Welchrom® C18 are unend-capped packing mateirals of C18 adsorbent. The more residual silicohydroxyl on the surface provides additional polar interaction, which makes the hydrophobic bonded silica gel more closely in contact with the more polar extractant, and enhances the retention ability of alkaline compounds and polar substances. Welchrom® C18 is a general-purpose stationary phase for extraction of polar and non-polar compounds, compared to end-capped Welchrom® C18E. The carbon load of Welchrom® C18 was about 17%. The average particle size of silica gel in packing materials was 45μm, the average pore diameter was 60Å, the pore volume was 0.80cm3/g , and surface area was 480m2/g