Extension of Sedimentation/Steric Field-Flow Fractionation into the Submicrometer Range: Size Analysis of 0.2-15-µm Metal Particles

Sedlmentatlon/sterlc field-flow fractionation (FFF), a rapid method for the high-resolution separation and characterization of >1-µm-diameter particles, can be extended well into the submicrometer size range providing the sterlc Inversion (or transition) diameter 4, normally about 1 µm, is significantly lowered. To better accomplish this, a means has been developed to predict 4 based on normal mode retention theory and sterlc mode calibration plots. By applying a high field strength, 4 can be systematically reduced below 1 µm and sterlc FFF analysis extended down to the modified 4 value. To offset the increased elution time associated with the smaller 4, channel thickness and breadth are reduced and high channel flow rates utilized. The high flow rates and slow flow (rather than stop-flow) injection reduce sample losses at the channel wall. The above concepts were verified using polystyrene latex standards. Application was made to samples of gold, palladium, silver, and copper particles. A single sterlc calibration plot, obtained by electron microscopy for gold particles, was applied to the size analysis of various metals using the density compensation method. For these runs d₁~ 0.2 µm. (Much smaller sizes than 4 can be analyzed by normal mode FFF but then larger sizes are excluded.) Analysis times ranged from 1 to 12 min depending on the smallest particle size.