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Editors' Series: UHPLC: Where We Might Go
Ultrahigh-pressure liquid chromatography (UHPLC) columns today are 5 to 15 cm long, packed with sub-2-micron particles, and operated with upper pressure limits of 15,000 to 18,000 psi. In comparison to HPLC, current UHPLC instrumentation has emphasized separation speed over separation efficiency. Analysis times are often 3 to 5 times faster in UHPLC, while separation efficiencies are generally comparable to or somewhat higher than HPLC.
Future UHPLC systems may begin to incorporate capability for operation at still higher pressures, moving toward pressures of 50,000 psi. Higher pressures will enable the use of still smaller particle packing materials (1.0 to 1.5 micron particles) for still faster analysis times, as well as longer columns (50 to 100 cm) with higher separation efficiencies (100,000 to 250,000 theoretical plates). As higher pressures are used, greater attention will need to be paid to the issue of heat generation and dissipation associated with pumping mobile phase through beds of extremely fine particles. Column bores will need to be sub-millimeter, and ultimately of capillary dimensions (50 to 300 micron i.d.) in order to provide the necessary efficient heat dissipation. Such columns are an excellent match for electrospray mass spectrometry as the detector. Columns packed with superficially porous particles and monolithic columns will likely be integrated into this development, in the form of 1-micron superficially porous particles, and monoliths with through pores of a few hundred nanometers. Operation of columns at higher temperatures will also be increasingly utilized as a means to increase speed of analysis. In this regard, capillary columns greatly simplify the use of high temperature LC, due to their very rapid heat transfer of characteristics. Sponsored by: Waters Corporation
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