A new separation technique takes advantage of sub-2-µm porous particles.
HPLC
remains the workhorse technique in liquidphase separations. The method has two fundamental roots. One is gel-permeation chromatography for the characterization of polymers (1); the other is GC. HPLC began to emerge when GC researchers turned their attention to liquid-phase separations (2, 3). The original LC columns were typically 50–100 cm long, with a 1–2 mm i.d., and packed with 50–200-µm-diam particles. Shorter diffusion distances were known to provide better performance. However, it was not possible to prepare high-performance columns with particles with diame-
Jeffrey R. Mazzeo • Uwe D. Neue • Marianna Kele • Robert S. Plumb Waters Corp.
ters 30 kV (30). time, or 5 higher productivity (resolution per unit time). The benefit of 1.7-µm particles over 3.5-µm ones is 1.4 The same principle could be applied to HPLC. Columns with a diameter narrower than the standard column diameter of HPLC higher resolution in half of the time, or 3 higher productivity. could be operated at much higher pressures because the friction- More efficient peaks translate to narrower and taller peaks. Peak width is inversely proportional to the square root of efficiency; al heat could be dissipated (31–33). If instruments with extended pressure range were available the peak height is inversely proportional to peak width. Thereand smaller particles could be used, then a higher separation per- fore, when smaller particles are used to make the peaks narrowformance or a faster analysis could be achieved, compared with er, the peak height is also increased. If the detector is assumed to classical HPLC. The term ultra-high-pressure LC was intro- be concentration-sensitive (as is the case for UV detectors) and duced to define the use of sub-2-µm particles packed into very the detector noise remains constant, then sensitivity, as defined long (>150-mm) capillary columns (
