Particle-size-distribution analyses have been carried out on a wide variety of suspended organic and inorganic particulates using a new technique of time-delayed exponential force-field sedimentation field flow fractionation (TDE-SFFF). Analyses for particles In the <0.01-1.0 pm range have been made in less than 30 min. Relative to constant-field SFFF, the TDE-SFFF method drastically decreased analysis time and Improved detection sensitivity while maintaining adequate resolution for convenient and accurate particle size distribution analyses. A description Is given of TDE-SFFF equipment operating to 20 000 rpm or about 50 000 gravities. Also described is the computer software utilized for handling data and certain Instrumental control functions.High-resolution separations of a wide range of suspended particulates and dissolved macromolecules can be performed by sedimentation field flow fractionation (SFFF). SFFF is carried out with a single, continuously flowing mobile phase in a very thin, open channel under the influence of an external centrifugal force field. Due to the influence of this field, sample retention is obtained by the redistribution of components from fast-to slow-moving mobile-phase streams. This "one-phase-chromatography" method produces high-resolution fractograms of particles eluting in the order of increasing size for particles of equal density. Relative to operation (1-3) at constant rotor speed, separations carried out by programming a decrease in field strength span a much wider particle-size range per unit time. Simple linear (1) and simple exponential field-programmed (4) SFFF have provided certain advantages in obtaining SFFF data for convenient particle-size distribution calculations. However, as discussed in this paper, the use of time-delayed exponential field-programmed SFFF, designated as TDE-SFFF (5), is an even more desirable approach.This paper provides a description of the equipment used for TDE-SFFF, the software utilized for computer-control of the hardware, and the software for data handling. Finally, we present typical applications of the TDE-SFFF method for a variety of particle-size-distribution analyses. EXPERIMENTAL SECTIONApparatus. The present SFFF equipment is an improved version of that described previously (4). The general configuration of the SFFF equipment is shown schematically in Figure 1. Precise mobile-phase flow rates were provided by a microprocessor-operated DuPont Model 850 liquid chromatographic solvent-metering module (DuPont Instrument Products Division, Wilmington, DE). The internal pulse-damper of this pump provided sufficient back-pressure for proper check-valve operation and accurate solvent delivery to the open SFFF channel of low flow resistance.The main SFFF separating system consisted of a rotating face seal and the SFFF channel, housed within the rotor of a Sorvall Model RC-5 centrifuge (DuPont Instrument Products Division, Wilmington, DE). Shown schematically in Figure 2, the rotating face-seal permits mobile phase to be pumped in and out of t...

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Basle Information obtained from flow field-flow fractionation (FIFFF) experiments are diffusion coefficients of molecular components or the Stokes diameter of colloidal particles. To measure the molecular weights (MW) and molecular weight distributions (MWD) of polymers, calibration with known standards previously was required. This study describes a new FIFFF method for finding MW and MWD by converting diffusion coefficients using available Mark-Houwlnk constants for polymers. Appropriate software was developed to calculate and plot the MWD of polymer systems. Water-soluble polymers serve as model systems to Illustrate the quantitative capability of this low-shear characterization method. Use of exponentially-decayed (cross-flow) force fields permits a wide MW range to be accessed with a single experiment In a practical operating time. FIFFF Is a useful method for characterizing synthetic and natural polymers and many organic and Inorganic colloidal particles.

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