Packing Materials

The best column technology is useless without the proper packing material. There are two main aspects to consider when selecting the packing material: chemical and physical. The chemical aspect is related to the chemistry of the purification problem and is not discussed here since it is very much product dependent. A material well suited for a given application may be inadequate for another. The physical aspects, however, can be discussed in general terms. The various models of HPPLC have shown that there is an optimum value of the ratio dp/L for any separation problem (dp is the particle size and L the column length). In typical conditions, for columns operated at a pressure of 30 to 60 bar, an 'optimum' particle size is about 10-20 |im with a column length between 20 and 50 cm. Accordingly, rather small particles have to be used for PLC.

It is also very important to keep the particle size distribution as narrow as possible, since small particles in the distribution have a very strong effect on the column permeability and large particles strongly influence the column efficiency. In other words, a material with a large size distribution tends to produce low-efficiency columns with low permeability. It is usually considered that the ratio dp10/dp90 should be less than 1.5 for a good material (dp10 and dp90 being the particle sizes corresponding to 10% and 90% of the cumulated volume-based size distribution).

Besides the average particle size and the size distribution, other physical properties of the packing material are important, particularly the specific surface area and the pore size. It is desirable to maximize the surface area of the material in order to increase its adsorption capacity. Increasing the surface area, however, usually means decreasing the pore size and thus the access of the molecules to the internal pores of the particles. There exists an optimum pore size and specific surface for each compound to be purified.

Among the other important physical parameters, one should also mention the mechanical strength of the particles, since they must resist the stress of the compression technique used.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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