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

Flow field-flow fractionation (flow FFF) with power field-strength programming was used to size fractionate submicron particles (colloids) in coastal seawater. All analyses used filtered seawater as carrier solution to preserve the native chemical environment of the colloids. Our fractograms show colloid size distributions with major peaks centered at 50 to 60 nm for samples that were size fractionated immediately following the preconcentration step. Preconcentrated samples that had aged for 2 to 5 d revealed the presence of an additional larger sized particle (or aggregate) peak with indeterminate size. Errors in colloid sizing may result if the physical and chemical behaviors of the particle size standards are not mimicked by those of the colloids during separation in the flow FFF channel. Particle detection using absorbance meters, such as the ultraviolet (UV) detector used here, greatly underestimates the contribution of smaller particles (ca. <100 nm) due to the exceedingly small optical efficiency of particles within this size-refractive index domain.