High resolution size determination of 20 nm colloidal gold particles by SedFFF

Purpose. Assessment of lower size limit of Sedimentation Field-Flow Fractionation (SedFFF), specifically to evaluate if the method is suitable to determine the size and size distribution of 20 nm colloidal gold particles with high resolution. Methods. Sedimentation Field-Flow Fractionation was used to determine the size of the colloidal particles. Due to the high density of gold it was possible to extend the lower size limit of SedFFF well below 20 nm. The size distribution of a gold colloid was obtained from the peak broadening caused by the polydispersity of the sample. The peak broadening due to instrumental imperfections was determined. For comparison purpose the particles were also sized using SEM and PCS. Results. The mean diameter of the particles was determined to be (20.87 +/- 0.05) nm, the standard deviation in size being 1.04 nm (about 5%). SEM could confirm that the particles are about 20 nm in diameter. A sizing with PCS was not possible. The particles have a strong tendency to aggregate and PCS yields a diameter that is much too large. Conclusions. At optimized analytical parameters Sedimentation Field-Flow Fractionation is an effective method to measure the size of gold particles as small as 15 nm with an accuracy of about 0.1 nm. The polydispersity of the sample can easily be determined.