RAPID SIZE CHARACTERIZATION OF CHROMATOGRAPHIC SILICAS BY FLOW FIELD-FLOW FRACTIONATION

The particle size distributions of various silica support materials for high performance liquid chromatography (HPLC) and size exclusion chromatography (SEC) were obtained using flow/hyperlayer field-flow fractionation (Fl/Hy FFF), a form of flow FFF. The experimental procedure for each material required only 3-6 minutes. The resulting fractograms (representing detector response as a function of time) were mathematically treated to yield particle size distribution curves. Unlike most techniques, Fl/Hy FFF yields particle sizes free of any assumption about particle density or porosity. Approximate mean particle diameters and polydispersities were estimated directly from the fractograms and compared to those more correctly calculated from the size distribution curves. The importance of specifying the type of mean particle diameter (such as area, mass, and number averages) being reported is illustrated. The good agreement between the FFF number-weighted size distributions and those obtained by scanning electron microscopy demonstrates the usefulness of Fl/Hy FFF for the rapid and accurate characterization of chromatographic silicas.