Preparative Liquid Chromatography Prep LC

Sample clean-up can be done rapidly using a short LC column operated under gravity flow or under vacuum, centrifuge or syringe pressure. The most popular phases include silica and bonded phases. Disposable and inexpensive columns are available and can be found under the following trade names Sample Enrichment and Purification, PreSep Extraction, Bond-Elute, and solid-phase extraction. For example, purification of sulfamethazine in milk by SPE followed by quantitative analysis by TLC has been described earher 

Low pressure LC is very similar to the experiment performed by Tswett. A variety of stationary phases can be used and relatively large particle sizes are needed to keep the pressure drop low and facilitate packing. The ideal mobile phase should be inexpensive and volatile to facilitate sample recovery. The eluent is collected in separate tubes using an automated fraction collector. Since the samples often contain a lot of impurities, the column is very likely to be contaminated. Cleaning can be achieved by rinsing with solvents or 

Flash chromatography is a quick preparation technique that is, in effect, a hybrid between medium pressure and short column chromatography. It uses a short, fat column (e.g., 1-5 cm i.d. x 45 cm) packed with silica gel and filled with solvent. Compressed air is used to compress and remove the air from the solvent which then elutes quickly. The sample is then added and the column filled again. Pressure is adjusted to achieve a separation in 5-10 minutes. It is a fast and inexpensive method for the preparative separation of mixtures requiring only moderate resolution. Use of 40-63 pm sihca gel and a pressure driven flow rate of 2.0 in/min are essential for successful separation [30]. 

High Performance Prep LC is another variation of prep LC and is discussed in more detail in Chapter 2. 

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