The HPLC separation technique is widespread in pharmaceutical and chemical industries where its accuracy, precision and selectivity are important to the research, development, production and quality control of many commercial products. During the 1970s, spherical silica particles rapidly displaced first generation granular particles for analytical applications because they were much easier to prepare into stable columns. The first spherical silicas designed for HPLC appeared commercially as thin porous layers on solid silica cores, but their applications were limited due to very low surface area, phase coverage and retention factors.
Totally porous, spherical silica dominated the HPLC market from the 1980s to the 2000s with average particle size continually decreasing from 10µm to 5µm to 3µm.1,2 The trend towards smaller particles is driven by improved performance in terms of speed, sensitivity, and resolution. Smaller particles, however, require higher operating pressures, and in 2004 instruments were commercialised that could utilise columns prepared with sub-2µm particles. Figure 1 illustrates the chromatographic performance of four typical particle sizes used in HPLC. It is clear from Figure 1 that smaller particles lead to greater efficiency, resolving power and sensitivity.
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