Medium pressure chromatography packings

The term medium-pressure liquid chromatography (MPLC) covers a wide range of column diameters, different granulometry packing materials, different pressures, and a number of... 

The submitters purified the product by medium pressure liquid chromatography on a 60-cm x 5-cm column packed with 230-400 mesh silica gel 60 purchased from E. Merck. Ethyl acetate was used as eluant at a flow rate of 4 0 mL per min. Fractions (20 mL) were collected and analyzed by thin layer cHromatography. 

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]. 

Another approach to preparative liquid chromatography is to use medium pressure system (upto 300 psi, max), with shatter-proof glass columns and Merck silica gel 60 (230-400 mesh). These column can be dry packed with 100 g silica gel and will separate 5 g of solute in 2-3 hours. Solvent used does not need to be of analytical grade so long as it is distilled. 

Another means of resolution is to use a chiral material in a physical separation. Currently, many resolutions are done using medium- or high-pressure chromatography with chiral column-packing materials. Resolution by chromatography depends upon differential adsorption of the enantiomers by the chiral stationary phase. Differential adsorption occurs because of the different fit of the two enantiomers to the chiral adsorbent. Figure 2.7 shows such a separation. Topic 2.1 provides additional detail on several types of chiral stationary phases. 

The newer LC techniques of flash column chromatography and short path or medium pressure column chromatography though offering resolution approaching that of thin layer are still comparatively slow and expensive in terms of packing and solvents. The principal advantage of these techniques is in their preparative capability. 

Figure 11.3. General procedure for dry packing medium-pressure, preparative-scale, liquid chromatography columns. (From ref. [6] Academic Press).

Packings for medium- and high-pressure liquid chromatography... 

The method (27) describes the measurement of clonidine in human plasma and urine by combined gas chromatography-mass spectrometry with ammonia chemical ionization. Addition of [ 84] clonidine to plasma or urine is followed by ethylacetate extraction of clonidine from alkaline medium, back extraction into acid extraction into ethyl ether from alkaline medium and evaporation of the extract to dryness. Trimethylanilinium hydroxide is added to the residue, and dimethyl derivatives of clonidine are formed by on column methylation with an injection-port temperature of 250 for g.c. -70-eV m.s., the glass column (1.8 m X 2 mm) packed with 3% of OV-17 on Gas-Chrom Q (100 to 120 mesh) is operated at 245 . With He s carrier gas (15 ml min" ) NH3 is admitted to an ion-source pressure of 0.2 Torr, and ions are monitored at m/e 258 and 264. Graphs of peak height ratios (m/e 258 to 264) vs amounts of clonidine in urine (up to 40 ng ml-i) and in plasma (up to 5 ng ml i) are rectilinear. The precision for assay of clonidine in plasma is 11% at 0.25 ng ml" and 5% at 0.5 ng ml" and the lower limit of determination is 0.1 ng ml. ... 

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