Particle Substrate for HPLC columns
Currently, three types of substrates are used as packing material for commercially available HPLC columns: silica gel, polymers, and organosilica. Each has the following characteristics and features.
Silica gel
Silica gel is the most widely used substrate for HPLC columns because of its low cost, high theoretical plate, and great mechanical strength. Silica gel with chemically modified alkyl chains such as C18 and C8 are commonly used as packing material of HPLC columns, although unmodified silica gel is also sometimes used. Because silica gel is usually dissolved by hydrolysis when an alkaline mobile phase is used, its usable pH range is narrower than that of other substrates (usually pH2-7.5). However, in recent years, various column manufacturers have used various technologies to develop silica gel with improved pH durability.
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Polymer
Polymers typically have a wider pH range than silica gel (pH 0-14) and are used as column substrates for analysis using acidic or basic mobile phases (e.g., ion exchange chromatography) and size exclusion chromatography. Depending on the type of gel used, there are various polymers such as hydrophilic and hydrophobic. Although the chemical durability such as pH is higher than other substrates, the number of theoretical plates and mechanical strength tend to be lower than those of silica gel and organosilica.
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Organosilica hybrid
Organosilica is a relatively new particle substrate compared to silica and polymers. The base material compensates for the low chemical durability of silica and the mechanical strength of polymers.
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The following table summarizes the features of these three types of substrates.
| Item/Base Material Name | Silica | Polymer | Organosilica |
|---|---|---|---|
| Mechanical Strength Impact on Pressure Resistance and Separation |
High | Low | High |
| Number of theoretical plates Impact on Separation |
High | Low | High |
| Silanol activity End capping has an impact |
Diverse | None | Diverse |
| Silanol activity End capping has an impact |
Diverse | None | Diverse |
| Generally Used pH Range Impact on the chemical durability of the column |
About 2-8 | 0-14 | About 1-12 |
