Related Parameters and Performance of the Filter Membrane

The importance of filtration in chromatographic pretreatment

Due to the precision of the chromatographic system and the requirements for the accuracy of the result analysis, the filtration of samples is particularly important. Filtration can protect the chromatographic system and the chromatographic column, extend the service life of the column, and improve the degree of data.

Filtering can eliminate pressure fluctuations caused by particles generated by friction and baseline fluctuations caused by irregular impurities and can eliminate the interference of the detection system due to the presence of bubbles. Therefore, a filter membrane disc is usually used to filter the mobile phase.

Select filter membranes of different types and pore sizes to filter the mobile phase and samples to clarify and eliminate bacteria and remove impurity particles. It is of great significance to protect the chromatographic system and the chromatographic column. So we should know the related parameters of the filter membrane.

Related parameters of the filter membrane

1. Pore size: pore size rating refers to distinguishing the pore size by intercepting 100% challenge bacteria of a certain size under very strict test conditions. The specified conditions must include the size and concentration of the organism (or molecule) to be tested, the pressure to be tested and the method to be tested.
2. Air flux: it is a method for measuring air passing through the filter. That is the flow rate through which air flows at different pressures, different porosity, and different filter areas.
3. Bubble point: in the microporous membrane industry, a specific liquid is used to soak the membrane, and at a certain temperature, it is called the minimum pressure that must be squeezed out of the membrane pores.
4. Filter efficiency: under its specific pressure, the filter defines its filtering efficiency by the total amount of filtration and the size of obstructive particles. In general, the lower the obstruction, the lower the pressure, and the higher the efficiency of the filter.
5. Filter material life: the longest use time of the filter under certain operating conditions. Many factors will affect it, for instance, the filter material, nature, and its operating temperature.
6. Hydrophilicity: hydrophilic filter membranes usually have a special chemical layer so that the filter membrane can be wetted by water; hydrophilicity is a reference to the repulsion of water.

Hydrophobic membranes absorb little or no water at all. In observation, it can be seen that the small water droplets stay on the surface of the filter membrane without being adsorbed by the surface and spreading into the water surface. The degree of hydrophobicity depends on the pore size of the filter material and the characteristics of the filter material.
7.Flow rate and flow volume: the flow rate is the total amount of the filtrate passing through the filter membrane per unit of time at a specific temperature and pressure. The flow volume is closely related to the surface properties of the filter membrane.

Flow rate and flow volumes are two important parameters of filter material and design performance. This performance depends on the following aspects:
1) Viscosity: viscosity determines the ease of liquid flow. Under certain temperature and pressure conditions, the higher liquid viscosity, the lower flow rate, and the higher pressure needed to achieve the same flow rate.
2) Pressure difference: the pressure difference between the inlet and the outlet of the filter.  The filter pressure difference will increase if the filter is loaded fully.
3) Porosity: it refers to the ratio of the volume of all pores on the membrane to the volume of the membrane. As a rule, the pore area of the filtration membrane is 50-90%, and the flow rate has a direct relation with the membrane porosity.