Preparation And Evaluation Of Gold Microspheres And Submicron Silica Particles As Stationary Phases In μHPLC And PCEC

Column, which was called the heart of the HPLC, is the most important part in liquid chromatography. The most popular columns nowadays were packed by silica microspheres; however, the limited pH range (pH 2-8) that silica column can tolerate and its irreversible adsorption to alkaline compounds limited the usage of the silica column in some certain fields. Also, there is very high pressure when using small microspheres as column packing materials, which makes it difficult to use submicron size particles in HPLC. In this work, the efforts were made to develop new type of packing materials such as spherical gold particles and submicron silica particles.1. The monodispersed gold microspheres were made by reducing tetrachloroauric (III) acid using iso-ascorbic acid as reduced reagent. The gold microspheres were modified with n-octadecanethiol; and then the physical properties of the particles were characterized, respectively, by Scanning electron microscopy (SEM) and FT-IR spectrometry. The SEM image showed the particle size was about 3.5 um and FT-IR result demonstrated that n-octadecanethiol was bonded to the surface of gold microspheres. The surfaces area and the average pore diameter were 49.4 m2/g and 4.8 nm,respectively. 2. A 19 cm section of a total length of 36 cm capillary with 100μm I.D. was packed electrokinetically using C18 modified gold microspheres. The column was evaluated inμHPLC and pCEC. The mobile phase of extreme pH (80% methanol, pH 1 and pH 12) was used to flush the column for 140 hours, in order to investigate the chemical stability of the column by comparing the retention factor before and after flushing. There was no remarkable deterioration after flushing, which demonstrated the column was stable under strong acidic and basic condition. Five neutral compounds uracil, benzene, naphthalene, 2-methylnaphthalene and acenaphthene were separated usingμHPLC to examine the retention behavior of the column, and over 50000 theoretical plates per meter and acceptable symmetry were obtained. The separation of acidic and basic compounds was also investigated along with the effect of pH on separation of basic compounds. Because the gold microspheres were negatively charged, the separation of acidic compounds was better than that of basic compounds and the increase of pH can inhibit the adsorption of basic compounds to obtain better separation. Three alkaloid, namely, caffeine, theophyline and lobeline were separated using mobile phase of high pH, and over 50000 theoretical plates per meter and acceptable symmetry were obtained. Repeatability of C18-Au packed column was investigated through the run-to-run and day-to-day repeatability of retention time and peak height. The RSDs were lower than 2.6% and 4.1%, respectively. The electrochromatographic properties of the column were investigated using a test mixture of aniline and benzoic acid, and efficient separation of them was obtained when a positive or a negative voltage above 5 kV was applied.3. Submicron monodisperse silica spheres were prepared by means of hydrolysis of TEOS and subsequent condensation of silicic acid in alcoholic solutions. The effect of concentration of TEOS, ammonia and water on particle size and dispersivity was investigated. The particle size increase when the concentration of TEOS was below 0.3 M, the adhesion became severe when above 0.3 M. Ammonia was necessary to form particles,and increase of ammonia can enlarge the particle size. In a certain range, higher water content can increase the size of the particles. However, too much water makes the particles smaller or even stops the reaction. The 400,500and 600 nm particles were prepared by the means of adding TEOS at a time; the 700and 800 nm particles were prepared by the means of adding TEOS and water two or more times. As the adding times increased, the adhesion increased, too. The 800 nm particles were dried, calcined and then packed in a 100 micron i.d. capillary. This capillary was tested and efficiency of 50000 theoretical plates per meter was obtained and there was strong EOF when voltage was applied on the column.In summary, gold microspheres as chromatographic stationary phase for the first time were prepared, modified characterized and packed in a capillary column. The packed column was evaluated in bothμHPLC and pCEC. Compared with the silica column, the C18-Au column can be stable under extreme acidic and basic conditions. The monodisperse submicron size particles were prepared and were tested as packing material. Preliminary results demonstrated the potential usage of these particles in pCEC.