Detection of nanocolloids with flow-field flow fractionation and laser-induced breakdown detection

A new nanosize colloid detection method comprised of flow-field flow fractionation (FFFF) with laser-induced breakdown detection (LIBD) is presented, which is capable of characterizing the colloid size distribution as well as determining the number density of each size fraction in very low concentrations. The method facilitates the detection of aquatic colloids particularly in the lower range of nanometer size (< 50 nm) with the sensitivity much higher than a laser light-scattering method (LLS), i.e., the lower ppb range. The method is tested with a mixture of polystyrene colloids in three different nominal sizes, 19, 50, and 102 nm, and the results are compared with those of the LLS method. For colloids of 19-nm diameter, the present method demonstrates the detection sensitivity over 3 orders of magnitude better than that of the LLS method. The limitation of the detection sensitivity arises from the surface bleeding of a ceramic frit overlying the separation channel of the used FFFF instrument.