Purification Applications
From LEAP
| Purification Applications |
| Application Type | |
| STANDARD AND SPECIAL | |
| Application ID | |
| Description | |
| Purification Applications |
General Description
The purpose of preparative-scale liquid chromatography is the isolation of materials conforming to a specified purity in the amounts that depend on the intended use of the product. Possible uses include the isolation of materials for structural elucidation, for biological or sensory evaluation (Eg:DMPKA), for organic synthesis or commercial applications. The scale of the operation includes laboratory, pilot plant and process-scale system. Process-scale separations will not be treated specifically in this section, since they represent a specialized area of chemical manufacturing and economic forecasting that the analytical chemist is infrequently exposed to.
From its inception liquid chromatography has been used as a preparative technique. Most chemist are familiar with the gravity feed glass column systems containing coarse adsorbent packings that are the main stay of laboratory practice. These low cost and easy to prepare and operate columns have many virtues. Not among them, however, are high resolution, short separation times and easy automation. When any of these factors are considered crucial then more sophisticated systems are required based on smaller particle sorbents with a narrow particle size distribution, that in turn are operated at above atmospheric pressure in the optimum mobile phase velocity range. These goals are best achieved using medium pressure and high pressure liquid chromatography.
Instead of gravity, a slight gas overpressure can be used to increase th sample throughput. This method is often called flash chromatography. Flash chromatography, also known as medium pressure chromatography, was popularized several years ago by Clark Still of Columbia University, as an alternative to slow and often inefficient gravity-fed chromatography. Flash chromatography provide a rapid (“over in a flash”)inexpensive general method for the preparative-scale separation of mixtures requiring only moderate resolution in amounts of 0.01 to 10 g depending on the difficulty of the separation and the column diameter (typically, 1-5cm).
When selecting the appropriate preparative-scale liquid chromatographic method for conditions requiring higher resolution or shorter processing times it is necessary to consider the intended use of the purified material. For example, 1-10 mg of a pure sample suffice for spectrocopic identification, while 1-10 g might be the minimum amount of an intermediate useful for an organice synthesis. The amount of sample required dictates the size of the column and the operating conditions necessary for the separation. The simplest approach to increasing the amount of sample recovered is to scale up an analytical separation using the same column packing, column length and linear mobile phase velocity while increasing the column diameter. The analytical separation should be optimized to maximize the separation factor between critical peak pairs at the expense of a longer separation time to permit the use of higher column loadings before the bands overlap. If the sample loading does not exceed the linear region of the sorption isotherm the results obtained are easily extrapolated from the analytical separation. Whith most analytical instruments the largest column size that can be used is about 25 cm long and 2.5cm internal diameter containing approximately 65 g of silica-based packing and requiring an optimun flow rate of 10-15 ml/min. For larger columns special purpose preparative scale instruments are usually neede to provide adequate flow and pressure capacity. also
The technique is difficult to perform manually due to the demands for precise timing and reproducing exactly the same experimental conditions. Automation solves both of these challenges. LEAP has developed a robotic solution to the sample Prep and introduction to the LCMS. It consists of a Twin PAL workstation configured as shown below. There are two cooled zones on the workstation: A cooled stack at 1oC for the samples and labeled reactants and a cooled chromatography module which contains the injection valve, the column selection valves and the columns themselves. These are maintained also at around 1degree C. The automation process is controlled using LEAP Shell software.
Significant Markets
- Pharmaceutical - Drug Discovery,
