Development of high-resolution determination methods for nanoparticles

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Hydrodynamic chromatography (HDC) conditions have been examined for the separation of silica colloids with 5-78 nm diameters. Conventional HPLC columns with 25 cm×4.6 mm I.D. were prepared and employed for HDC.Interstitial spaces among packing materials are usually employed in HDC. Considering the size of silica colloids, non-porous silica gel with 2-5 μm was packed for the HDC separation of silica colloids. Eluents for HDC of silica colloids were examined in detail, and phosphate buffer solutions with pH larger than 7 gave reasonable elution volumes for silica colloids. A 10 mM phosphate buffer with pH 7.1 was the optimum eluent for silica colloids. The separation column with smaller particle diameter provided better resolution for silica colloids. The silica colloids were detected with a UV detector based on turbidimetry, and the larger colloid gave larger signal intensity.The elution volume of silica colloids slightly increased with decreasing flow rate. It was speculated that lower … More flow rate enhanced the diffusion of analytes into narrower channels.It is required to use smaller particles or to use a longer column in order to improve the resolution. However, higher pressure drop over such separation columns are indispensable, and preparation of such columns is not easy. Since monolithic silica columns having higher permeability and better resolution will overcome these drawbacks, hydrodynamic capillary chromatography (HDCC) was examined for the separation of colloidal particles.Monolithic silica capillary columns with 50-200 μm were prepared and examined for the HDCC separation of colloidal silica and gold nanoparticles with 13-61 nm particle diameters. It was found that smaller elution volumes were observed for larger nanoparticles. In order to minimize the extra-column dispersion, the injection volume was reduced to 20 nL or less, and the on-column detection was carried out. It was expected that the monolithic silica capillary columns possessed mesopore with 10-15 nm and size-exclusion effect could be involved for the elution of smaller nanoparticles. Furthermore, eluents were examined in detail so as not to cause adsorption and coagulation of nanoparticles while passing through the separation column and connecting tubes. It was found that phosphate buffers with pH 7 were good for silica colloids, while aqueous sodium dodecylsulfate solutions were good for gold colloids. Monolithic silica capillary columns with 50 cm in length provided resolution comparable to 25-cm packed columns. It was expected that longer monolithic silica capillary columns would achieve better resolution. Less