Elementary biophysics: selected topics elementarybiophy00epst Year: 1963 78 METHODS FOR DETERMINING MOLECULAR SIZE AND SHAPE Recent developments of the electrophoretic technique include placing the solution on long strips of special filter papers in a moist atmosphere, and applying the electric force across the ends of the paper strip. The separation of the constituents is then achieved simply by using a scissors, and the constituents may then be eluted from the paper in suitable buffers. (b) Static methods If the particles are stationary, then the physical agent for extracting information h
Elementary biophysics: selected topics elementarybiophy00epst Year: 1963 78 METHODS FOR DETERMINING MOLECULAR SIZE AND SHAPE Recent developments of the electrophoretic technique include placing the solution on long strips of special filter papers in a moist atmosphere, and applying the electric force across the ends of the paper strip. The separation of the constituents is then achieved simply by using a scissors, and the constituents may then be eluted from the paper in suitable buffers. (b) Static methods If the particles are stationary, then the physical agent for extracting information has to move into and out of (or at least away from) these particles. Thus, we are led to examine the irradiation of particles by visible light, ultraviolet and x-radiation, and various charged elementary particles. Visible light scattering. If a particle is very tiny, light waves scattered off its front and rear will be so nearly in the same phase that they scarcely interfere with each other in the sense of waves reinforcing or cancelling each other. If, as indicated in Fig. 36, the particle is compara- ble in size to the wavelength of light being used, then the wave scattered Eye or photographic film Fig. 36. A light beam whose wavelength is comparable to the dimensions of the scattering particle is reflected in various directions by the particle. The bottom wave travels about a half wavelength more than the middle wave be- fore being reflected, so that it is possible to find a direction, as indicated, in which the eye or a light-sensitive film will record that the reflected beams arrive out of phase, so that there is a cancellation of beams. Other directions could be found in which the beams arrive so that thev reinforce each other.
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