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

The particle size distributions of various silica support materials fo r high performance liquid chromatography (HPLC) and size exclusion chr omatography (SEC) were obtained using flow/hyperlayer field-flow fract ionation (Fl/Hy FFF), a form of flow FFF. The experimental procedure f or each material required only 3-6 minutes. The resulting fractograms (representing detector response as a function of time) were mathematic ally treated to yield particle size distribution curves. Unlike most t echniques, Fl/Hy FFF yields particle sizes free of any assumption abou t particle density or porosity. Approximate mean particle diameters an d polydispersities were estimated directly from the fractograms and co mpared to those more correctly calculated from the size distribution c urves. The importance of specifying the type of mean particle diameter (such as area, mass, and number averages) being reported is illustrat ed. The good agreement between the FFF number-weighted size distributi ons and those obtained by scanning electron microscopy demonstrates th e usefulness of Fl/Hy FFF for the rapid and accurate characterization of chromatographic silicas.