New Directions in High-Throughput and High-Resolution HPLC
by Ronald E. Majors
In analytical HPLC column technology, there are a number of approaches for developing faster or higher efficiency separations. Most recently the increased use of sub-2-um particles packed into short columns has generated faster separations without sacrificing resolution of the longer columns packed with larger 5-um particles. Longer, high-resolution columns packed with these tiny particles do generate greater pressure. Compared to 5-um columns, columns packed with 2- to 3-um particles provide higher throughput but the efficiency is not as good and the pressure drop is not as high as the sub-2-um columns. The recently re-discovered, superficially porous particles for large and small molecules provide lower pressure drop than the sub-2-um and offer shorter diffusion path lengths and better efficiency than the 2- to 3-um particles. Silica- and polymer-based monoliths represent another approach for increased speed but flow rates were higher than required for satisfactory MS detection but the recently introduced 2.0-mm internal diameter silica-based monoliths may change that. The lower pressure drop of monoliths allows multiple columns to be connected in series for increased plate counts. Instrumentation such as detectors, data systems and mass spectrometers may be challenged to keep up with rapidly eluting peaks coming from high speed columns. High temperature can be used as a variable to further improve throughput, modify selectivity and provide lower pressure drop. This presentation will discuss the pros and cons of each approach and make some recommendations for optimal use of columns of each type. A future projection in column advances concludes the presentation. |
