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Instrument and Column Technology
The drive for increased chromatographic performance has led column manufacturers to continuously develop smaller and smaller particle sizes for liquid chromatography. Column efficiency is inversely proportional to the particle size, hence reducing the particle size increases the number of theoretical plates. Although smaller particles provide higher efficiencies, the trade-off is an increase in the operational back pressure. The introduction of commercially available high pressure capable instrumentation paved the way for the routine use of sub-2 micron particles. These small particles were shown to provide exceptional performance, particularly at flow rates higher than typically used with larger particle sizes, as demonstrated by their respective van Deemter plots (Figure 1, also see AKN0010: Band broadening and the van Deemter Equation). As shown, the optimum flow rate for 1.7 μm particles is greater than that of 3 and 5 μm particles. Additionally, 1.7 μm particles exhibit a flatter curve, meaning that a Figure 1: Van Deemter plots for various particle sizes. The minimum of each curve represents the optimal flow rate (i.e. highest efficiency) for that particle size. they can still deliver high performance at higher flow rates. In contrast, larger particles show a sharper drop-off in performance when the flow rate is elevated beyond the optimum value.
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