Selective absorption and scattering of light by solutions of macromolecules and by particulate suspensions

For particulate suspensions and for solutions that scatter light measurably the total absorbance A generally contains contributions due to specific absorption ( A a) and scattering of light ( A s). The quantity A s is closely related to the turbidity τ. In general, spectrophotometry of such systems requires proper modification of the spectrophotometer used in order to permit accurate determination of the absorbance A and of the derived quantities A a and A s. Apparent deviation from Beer's law in such systems is often due to inappropriate experimental technique. After a discussion of the parameters that determine the intensity of light scattered by solutes, an account is given of the experimental precautions to be taken for determination of the absorbance of light scattering suspensions and solutions and of techniques for correcting absorbance spectra for scattering of light. Measurement of the turbidity is briefly confronted with determination of the scattering ratio i 90°/ I o and the impact of erroneous turbidity measurements on derived molecular parameters is disccused