请各位高手帮忙翻译一段有机方面的外文,万分感谢!!!? In order to obtain satisfactory results,the tube must be uniformly packed with the adsorbent; uneven distribution may lead to the formation of cracks and channels and to considerable distortion of adsorption band shapes. If there is any doubt concerning the uniformity of particle size of the adsorbent powder it should be sifted before use to remove the larger particles; fines are removed from the adsorbent using a sedimentation procedure immediately prior to column packing. In this the alumina or silica gel adsorbent is stirred into between five to ten times its volume of the selected solvent or solvent system, allowed to settle for five minutes and the supernatant liquor decanted off; the procedure is repeated until the supernatant liquid is clear. As a rough guide the amount of adsorbent used should normally be 25-50 times the weight of the material to be separated. A slurry of the adsorbent in the solvent (approximately l : 10) is poured through a funnel into a clean dry column clamped vertically, in a position away from draughts or warm air currents from a radiator or electric oven, etc. The adsorbent will settle evenly and free of air bubbles if assisted by gentle tapping of the tube with a wooden rod. Forpacking large columns the slurry is best contained in a separatory funnel and stirred with a link-type stirrer while it is allowed to flow into the column. Solvent is removed via the tap fitted to the adapter at the column end and more slurry is added until the required length of column is obtained. Some workers recommend that a second column is fitted to the top of the first so that all the slurry can be added in one portion thereby yielding a more perfectly uniform column of adsorbent on settling. Fresh solvent is allowed to flow through the column under the hydrostatic pressure that is envisaged for subsequent chromatographic development, until no further settling is apparent. At no time during the column preparation nor in subsequent use should the level of liquid fall below the level of adsorbent. [ ]查看更多2个回答 . 5人已关注