Chromatography solvent gradients

In column chromatography, solvent gradients can be formed stepwise by... 

Supercritical fluid chromatography pressure gradient solvent delivery system Pierce Chemicals Life Science Laboratories Ltd Sedgewick Road Luton... 

The effect on chromatography is to complicate the separation greatly. If we consider a reverse-phase separation, the first thing we notice is an almost irreversible binding of protein to the column. Even after protein removal, we find polar peaks, which overload the early part of the chromatogram and tail into the compounds of interest. The components that are more nonpolar than our compounds of interest adhere to the column and must be washed off before the next injection. To ensure polar elution before our target compounds and nonpolar removal afterwards, we are almost forced to run solvent gradients. 

One standard method approach that appears to have wide application in the pharmaceutical industry is the use of reversed-phase high performance liquid chromatography (HPLC) with a wide solvent gradient program. For example, a linear gradient from 95%... 

Methyl-4-nitroanisole (29.1 mmol) dissolved in 46 ml apiece glacial acetic acid and acetic anhydride at 0°C was treated dropwise with 6.9 ml 18 M sulfuric acid and Cr03 (80.8 mmol) portionwise over 60 minutes. The mixture was stirred an additional 15 minutes, then poured over ice, and a precipitate isolated. The solid was washed with cool water, then purified by flash chromatography with a solvent gradient of 15-50% EtOAc/hexanes, and the product isolated in 24% yield as a white solid. 

The most important techniques of the chromatography principle are column elution based on a solvent — non solvent gradient, and column elution with a superimposed temperature gradient. 

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