Material Harvest® Reverse Phase Silica Gel

Silica gel is used in organic chemistry for the purification and isolation of synthetic compounds (i.e. post-reaction “harvesting” of chemical products).

Our reverse phase silica gel is manufactured in accordance to the highest specifications. As shown in Figure 1, the synthetic process entails grafting octadecyl moieties on the surface of regular silica gel, followed by end-capping of the residual OH groups.

Figure 1 – Surface functionalisation of regular silica gel, followed by end-capping

By end-capping the residual OH groups, C18 reverse phase silica gel is insoluble in polar solvents including methanol.

Reverse Phase Column Chromatography

There are many different types of reverse phases that can be used for research and development. The most common of these are based on Silica Gel 60, having a particle size distribution of 230 – 400 (i.e. 40 – 63 µm). The number "60" in "Silica Gel 60" means that the pore diameter of the silica particles is 60 Å.

In terms of the loading or carbon content, 17% is one of the most common configuration for reverse phases. Reverse phases having "high" carbon content (23%) or "low" carbon content (11%) are also available, but these may be more useful in situations where compounds move too quickly or too slowly, respectively, across the C18 silica gel.

We offer academic discounts to universities and consumption-based discounts to industrial laboratories - please do not hesitate to contact us for more detail.

Lecture Notes on Reverse Phase Column Chromatography

Column chromatography is a purification technique used in organic chemistry and synthesis. It can potentially isolate a desired compound from a mixture of unwanted substances – for example the product of a chemical reaction may be separated from its crude mixture by use of column chromatography.

Column chromatography utilizes a stationary phase, otherwise known as a sorbent or an adsorbent, which is normally packed in a glass column. Common examples of stationary phases include silica gel and alumina. The mixture of compounds is applied at the top of the column and a solvent or solvent mixture, known as the “eluent” or “mobile phase”, is allowed to flow through the silica gel or alumina.

In reverse phase column chromatography, the stationary phase is functionalised with an alkyl substituent such as octadecyl – an alkyl chain having 18 carbon atoms. This type of silica is commonly referred to as C18 silica gel; it is the most common reverse phase available in the market. Other reverse phases include C12, C8, C4, C1, C-cyclohexyl and C-phenyl.

Polar compounds elute faster than their non-polar counterparts when reverse phases are employed. This is the opposite situation in respect to chromatography with unmodified or "regular" silica gel, therefore the technique is traditionally referred to as being "reverse".

The degree of hydrophobicity decreases as the carbon chain length also decreases: in other words, C18 has the highest degree of hydrophobicity and C1 has the lowest degree of hydrophobicity. As a result of this principle, shorter chain lengths like C1 and C4 are better where less retention towards non-polar compounds is needed. In other words, if your compounds “stick” on the C18 silica very strongly, an alternative reverse phase such as C4 may be more useful.

If you would like to receive more information please email techsupport@materialharvest.com