TOPICS IN LIQUID CHROMATOGRAPHY Part 2. Optimum Bed Density [OBD™] Columns: Enabling Technology for Laboratory-Scale Isolation and Purification Dramatic improvement in stability, lifetime, efficiency, peak shape, and reproducibility results from continuing investigation of, and innovation in, the design of particles, columns, and packing processes.

DRUG DISCOV ERY CHALL ENGES P REPA RAT IV E LC For modern pharmaceutical research laboratories to fill new drug pipelines with viable candidates, thousands of synthetic and natural compounds must be isolated, identified, synthesized, purified, characterized, screened, and tested. Tools and techniques that optimize and streamline these processes shorten development cycles, increase competitive advantage, and, ultimately, save lives. Laboratory-scale chromatographic isolation and purification plays a central, and rapidly expanding, role in these efforts. Purifying the contents of huge combinatorial...

a movable piston.8 A slurry of 10-µm particles was poured into the vertically-mounted column. Once the inlet cap was secured, the piston was moved upward from the bottom to effect the packing. In contrast to radial compression, this scheme was later described in its commercial embodiment as axial compression. Figure 1. These hitherto unpublished 1975 Waters R&D prototype photos show how thin-plastic-walled, 5.7 x 30 cm PrepPak® cartridges, the initial embodiment of the invention of radial compression,5 could easily be dissected, making directly visible what never had been seen before: the actual...

As manufacturers gained confidence in creating good analytical LC columns, they generally applied the same 5-10 µm-particle packing methods to prep LC columns up to 50 mm I.D. T hese were intended for high-throughput pharmaceutical applications. However, as stated earlier, frustration with short unpredictable column lifetimes has led to a search for a way to produce consistently superior prep LC columns. 0.700 Optimum Packed-Bed Density Dynamic compression techniques are not without drawbacks. Too much pressure may fracture particles, creating less homogeneous, denser, lower-permeability beds....

High-Pressure Slurry Packing Localized Bed Expansion Near Inlet Axial-Ram Slurry Packing Localized Compression Near Inlet OBD Process Optimum Bed Density Throughout Efficiency [plates] Figure 4. Optimized bed density in an OBD column is achieved by judicious application of a tuned amount of axial force only at the column inlet. Traditional Prep LC Column* Waters is a primary producer and supplier of over 30 different silicaand hybrid-particle packings. Over three decades of experience with the interplay of particle properties, column design, and packing technique enable the achievement of optimal...

C. Effective Maintenance of Efficiency and Resolution An accelerated lifetime test was devised to punish small particle prep LC columns with cycles of solvent viscosity changes. As can be seen in Figure 6, the bed stability and performance of the new OBD columns is outstanding. A similar longer-term test [Figure 7] demonstrates little variation in reduced plate height and USP peak tailing factor over a 7–8 week period. Note that a reduced plate height value near 2 indicates a high-quality well-packed column. Once a baseline separation is achieved, the real challenge in a high-throughput environment...

D. Scale-Up with Confidence As described above, preparative OBD columns ensure performance equivalent to that of analytical columns. This simplifies scalingup a separation from analytical to prep LC. An example is shown in Figure 11. Nimodipine was separated from its impurities on a SunFire C18 analytical column. A total load of 6 mg on the analytical column permitted baseline resolution between peaks for impurity 2 and its parent compound. The scale-up factor is simply the ratio of the cross-sectional area of the larger- to that of the smaller-I.D. column; 17 x 6 mg = 102 mg. Clearly, these...

References: NOTE: Where indicated below, use bold search term following * to access PDF document in Waters Library at . 1. A.J.P. Martin and R.L.M. Synge, Biochem. J. 35: 1358–1368 [1941] 2. P.D. McDonald, James Waters and His Liquid Chromatography People: A Personal Perspective, Waters Whitepaper *WA62008: 20 pp [2006] 3. P.D. McDonald and B.A. Bidlingmeyer, Strategies for Successful Preparative Liquid Chromatography, Chap. 1 in: J. Chromatogr. Lib. 38: 1–103 [1987], see esp. pp. 82–88 and references therein 4. U.D. Neue, HPLC Columns: Theory, Technology, and Practice, New York: Wiley-VCH [1997]...