1973 Volume 22 Issue 7 Pages 832-836
In a previous paper, we reported the preparation of a new type of precoated plate for thin-layer chromatography which was made by heating a mixture of Kieselguhr and glass powder at a temperature under 750°C for several minutes. Although thermal expansion coefficients of Kieselguhr and glass powder are very much different from each other, the welding of these two substances readily took place. It seemed interesting to us that Kieselguhr, even when heated at such a high temperature, did not lose its chromatographic activity.
In general, sintering of Kieselguhr is known to begin at 600°C to 700°C as in the case of silica gel. The heating period in our experiments was so short that sintering of Kieselguhr did not seem to take place. There is no information in the literature about the effect of heat on Kieselguhr for thin-layer chromatography at such a high temperature. Therefore, heat treatment of Kieselguhr was studied under various conditions, i. e., at 450°C to 750°C for 2 to 7 minutes. Using the Kieselguhr thus treated, thin-layer chromatographic separation of test mixtures such as polychlorinated biphenyls (decachlorinated biphenyl and Kanechlor 600) and azo dyes (Sudan Red G, Sudan Yellow, Butter Yellow and p-methoxyazobenzene) was performed. Table I shows no change in physical properties of the heated Kieselguhr, and Table IIV indicate the constancy of Rf; values and the good separation of the test mixtures. These results confirm that sintering of Kieselguhr does not occur under the condition described above.
We have clarified the welding mechanism of the Kieselguhr sintered plate by means of scanning electron microscopic method (the micrographs were taken by using JEOL Model JSM-2 scanning electron microscope). It is evident from photograph 5 that Kieselguhr is fixed among the three dimensional matrix formed by the sintered glass powder and glass plate without loss of its surface structure. Thus sintered glass powder plays a role of binder between Kieselguhr and glass plate.
