Characterization of chromatographic silica beads by micro-thermal field-flow fractionation

Micro-thermal field-flow fractionation (micro-TFFF) was used to characterize silica based chromatographic beads within the diameter range from 3 to 10 mum. The main goal of this study was to demonstrate that silica particles that sediment in water suspensions and are usually separated by gravitational field-flow fractionation (GFFF), can be retained more effectively under the conditions of micro-TFFF. It has been found, that the retentions of all studied particles substantially increased when the temperature drop, DeltaT, across the micro-TFFF channel was applied, in comparison with the retentions when only the gravitation was acting as an effective field at DeltaT = 0 K. This finding confirmed that micrometer size and high-density silica particles exhibit a positive thermal diffusion coefficient. Various operational conditions were tested up to extreme temperature drop, DeltaT = 80 K, at the temperature of the cold wall T = 300 K. As a result, the time of micro-TFFF analysis can be as short as 10 min. The samples were also characterized by scanning electron microscopy (SEM). The comparison of the results of micro-TFFF and SEM showed good agreement of the mean particle sizes and of the particle size distributions (PSD) estimated from the SEM pictures with the peak retentions, widths, and shapes of the micro-TFFF fractograms. Micro-TFFF was found as a rapid and easily applicable method for the characterization of the mean particle size and PSD of the chromatographic beads. This is an important conclusion because micro-TFFF can, thus, become a convenient and inexpensive analytical tool for the quality control of the uniformity of chromatographic beads, which determines the efficiency of the packed columns.