Liquid purification or separation – With means to add treating material – Chromatography
Patent
1993-12-28
1995-01-03
Therkorn, Ernest G.
Liquid purification or separation
With means to add treating material
Chromatography
210656, B01D 1508
Patent
active
053783611
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a column for separation of substance mixtures, preferably on a preparative scale, with a liquid medium.
Liquid chromatography is used for separation of mixtures of substances. Thereby, such mixture is introduced in a column filled with an adsorptive agent, whereupon a liquid, referred to as an eluent, is allowed to flow through the column. Separation is achieved by the components of the mixture being retarded to a different degree by the adsorptive agent. Liquid chromatography is used for preparative *or analytical purposes. For analytical purposes, the substance mixture is introduced in the column in a liquid phase, whereupon an eluent is allowed to flow through the column and into a detector which records the amount of passing substance.
Preparative chromatography is carried out with the purpose of producing pure compounds, or isolating compounds from a mixture of substances. The amount of substance which is introduced into the column for such purpose is one to several powers of ten greater than what is introduced into a column for analytical purposes.
In preparative chromatography, in cases where the substance mixture is dissolved in a suitable liquid, the mixture may be introduced into the column via tubing connected to the end of the column. In other cases, the substance mixture is introduced in a solid phase. A standard procedure is to adsorb the mixture, in a separate operation, on an appropriate adsorbent material, which is thereafter introduced into the column on top of the adsorptive agent. The substance mixture may comprise synthetic products or natural products, e.g. plant extracts. Traditionally, long columns are used in this context, the top end of which is open. The column is packed with an adsorptive agent to a certain level, followed by the substance mixture. The uppermost part of the column is used as a reservoir for the eluent, which is allowed to pass through the adsorptive agent with the aid of gravity. This type of column allows for continuous supply of eluent. When higher flow rates are desired, than what can be achieved with a hydrostatic pressure alone, the eluent may be forced through the column by closing the top end of the column and applying gas pressure. The latter method, as currently applied, is referred to as "flash chromatography". Although this is an inexpensive solution, the method has drawbacks. Glass columns may explode by too high pressures applied, with the risk of glass splinter flying about, and further, the system has to be decompressed on filling or exchange of eluent. Decompression can cause formation of blisters whereby inhomogenities occur in the packing of the adsorptive agent.
Forcing of the eluent through the column with a pump bids great advantages. Supply of eluent and change of composition of the eluent can be done in a continuous manner on the suction side of the pump. With medium pressures, the compressibility of the liquid is negligible. Due to this, the risk of glass splinter flying about on breakage is small in use of columns which completely filled up with solid phase and liquid. Due to said fact, it is advantageous to supply the eluent to the column through a hollow piston, which can be brought into close contact with the adsorptive material, whereupon it is made to seal against the wall of the column.
This type of chromatography is sometimes referred to as medium pressure chromatography, which is carried out at a pressure up to a few tens of bar, e.g. 4 bar (0.4 MPa). Several manufacturers supply columns where requirements of sealing against the column walls are complied with. In many instances, columns are employed, designed as a cylinder of relatively thick glass (2-8 mm) wherein the length of the column may be made adjustable by means of a piston in the column. Usually the inlet or outlet of the column runs through the piston and piston shaft in flexible tubing which exits at the end of the piston shaft, alternatively a tube is provided having a connection for flexible tubing opening at the end thereof. Usually
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