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Impurities can not only get into the system from outside but also from the system itself. The main sources are mainly the piston seals the pump or the rotor seal the injection valve, which can produce abrasion with increasing operating time. This abrasion can lead to deposits / blockage on the stationary phase or in the HPLC system.
In addition to regular maintenance of the system it is recommended to use an inline filter to protect the column and the plant. But what is the inline filter and why makes its use a lot of sense? And what is important in choosing the right inline filter?
The in-line filter can be positioned at various locations of the HPLC system. If the inline filter is installed between the pump and the injector, particles and impurities are removed from the eluent. Likewise, abrasion of the piston seal is intercepted, so that the rotor seal of the injection valve is protected from abrasion and fine particles. When positioning directly in front of the column after the injection valve and contaminants from the sample are removed and abrasion of the rotor seals.
In addition to the inline filter it is usually recommended to use a guard column. Molecules that can be attached irreversibly to the main column can not be retained with the inline filter. Inline filters are available in various designs. In addition to housing, which is either made of PEEK or stainless steel can also choose between different fittings. These depend on the place where the inline filter should be installed. Thus, there are also housing, which are provided for the direct connection to the analytical column.
The frits for the inline filters are usually made of stainless steel and are often surrounded by a ring of PEEK. This serves as a seal ring, while minimizing the dead volume of the inline filter, so that no negative effects such as peak broadening can be expected. Stainless steel frits can be used for the current analysis. For applications requiring high corrosion resistance and biocompatibility, frits made of other materials such as Titanium or polymers are available. Also, the surrounding ring can be made of other materials, such as of PTFE. The user then has the possibility to choose a matching inline filter depending on the sample to be analyzed and the chemical properties of the mobile phase.
Typical pore sizes of the frits are 2 and 0.5 microns. When using columns with a particle size of <5 micron, frits with 0.5 microns should be used. For UHPLC systems and columns with particle sizes below 2 microns using frits with a pore size of 0.2 microns is recommended. The maximum pressure is 1000 bar and they have a low dead volume.
In the long term, the use of inline filters in the HPLC analysis has many advantages and saves money. Maintenance costs will be reduced and the facility and the separation column with usage of the inline filter will guarantee an extended service life.