APPLICATION OF 0.5-MU-M POROUS SILANIZED SILICA BEADS IN ELECTROCHROMATOGRAPHY

Nonporous organo-silica composites as beads with 0.5 mu m particle siz e were synthesized by means of a modified Stober process. The organic constituent was burnt off by subjecting the particles to calcination a t 550 degrees C, leaving particles with a highly interconnected inner particle porosity. The particles were silanized with n-octyldimethylch lorosilane after rehydroxylation. The n-octyl-bonded particles were sl urry packed into a fused-silica capillary of 85 mm length (380 mm tota l length) and 100 mu m inner diameter. An outlet and inlet frit were p repared by fusing the particles under hydrothermal conditions using a thermal wire stripper. The column was tested with thiourea in acetonit rile-Tris-HCl (80:20, v/v) at pH 8. An electroendosmotic flow (EOF) of 3 mm/s was generated at a voltage of 30 kV. The reduced plate height- reduced velocity curve showed a minimum value of h similar to 3.5-4 at an EOF of 2.5-3 mm/s. At a lower EOF, h increased linearly with decre asing EOF indicating that the plate height is diffusion controlled. Th e CE equipment (type 3DCE, Hewlett-Packard, Waldbronnm, Germany) was n ot optimized for minimum extra-column band broadening. The plate numbe r N varied between 212 800 (thiourea) and 83 600-288 800 for a test so lute of n-alkylbenzenes. The analysis time to separate a test mixture of five n-alkylbenzenes was less than 60 s. (C) 1997 Elsevier Science B.V.