Separation of gold nanoparticles with a monolithic silica capillary column in liquid chromatography.

A separation system for gold nanoparticles was developed using monolithic silica capillary columns with 50 µm i.d., which were prepared via in-situ sol-gel processes. Gold nanoparticles with five different average sizes were synthesized via reduction of tetrachloroauric acid (HAuCl(4)) under different synthesis conditions, and were evaluated by UV-visible spectrophotometry, dynamic light scattering as well as transmission electron microscopy before they were separated using the developed system. The results showed that all of the gold nanoparticles had a certain size distribution, and the mean sizes obtained were 13, 17, 33, 43 and 61 nm, with σ = 2.5, 2.7, 5.2, 5.1 and 5.6 nm, respectively. Transmission electron microscopy showed that the samples with mean sizes of 13 and 17 nm were almost spherical, while larger samples were slightly non-uniform. The agglomeration of gold nanoparticles as the sample could be prevented by using a sodium dodecyl sulfate aqueous solution as the mobile phase, and gold nanoparticles were retained by adsorption on the silica surface. Separation with 8 mM sodium dodecyl sulfate as the eluent and a 1000-mm column was successful, and the separation of gold nanoparticles with 61 and 17 nm or 61 and 13 nm was demonstrated. The separation results obtained using a nonporous silica packed column as well as monolithic silica columns with or without mesopore growth were compared. It was found that separation using the mesopore-less monolithic column achieved better resolution. Through the use of a 2000-mm separation column, the mixtures of 61, 43, 17 nm and 61, 33, 13 nm could be separated.