Optimisation of on-channel preconcentration in flow field-flow fractionation for the determination of size distributions of low molecular weight colloidal material in natural waters

Flow FFF with UV detection has been used to determine the size distributions of colloidal material in natural waters. The method has been optimised with respect to flow rates, buffer composition and membrane type. The use of an on-channel preconcentration (focusing) technique allows very low colloid concentrations to be fractionated. The preconcentration process gives close to quantitative recovery with a detection limit equivalent to 9 μmol l−1 DOC for a 1.74 ml sample.