Fraction Collector
A fraction detector is a device that allows regular or specified samples to be taken from a column eluate and stored in a retrievable form. The storage vessels are usually small sample tubes or vials that are oriented in a rotating disk or in a moving belt, there movement usually being controlled by a microprocessor. On receiving a signal from the microprocessor, the next vial is placed under the column outlet and the eluate collected until receiving another signal from the computer. Once the properties of the chromatogram that describes the separation has been ascertained, then the collection program can be defined. The fractions can be collected on a basis of time either at regular intervals or a specific times to collect specific peaks. Alternatively the fractions can be collected by monitoring the detector output and when a peak starts to elute the fraction collector is activated and the peak collected in a specific vial. When the peak returns to base line the column eluate is then directed to waste until the next peak starts eluting. Fraction collectors are in common use with most liquid chromatographs. They are used to collect samples for further purification, subsequent exmination by spectroscopic techniques or for biological or organoleptic testing.
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Author: RPW Scott Book:Preparative Chromatography
Section:Preparative Packing-Preparative-Columns Axial-Compression
in figure 18. The apparatus consists of a column (capped at the top with a stainless steel frit) having a precisely controlled internal diameter and finish. The column contains a close fitting piston. The piston, which is mounted on a constant-pressure hydraulic jack, can be moved throughout the entire length of the column. It contains a porous frit at the top and a channel for passage for the mobile phase through its center. The channel is connected to the detector and thence to the fraction collector. To pack the column, the piston is withdrawn to bottom of the column and the column filled with the measured mass of packing. The amount of packing used will determine the effective length of the column. The hydraulic jack is activated and the packing compressed to the maximum pressure which is determined by the mechanical strength of the packing. If the packing is crushed by the use of too great a pressure, many fines will be produced, which cause the permeability to be
Preparative Packing-Preparative-Columns Axial-Compression
Author: RPW Scott Book:Preparative Chromatography
Section:Preparative Recycle-Development
The basic procedure is as follows. The two valves are set so that solvent from the reservoir is pumped through the injection valve to the column and the column outlet valve is set to the fraction collector. After the sample has been placed on the column, the column outlet valve is set to pass the column eluent back to the pump and the solvent selection valve set to the column eluent. Thus the mobile phase is continuously circulated through the column, through the detector, back to the pump and then back to the column. As a result the column is used over and over again many times, and each time the sample passes through the column, the resolution is improved. Unfortunately, the
Author: RPW Scott Book:Preparative Chromatography
Section:Preparative Radial-Flow
The core houses the inner frit, through which the eluent percolates and exits at the base of the column to a detector and hence to a fraction collector. The outer frit constitutes the column inlet, and consequently the sample has initially an extremely large area of stationary phase with which to interact. This renders the loading capacity of the radial flow column also very high. It is interesting to note, that as the solute progress radially through the stationary phase bed towards the center, the effective cross-sectional area of the column will become smaller. Consequently, the plate volume of the column will decrease (
Author: RPW Scott Book:Preparative Chromatography
Section:Preparative Radial-Flow
The method used for packing radial columns is depicted in figure 33. The packing is prepared in the form of a slurry and is pumped directly into the column between the two frits. The column exit to the detector and fraction collector is closed, and, as a result, the slurry solvent passes through the outer frit and exits via the normal mobile phase inlet port. The columns are very easily unpacked by adopting the reverse procedure. Figure 34. The Separation of Some Large Biomolecules Using Radial-Flow Reverse Phase Chromatography