A liquid chromatographic procedure for assessing silica gel adsorbents is described and the results obtained from the examination of 10 commercial materials representing the range of adsorbents available are given. All comparative tests have been carried out under isocratic conditions, and under such conditions it is shown that the micro particulate packings produce the highest efficiency and thus the highest resolution and peak capacity, together with the shortest analysis times, providing the sample to be separated contains solutes of similar polarity and is close to that of the mobile phase. Although possessing relatively poor resolving power and peak capacity, the pedicular packing provides short analysis times for simple mixtures of relatively wide polarity range. As many liquid chromatography separations are routine and repetitive in nature it is highly desirable, from a point of view of both simplicity and economy, to operate such analyses under isocratic conditions of development. If unmodified silica gel is employed, where chromatographic activity is directly related to surface area, it is suggested that a series of four micro particulate adsorbents having surface areas of approximately 15, 75, 150 and 350 square meters per gram, respectively, would produce a comprehensive family of adsorbents. From such a family, appropriate packing could be selected to permit wherever possible routine separations to be achieved under isocratic conditions, even when the solutes of interest in the mixture cover a significant polarity range.
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Scott et al. (1974) studied this question.