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Interpretation of Schlieren Density Gradient Photographs

John Innes Institute, Colney Lane Norwich, NOR 7OF England

Equilibrium density gradient sedimentation is a well-established biochemical procedure. It is often convenient to use the Schlieren optical system to record the results of experiments using this technique. This optical system produces a photographic representation of the first derivative of the refractive index of the cell contents with respect to distance along the cell, which approximates to the concentration gradient. At equilibrium, the shape of a ‘band’ of a monodisperse macro-molecular species is approximately Gaussian because of diffusion away from the true equilibrium position. Such distributions are not normally truly symmetrical, but this fact does not invalidate the results or discussion presented later.

If two or more components are present then the total concentration distribution will be the sum of the individual distributions, and the Schlieren pattern will represent the first derivative of the sum.

accepted 25 October 1972.