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|Macromolecules 2011, 44, 3062-3072 Macromolecules ARTICLE (7) There is substantial band broadening caused by some factors not well understood at this moment. An in-depth investigation is needed in order to improve TGIC resolution capability.

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Chromatographic resolution and analysis accuracy can be seriously affected by broadening of very sharp bands associated with both high-performance size-exclusion chromatography and other liquid chromatography methods using less than 5 micron particles. The effect on column plate count by extra-column band broadening from injection systems, detectors, connectors and "guard" columns is discussed and exemplified with experimental data. The special cases of tailing and doublet peaks for a single species are investigated. These effects are eliminated by a special sample injection technique. Computer simulation studies demonstrated that serious errors can result from calculating column plate count with non-Gaussian peaks. The maximum allowable peak tailing is suggested and a new method for quantitating peak skew is proposed.

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...