The column of choice for analytical methods development is very easy; the best column for an application is simply the column that gives the highest performance under the most favorable condition desired by the end-user. Most analytes are acidic, basic or neutral. The best initial approach is to use a mid-range pH, such as pH 7. The standard SMT OD C18 and O C8 columns are the best choice for use at this pH because they provide superior column lifetime, extremely high selectivity and resolution. Acetonitrile or methanol and water are normally the first choice for mobile phase. Another option is combination of organic solvent with phosphate buffer (with buffer range pH 6.2-8.2) or acetate buffer (with buffer range pH 3.8-5.8). Method development optimization can continue from here by changing several factors, including mobile phase, pH, column temperature (up to 95Â°C). SMT OD C18 is uniquely stable at high temperatures, a characteristic that can be used as an additional tool to improve resolution of thermally stable compounds or analytes.
When chromatographic separation is done in a normal phase mode, the surface chemistry of the stationary phase has a polar characteristic. The mobile phase is generally nonpolar organic solvent (such as hexane or heptane). Because of the limited flexibility in variation of the mobile phase polarity and functional stationary phase, separation in normal phase mode has not grown as much as reversed-phase mode. However, continuous advancement in surface modification has rejuvenated interest in normal phase chromatography. Furthermore, there are some separations that are achieved more conveniently using normal mode. Silica, alumina, polymers, and a few other metal oxides are the most commonly used substrates for normal phase separation. The important features include high surface area, availability in high purity, and homogeneous functional groups. Generally, SMT normal phase columns consist of silica as the substrate. SMT also offers a series of specialty packing materials for various applications including alumina and magnesia-silica.
In this mode of chromatography, the separation depends upon the exchange of ions between the mobile phase and the ionic sites of the packing (cationic or anionic). The stationary phase matrix has a functional group with a fixed ionic charge covalently attached to it . An exchangeable counter ion from the mobile phase buffer preserves charge neutrality. The mobile phase usually contains a large number of counter ions opposite in charge to the surface ionic group. Separation Methods Technologies, Inc. has developed new series of ion-exchange packing materials with its novel SAM technology. These packings are offered for all stages of separation science from analytical scale levels to process scale purification levels. Analytical columns are usually available in 5 and 10 micron particle sizes. Bulk packings are offered in larger particle sizes like 20, 40, and 60 microns. These packing are not only suitable for low pressure column chromatography but also perfect for solid phase extractions.
SMTgelâ„¢ (silica-based) columns are specialty SMT columns designed for specific applications including gel permeation (GPC), ion exchange, reversed phase, hydrophobic interaction, hydrophilic interaction, and affinity chromatography. SMTgelâ„¢ columns are packed with chemically modified silica particles with functional molecules for specific applications and pore sizes to accommodate wide range of analyte molecular weights. The packing materials feature modified surface chemistry designed to minimize sample adsorption on the silica substrate. All popular biomolecule separation modes are covered by SMTgelâ„¢ (silica-based) columns. Because SMTgelâ„¢ columns are silica-based, they must be operated within the recommended pH range of 2.0-9.0. Detailed operating conditions are described in the information accompanying the columns. We recommend protecting these columns with the appropriate SMTgelâ„¢ guard column.