Abstract: A free floating plastic channel for sedimentation field flow fractionation is suspended in a centrifuge rotor filled with a compensating liquid. The channel is constructed of a plastic central hub assembly fitted with a plastic outer ring preferably having a lower density than the hub. The outer ring contains a shallow channel on its radially inner surface and is interference-fitted to the inner ring to insure a liquid tight seal at zero force field. With the liquid totally surrounding the hub-outer ring assembly, stresses on the plastic parts are essentially equalized even under high force fields and leakage from the channel at the hub-ring interface is greatly reduced.

Abstract: The method described is useful in field flow fractionation techniques for reducing separation times and improving the convenience and accuracy of measuring sizes or molecular weights of particulates. In field flow fractionation, the particulates (particles or macromolecules) are subjected to a force field and a mobile phase while passing through a flow channel. This field strength is decreased exponentially as a function of time. Alternatively the flow velocity is increased exponentially as a function of time. The initiation of the change in field strength or flow velocity may be delayed a period of time. If this time delay is made equal to the time constant of the exponential decay, the range of particulate retention time that is linearly related to the logarithm of the particle size or molecular weight is increased.An apparatus for implementing the method is also described and teaches the use of a function generator for providing the desired exponential decay and delay time.

Abstract: A long, thin annular belt-like channel is designed for use in sedimentation field flow fractionation. The channel has a generally rectangular cross section and a width to thickness aspect ratio lying in the range of 3-50 to 1. The channel may be formed of a flattened capillary tube. The ratio of the thickness of the channel to the characteristic height of the particles to be separated is greater than 5 to 1.

Abstract: A long, thin annular belt-like channel is designed for use in sedimentation field flow fractionation. This channel, which may be contained in the rotor of a centrifuge, has a generally rectangular cross-section. It has an inlet positioned to introduce particulates (includes particles and/or macromolecules) approximately at the radial distance from the outer wall that is the equilibrium distance resulting from the average force field exerted on each particulate by the centrifugal force field and by the opposing normal diffusion forces due to Brownian motion. An outlet for the channel is similarly located. A modified design tapers the inlet and outlet.

Abstract: Disclosed herein is a resolving zone for a chromatograph comprising a plurality of porous, silica macroparticles chosen to provide the resolving zone with a bimodal pore distribution, the average pore size for each mode being such that the linear portions of the molecular weight calibration curve for each pore size in the bimodal distribution are nonoverlapping and the pore volume of each mode being such that the aforesaid linear portions are substantially parallel. The macroparticles can be either totally or superficially porous. The resolving zone can be composed of either a plurality of macroparticles each having a bimodal pore distribution or a plurality of macroparticles having one pore size distribution and a plurality of macroparticles having another pore distribution.

Abstract: A process for preparing a low-cost silica packing for chromatography is disclosed. The process involves spray-drying an aqueous silica sol containing from 5 to 60 weight percent silica, to form porous micrograins having a dense packing, acid-washing the porous micrograins, and sintering to effect a 5 to 20% loss in surface area.

Abstract: Disclosed herein is a powder of discrete, macroporous, microspheroids, each having an average diameter in the range of 2 to 50 microns and each composed of a plurality of large colloidal particles joined and cemented together at their points of contact by 1 to 10% by weight of non-porous, amorphous silica. These microspheroids have a high degree of mechanical stability and a surface area between about 80 and 110% of that of the large colloidal particles. Also disclosed is a process for the manufacture of this powder.