A Simple Method for Purifying Silica Gel for Column Chromatography Chemical producm are often purified by column chromatography'-2. Silica gel is the mmt r c m m m adsorhent for this purpose but ir very expensive and also not suitable for multiple chrumatoflaphg reparatima. ( h e r a l l y , several pounds uf silica gel is accumulated during lab experiments from undergraduate courses. However, this used silica gel is impure, and the procedures available for its purification are long and too tedious for chemistry students. The procedure using sodium hypochlorite solution (&lo%) is quick and efficient and requires only one laboratory period.
Experimental Add 300-500 g of dry silica gel (to be purified) t o a 1-L beaker containing 500 mL distilled water. Heat the contents of the beaker t o bailing with a hot plate (open flame can be also used). Add, dropwise, 40-60 mL of aqueous sodium hv~ochloritet o the mixture and k e e ~the heatiue for 1 h. Caution: Check The n H of the NaOCl solution durine the addition. If i t is basic it mav dissolve the silica eel. Allow the mixture to cool t o room temoerature. and decant the liouid.
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sodium chloride. Let the silica gel to dry in a dust-free place, and activate i t in an oven a t 100 "C for 1 h before use. The yield ranged between 75-85s. A mixture of azo-dye standards was chromatographycally separated using both brand-new silica gel and the adsorbent purified by this method. The adsorptive capacity of the purified silica was thus tested and proved by the student t o he adecluate. We have conducted this laboratorv activitv for the vast . vear . and consider the educational result extremelv gratifying for teacher and students. Heftman, E., Ed. Chromatography; Reinhold: New York, 1961. Srivastava, V. K.; Srivastwa, K. K. Introduction of Chromatography; Chand: New Delhi, 1985. Miller, J. M.,Ed. SeporationMethods in Chemical Analysis; Wiley-Interscience: New York, 1975. 'Author to whom correspondence should be addressed. Anionlo E. Guarconl and Vfctor F. Ferreira4 Universidade Federal Fluminanse 24.000-Nit& Rio dB Janeiro. Brazil
Volume 6 5
Number 1 0
October 1988
89 1
