In order to keep HPLC and UHPLC systems free of contaminants which can damage the analytical column or even the entire system, great care is taken with all solutions that come into direct contact with the system. It is advisable to use high-purity solvents for the production of mobile phases and to filter them. The sample to be analysed must be filtered e.g. with a syringe filter before the injection into a chromatography system.
Impurities may enter the system from outside and may also come from the system itself – primarily through degradation of piston seals of the pump or the rotor seal of the injection valve, which causes abrasion during prolonged use. This abrasion can lead to deposits and clogging in the HPLC system.
In addition to regular maintenance of the system, the use of an inline filter is recommended to protect the column and the system. What are inline filters and what difference do they make? What considerations are there when selecting the right inline filter?
Inline filters are made of PEEK or stainless steel with a frit inside and standard fittings on both ends. Inline filters are available in different formats: replaceable frits only or inline filters which can be completely replaced.
The inline filter can be positioned at various points in the HPLC system. If the inline filter is installed between the pump and the injector, particles and impurities are removed from the eluent. There will be no abrasion of the piston seal and the rotor seal of the injection valve is also protected from abrasion and fine particles.
When positioned directly in front of the separation column after the injection valve, impurities in the eluent and particles released through abrasion of the rotor seal are also separated from the sample.
In addition to the inline filter, the use of a guard column is also recommended to prevent impurities from reaching the analytical column. Irreversibly retained compounds cannot be trapped with the inline filter.
Inline filters are available in different versions. Filter housing can be made of PEEK or stainless steel. In addition, there is a choice of different fittings, depending on where the inline filter is to be installed. There are also housings that are intended for direct connection to the analytical column.
Inline filter for direct connection to the HPLC column with replaceable frit
Disposable inline filter for direct connection to the HPLC column
The frits of the inline filters are usually made of stainless steel surrounded with a PEEK polymer ring for enhanced sealing. This also minimises the dead volume of the inline filter to prevent negative effects such as peak broadening. Stainless steel frits can be used for common analysis methods. For applications that require high corrosion resistance or biocompatibility, frits made of other materials such as Titanium or polymers are available. This enables the user to select the appropriate inline filter depending on the sample to be analysed and the chemical properties of the mobile phase.
Typical pore sizes of the frits are 2 µm and 0.5 µm. When using separation columns with a particle size
In the long run, the use of inline filters in HPLC analysis saves money as maintenance costs and time are reduced and can greatly extend column life.