Editing Column chromatography (section)

== Column preparation ==
A column is prepared by packing a solid adsorbent into a cylindrical glass or plastic tube. The size will depend on the amount of compound being isolated. The base of the tube contains a filter, either a cotton or glass wool plug, or glass frit to hold the solid phase in place. A solvent reservoir may be attached at the top of the column.

Two methods are generally used to prepare a column: the dry method and the wet method. For the dry method, the column is first filled with dry stationary phase powder, followed by the addition of mobile phase, which is flushed through the column until it is completely wet, and from this point is never allowed to run dry.<ref name="ShustermanMcDougal1997">{{cite journal|last1=Shusterman|first1=AJ|last2=McDougal|first2=PG|last3=Glasfeld|first3=A|year=1997|title=Dry-Column Flash Chromatography|journal=[[Journal of Chemical Education|J Chem Educ]]|volume=74|issue=10|pages=1222|bibcode=1997JChEd..74.1222S|doi=10.1021/ed074p1222|issn=0021-9584}}</ref> For the wet method, a [[slurry]] is prepared of the [[eluent]] with the stationary phase powder and then carefully poured into the column. The top of the silica should be flat, and the top of the silica can be protected by a layer of sand. Eluent is slowly passed through the column to advance the organic material.

The individual components are retained by the stationary phase differently and separate from each other while they are running at different speeds through the column with the eluent. At the end of the column they elute one at a time. During the entire chromatography process the eluent is collected in a series of [[fractionation|fraction]]s. Fractions can be collected automatically by means of fraction collectors. The productivity of chromatography can be increased by running several columns at a time. In this case multi stream collectors are used. The composition of the eluent flow can be monitored and each fraction is analyzed for dissolved compounds, e.g. by analytical chromatography, [[Ultraviolet–visible spectroscopy|UV absorption spectra]], or [[Fluorescence spectroscopy|fluorescence]]. Colored compounds (or fluorescent compounds with the aid of a UV lamp) can be seen through the glass wall as moving bands.