Text Box: HIGH-EFFICIENCY LIQUID CHROMATOGRAPHY SEPARATIONS ACHIEVED BY MONOLITHIC SILICA COLUMNS KOSUKE MIYAMOTO1, TOHRU IKEGAMI1, TAKESHI HARA2, YASUSHI ISHIHAMA3, AND NOBUO TANAKA1, 4 1KYOTO INSTITUTE OF TECHNOLOGY, DEPARTMENT OF BIOMOLECULAR ENGINEERING, MATSUGASAKI, SAKYO-KU, KYOTO 606-8585, JAPAN; 2PHYSICAL CHEMISTRY INSTITUTE, JUSTUS LIEBIG UNIVERSITY GIESSEN, 58 HEINRICH BUFF RING, D-35392 GIESSEN, GERMANY; 3KYOTO UNIVERSITY, GRADUATE SCHOOL OF PHARMACEUTICAL SCIENCES, YOSHIDA, SAKYO-KU, KYOTO 606-8501, JAPAN; AND 4GL SCIENCES, 237-2 SAYAMAGAHARA, IRUMA 358-0032, JAPAN Introduction Ultrahigh column efficiency has been the focus of many chromatographers studying theories, columns, packing materials, or the separation of complex mixtures. Increasing the plate number (N) of a separation medium is the simplest way to increase separation capability, as resolution of two adjacent peaks (Rs) is proportional to √N. Such motivation could also be a driving force for a new technique and the advances of separation science. The possibility of generating a large number (e. g., 100,000–1,000,000) of theoretical plates has been studied since the beginning of high-performance liquid chromatography (HPLC), especially in liquid chromatography (LC) using particle-packed columns, where it is hard to achieve because of the relatively slow molecular diffusion of a solute in liquid phase. Guiochon recently discussed in detail the limit in performance of LC (Guiochon, 2006). Here we briefly review some studies that explore extremely high column efficiency. We also discuss possibilities of practical uses of monolithic silica columns capable of generating 100,000–1,000,000 theoretical plates. In LC, the efficiency (N, number of theoretical plates, equation 1) of a column (length L), is related to the plate height (H, equation 2), the particle size (dp) of packing materials, and the variance (σ2) of a Gaussian-shaped solute band acquired by the solute during its migration through a column. A reduced plate height (h) measures about 2 in a conventional system, which comprises pressure-driven operation of a packed column at optimum linear velocity. N can be calculated from a retention time of a solute (tR) and the base peak width (tW=4σ, σ is a standard deviation) for a symmetrical peak.

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