Size distribution of marine submicron particles determined by flow field-flow fractionation

Flow field-flow fractionation (flow FFF) with power field-strength programm ing was used to size fractionate submicron particles (colloids) in coastal seawater. All analyses used filtered seawater as carrier solution to preser ve the native chemical environment of the colloids. Our fractograms show co lloid size distributions with major peaks centered at 50 to 60 nm for sampl es that were size fractionated immediately following the preconcentration s tep. Preconcentrated samples that had aged for 2 to 5 d revealed the presen ce of an additional larger sized particle (or aggregate) peak with indeterm inate size. Errors in colloid sizing may result if the physical and chemica l behaviors of the particle size standards are not mimicked by those of the colloids during separation in the flow FFF channel. Particle detection usi ng absorbance meters, such as the ultraviolet (UV) detector used here, grea tly underestimates the contribution of smaller particles (ca. <100 nm) due to the exceedingly small optical efficiency of particles within this size-r efractive index domain.