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An Evaluation of Zonal Centrifugation as a Research Tool in Soil Science: I. Methodology¹

ABSTRACT

The methodology involving zonal centrifugation of clay sized mienrals through density gradients is presented. Various aspects of the procedure such as gradient solvents, formation of the gradient, dispersing agents, and methods of band removal are discussed. The parameters of centrifugal force, saturating cation, and particle size were evaluated as to their effect on time and isopycnic banding location within the gradient. It was concluded that an ultracentrifuga is required (a force field greater than 623 g) to band isopycnically clay particles of < 0.2 microns in diameter. The saturating cation influenced banding of 2:1 expandable layer silicates to a greater degree than 1:1 layer silicates, and the spatial relationshp of the expanding layer silicate associated with specific cation saturation played a larger role in banding than differences in atomic weight among the saturating catons.

¹ Research sponsored by teh US Atomic Energy Commission under contract with the Union Carbide Corp.

² Senior staff scientists, Ecological Sciences (first author) and Health Physics Divisions, Oak Ridge National Lab., Oak Ridge, Tenn. 37830.

Received for publication July 16, 1971. Accepted for publication December 22, 1971.