, preferably monochromatic, light beam. Despite the high resolution of such devices, a key problem associated with most separators based upon use of centrifugal forces is the difficulty in deriving the absolute size and/or molar. mass of the separating molecules. By integrating means to detect light scattered, over a range of scattering angles, from samples undergoing centrifugal separation, molecular sizes in the sub-micrometer range may be derived, even in the presence of diffusion. Adding a second light beam at a displaced rotational angle, preferably of an ultraviolet wavelength, that intersects the sample at the same radial region as the first beam permits determination of the molecular concentration at that region. Combining the light scattering data with the associated concentration permits the determination of the associated molar mass. In a preferred embodiment, the light beam and detectors may be controlled to scan synchronously the sample radially during separation.