Emptying the Column

After this is done, open valve (9) on the tubing. Empty the column by using a pump or by gravity. One should limit the flow to 1-2 ml/min. Fractions of 2-5 ml are suitable in most cases. However, observe that a volume of 0.5 ml is the volume that separates two zones which can be seen to lie 1 mm apart in the column. If one desires to keep such zones separate one must reduce the size of the fractions. Since the handling of such small fraction volumes is difficult, it is recommended that where the zones have to be more clearly separated, a narrower pH range be used for electrofocusing. 

It is important to measure the pH of the fractions at the same temperature which prevailed during electrofocusing. Basic fractions must be 

There are several difficulties in using a flow cell to measure the pH. Continuous measurements are affected by the electrodes in the electro-focusing column and by the electrolyte in the system. Special precautions are necessary to eliminate disturbances from the surroundings. It is recommended that the pH of each fraction be measured individually by a combined glass column electrode unless the user can take all these precautions and calibrate the equipment for a continuous measurement of pH. 

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Empty the column carefully into the hood sink. 

V, can be obtained by emptying the column and refilling it with water to the level marked in step 5-24. The volume of the water is then determined by draining the column into a graduated cylinder. If the column is to be reused this procedure may be performed before gel is added to the column and the bed allowed to form to the mark. In this particular experiment V, was 41 ml. 

Flush the empty column with the slurry solvent prior to use to ensure that the column, column frits, and plumbing are clean and wetted. Empty the column before introducing the slurry suspension. 

When a steady state has been obtained, empty the column by using a fraction collector. The fractions containing the sample of interest are then selected and pooled. These fractions wall also contain carrier ampholytes of the narrowest pH range suitable for the sample in question. 

Glass, 61 cm (2 ft) X 3 mm I.D. packed with 3% OV-1 on Gas-Chrom Q, 100-120 mesh is used. To precondition the column before packing, fill the empty column with a 50% soln. of dimethyl-dichlorosilane in hexane and allow to stand for 5 min. Empty the column and wash with 50 ml of hexane followed by 50 ml of chloroform. Dry the column with a stream of dry air. Pack the column to within 8-9 mm of each end, and fill the remaining portions of the column with a small piece of silylated glass wool Temperature... 

The simplest form of extractor is a spray column. The column is empty one liquid forms a continuous phase and the other liquid flows up, or down, the column in the form of droplets. Mass transfer takes places to, or from, the droplets to the continuous phase. The efficiency of a spray tower will be low, particularly with large diameter columns, due to back mixing. The efficiency of the basic, empty, spray column can be improved by installing plates or packing. 

Another very important design consideration is that between the point at which the sample is introduced and the point at which it is detected, the dead volume in the equipment must be kept to a minimum. Dead volume means any empty space or unoccupied volume. The presence of too much dead volume can lead to disastrous losses in efficiency (Fig. 2.3c and 5.3b show examples of this). Clearly there will be some dead volume in the column itself, which will be the space that is not occupied by the particles of stationary phase. 

This is usually caused by changes in the carrier gas flow rate or column temperature. Flow rate changes can be caused by leaks in the system upstream from the column inlet, such as in the injection port (e.g., the septum) by low pressure in the system due to an empty or nearly empty carrier supply or by faulty hardware,... 

First, an empty analytical column, a pre-column, and a slurry reservoir are connected in series. The narrow-bore analytical column and pre-column are... 

The concept of column void volume (Vg) is important for several reasons. Void volume is the volume of the empty column minus the volume occupied by the solid packing materials. It is the liquid holdup volume of the column that each analyte must elute from. Note that the void volume is equal to the void time multiplied by the flow rate (T). 

Enzyme thermistors can be altered for measuring the activity of soluble enzymes. For this purpose, an inactive or empty Teflon column can be used as a reaction chamber. The sample and a buffer containing a suitable substrate in excess are passed through heat exchangers and thoroughly... 

The interparticulate volume ( (,) is equivalent to the dead volume of the column and is defined by the retention volume of the largest PS standard. The corresponding porosity (e, ) can be calculated by dividing by the volume of the empty column. 

An important measure concerning column characterization in LC is the column permeability, which represents the capacity of the support to transport the mobile phase as consequence of a pressure drop occurring over the column. In other words, the permeability of a column determines the required pressure to achieve the desired flow rate. The linear flow velocity (u) across an empty cylindrical column is given by... 

Equation 10.45 assumes that the column was initially empty of solute and equilibrated with a stream of solution. A similar equation can be used if FA is carried out in the staircase mode. 

FIGURE 16.3 Dependences of the polymer retention volume on the logarithm of its molar mass M or hydrodynamic volume log M [T ] (Section 16.2.2). (a) Idealized dependence with a long linear part in absence of enthalpic interactions. Vq is the interstitial volume in the column packed with porous particles, is the total volume of liquid in the column and is the excluded molar mass, (b) log M vs. dependences for the polymer HPLC systems, in which the enthalpic interaction between macromolecules and column packing exceed entropic (exclusion) effects (1-3). Fully retained polymer molar masses are marked with an empty circle. For comparison, the ideal SEC dependence (Figure 16.3a) is shown (4). (c) log M vs. dependences for the polymer HPLC systems, in which the enthalpic interactions are present but the exclusion effects dominate (1), or in which the full (2) or partial (3,4) compensation of enthalpy and entropy appears. For comparison, the ideal SEC dependence (Figure 16.3a) is shown (5). (d) log M vs. dependences for the polymer HPLC systems, in which the enthalpic interactions affect the exclusion based courses. This leads to the enthalpy assisted SEC behavior especially in the vicinity of For comparison, the ideal SEC dependence (Eigure 16.3a) is shown (4). 

Figure 1 A matrix representation of two possible coupling schemes in the WiGLEformalism. The rows correspond to n, the index of a particular realization of the ensemble, and the columns correspond to the index of the other realization of the ensemble which may or may not be in the set Sw,n, depending on whether the matrix element is fill or empty, respectively. The matrix on the left (a) corresponds to the banded coupling case, in which a given particle is coupled to the nearest w particles (for a specified ordering) through the friction. The matrix on the right (b) corresponds to the block-diagonal case, in which a given particle is always coupled to a prespecified set of w particles.

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