Question

Discuss how silica gel column chromatography can be used to purify a mixture of compounds.

Answer 1

Soluton:

Column chromatography's versatility and convenience has made it one of the most widely used techniques for purifying compounds. Unlike recrystallization (another commonly used purification technique) compounds purified with column chromatography do not have to be solid. Column chromatography is also capable of isolating a number of compounds from a mixture. Another advantage of column chromatograph is that very little needs to be known about the compound's physical properties in order to use this purification method, making this technique very valuable when synthesizing or isolating novel compounds, in which little is known about the compound(s).

In column chromatography, the stationary phase is most often composed of silica gel particles of 40–63 μm. Different particle sizes are used for different kinds of column chromatography as the particle size is related to surface area. The differences in particle size dictate if the silica gel should be used for flash or gravity chromatography. In this application, due to silica gel's polarity, non-polar components tend to elute before more polar ones, hence the name normal phase chromatography. However, when hydrophobic groups (such as C₁₈ groups) are attached to the silica gel then polar components elute first and the method is referred to as reverse phase chromatography. Silica gel is also applied to aluminium, glass, or plastic sheets for thin layer chromatography.