Particle size:

The effect of particle size of the adsorbent on the sharpness of chromatographic separations has been noted by many investigators. For sharp separations, it is recognized that a finely divided material is necessary. An adsorbent in the range from 100 to 200 mesh (149 to 74 µ) in particle size is specified. Some authors recommend the use of more finely divided materials. However, it is more difficult to pack columns uniformly if the adsorbent is very finely divided i.e., below 50 µ within particle size, and columns which are poorly packed provide rise to zones which are irregular in shape. A few adsorbents are available just as finely divided powders with particles below 10 µ in diameter, e.g. magnesium oxide. It is necessary to mix these adsorbents with filter aids such as Celite or Hyflo Super-Gel to obtain a practical rate of flow.