Packing procedures

It appears that the equation introduced by Van Deemter is still the simplest and the most reliable for use in general column design. Nevertheless, all the equations helped to further understand the processes that occur in the column. In particular, in addition to describing dispersion, the Kennedy and Knox equation can also be employed to assess the efficiency of the packing procedure used in the preparation of a chromatography column. 

The uncomplicated packing procedure of traditional media to yield efficient columns is demonstrated by the reduced plate heights of 2 or slightly below as reported for Sephadex and for the qualification of Sepharose columns for the determination of MWDs. 

Mount the upper adaptor, thereby compressing the gel bed, until the filter plate reaches the height of the column end piece. The lower adaptor should be adjusted before starting the packing procedure in order to reach 600 10 mm total bed height. 

The intraporous volumes and solid matrix volumes can be expressed as a percentage of the total bed volumes and should be equivalent to 50-55 and 15-18%, respectively. The solid matrix volume depends on the packing density and can be taken as a qualitative number for the control of the reproducibility of repeated packing procedures. 

One question of chief interest concerns the number of runs that can be run with one individual SEC column. The lifetime of the sorbent itself must be tested as well as the maximum run number for the packed column. Because column packing procedures for SEC columns are rather time-consuming and all SEC columns have to be checked very carefully with respect to performance, very frequent repacking of the column is unreasonable. Therefore, CIP protocols are generally necessary. The CIP protocol should be developed as part of the process validation program. 

PSS has developed proprietary packing procedures for its sorbents, that allow a homogeneous filling of the column hardware with no change in particle properties. This thoroughness in the packing procedure is reflected in the superior performance of PSS SEC columns and their long life, even in difficult conditions. 

Nicoud R. M. (1993) A Packing Procedure Suitable for High Flow Rate and High Stability Columns Using Cellulose Triacetate, LC-GC Int. 6 636-637. 

Unger, K.K. (editor)(1979). Silica columns packing procedure and performance characteristics. Porous Silica Journal of Chromatography Library, Volume 16. Elsevier, Amsterdam. pp.169 186. 

For example for the preparation of a 15 cm long, 4.6 mm i.d. stainless tube column, 2.5 g of octadecyl-bonded silica gel was suspended in 25 ml of hexanol-methanol mixture, and kept in an ultrasonic bath for a few minutes to remove air. After the reservoir was filled with the slurry, methanol was pumped in at 10 ml min -1 under constant pressure, 45 MPa (450 bar). After the replacement of slurry solvent by methanol, the flow was stopped and the pressure allowed to drop. When 0 MPa was reached the reservoir was removed. Then, 20 ml of water was added and methanol was again pumped in under the same conditions as before. Again, the flow was stopped and the pressure allowed to drop until it reached 0 MPa. The pre-column was removed and the analytical column closed. The maximum pressure that can be applied in the filling stage is based on the pore size, particle shape, and purity of the silica gel. This reproducible packing procedure is performed at constant temperature by using a water bath (60-BO °C). 

Ctriunm ovetloading, 52 Column packing procedure, 125, 145,146 apparatus, 146-148... 

Stainless steel tubes having i in. o.d. are most commonl employed. The tube wall must be thick enough to withstand presiMires up to 12,000 psi (816 atm) during the packing procedure. Most columns are prepared from tubes having 4.6 nun i.d. as such tubing is a standard commercial product and withstands these pressures. I... 

Bulk density, or packing density, includes all pores and voids (interparticle spaces) in its calculation. This value depends on the form of the particle (powder, tablets, or extmdates) and the packing procedure. It is extensively used in reactor designing since this value connects the solid volume with that of the reactor. 

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