Preparative Liquid Chromatography Columns

In previous chapters, liquid chromatography column theory has been developed to explain solute retention, band dispersion, column properties and optimum column design for columns that are to be used for purely analytical purposes. The theories considered so far, have assumed that solute concentrations approach (for all practical purposes) infinite dilution, and, as a consequence, all isotherms are linear. In the specific design of the optimum preparative column for a particular preparative separation, initially, the same assumptions will be made. 

In the first instance, the design of the optimum column for a given preparative separation will be considered.  

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Racemic mixtures of sulfoxides have often been separated completely or partially into the enantiomers. Various resolution techniques have been used, but the most important method has been via diastereomeric salt formation. Recently, resolution via complex formation between sulfoxides and homochiral compounds has been demonstrated and will likely prove of increasing importance as a method of separating enantiomers. Preparative liquid chromatography on chiral columns may also prove increasingly important it already is very useful on an analytical scale for the determination of enantiomeric purity. 

Golshan-Shirazi, S. and Guiochon, G., Theory of optimization of the experimental conditions of preparative liquid chromatography optimization of column efficiency, Anal. Chem., 61, 1368, 1989. 

Synthesis of compound A.A solution of 1,3-dibromopropane (10.1 g, 0.05 mol) in benzene (100 mL) was added to a solution of sodium telluride (NajTe 17.4 g, 0.1 mol) in ethanol (700 mL). After 3 h sodium borohydride (3.8 g, 0.1 mol) was further added to the mixture to produce sodium propane-1,3-ditellurolate, and then to the mixture was added a solution of the dibromopropane (10.1 g, 0.05 mol) in benzene (100 mL). The whole mixtnre was stirred at room temperature for 2 h. After usual work-up, the crude products were purified by silica gel column chromatography (eluent n-hexane/benzene) to afford compound A, which was further purified by preparative liquid chromatography. 

Figure 13 Purification of pravastatin sodium by preparative liquid chromatography. Reprinted from [12], copyright 2001, with permission from Elsevier. (Column 125 X 4.6 mm i.d. 3 pm Hypersil ODS mobile-phase gradient methanol water triethylamine acetic acid 45 54.8 0.1 0.1 for 13 min, to 99.8 0 0.1 0.1 over 9 min flow rate 1.2 ml/min detector UV 235 nm.)...

Figure 1.6 ICH Class 2 solvents measured using GC. Purification of pravastatin sodium by preparative liquid chromatography. Reprinted from [15], copyright 2004, with permission from Elsevier. (Column 30 m X 0.53 mm i.d. 3 pm OVI-G43 (Supelco) carrier gas helium at 5 ml/min injection in split mode total flow 25 ml/min injector temperature 140 C flame ionization detector temperature 25C C and oven temperature 40°C for 20 min, to 240°C at 10°C/min, maintain at 240 C for 20 min. The components are 1 methanol, 3 acetonitrile, 4 dichloromethane, 5 hexane, 6 cw-l,2-dichloroeth-ylene, 7 nitromethane, 8 chloroform, 9 cyclohexane, 13 1,2-dimethoxyethane, 15 1,1,2-trichloroethyl-ene, 16 methylcyclohexane, 17 1,4-dioxane, 18 pyridine, 19 toluene, 20 2-hexanone, 21 chlorobenzene, 22 ethylbenzene, 23 m-xylene, 24p-xylene, 25 o-xylene, and 26 tetralin. The solvents are dissolved in DMF and heated at 80X for 60 min, and a sample of the headspace is injected.)...

Kennedy, R. T. Jorgenson, J. W. 1989. Preparation and evaluation of packed capillary liquid chromatography columns with inner diameters from 20 to 50pm. Anal. Chem., 61,1128-1135. 

Pietrzyk, D.J. and Cahill, W.J., Amberlite XAD-4 as a stationary phase for preparative liquid chromatography in a radially compressed column, J. Liq. Chromatogr., 5, 781, 1982. 

Blom KF. Two-pump at-column-dilution configuration for preparative liquid chromatography-mass spectrometry. J. Comb. Chem. 2002 4 295-301. 

Koch DD, Polzin GL. Effect of sample preparation and liquid chromatography column choice on selec-... 

The hardware employed in preparative liquid chromatography typically has the capability for feedback control of the pumps, automatic column switching, column backflushing, recycling, gradient mixing, online pressure, flow rate, UV-absorbance, and temperature monitoring, and automatic pneumatic actuation of fraction collection valves based on time, volume, or UV-absorbance thresholds. These capabilities are afforded by computer control. 

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