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Introduction
There is an increasing demand for high throughput analysis and columns capable of ultra fast run times. A requirement for increased column efficiency has led to the development of smaller particle size materials.
Previously, the particle size was effectively restricted by the pressure limitations of commercially available HPLC pumps. The introduction of ultra high pressure pumps has enabled the use of smaller particle sizes to become more practical. However, many smaller particle columns have now been specifically designed so that they may still be used on conventional HPLC equipment, eliminating the need for new instrumentation.
Features of Sub 3µm Silica Particles
Resolution Equation
Resolution (Rs) = 1/4 N (power 0.5) (α- 1) (k/(k+1))
As the resolution equation shows, as particle size decreases the resolution will increase proportionately to the square root of efficiency. Table 1 also illustrates that as particle size is reduced then column pressure is seen to increase far more rapidly than resolution (eg. when reducing the particle size from 5µm to 2µm, the performance will more than double, which results in a resolution increase of nearly 50%, but pressure can be expected to increase by a factor of 5). However, this pressure increase is as predicted, since the pressure obtained is inversely proportional to the square of the particle size.
Instrumentation Requirements
Generally, sub 3µm columns are available in short column lengths and small column i.d.s, leading to low column volume. Consequently, to maximise performance, the dead volume of the HPLC system has to be carefully considered and optimised irrespective of whether or not the columns are being operated at ultra high pressures. In addition, fast data recording is usually required to ensure that the chromatographic performance is accurately recorded.
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