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Inline Filters
Inline Filters are excellent protection for sensitive system components. Placed between the pump and sample injection valve, inline filters trap particles released through degradation of the piston seal. Without an inline filter, particles can be flushed through the system's tubing to the sample injection valve, resulting in valve damage and further system contamination. These filters are pressure rated to 6,000 psi (414 bar) and use a 2 μm or 20 μm stainless steel frit. An 8° distribution cone helps spread the flow of the mobile phase over the entire surface of the frit, while the 0.050” (1.3 mm) diameter thru-hole allows virtually unrestricted solvent flow rates.
Use of inline filters
Inline filters have a housing made of PEEK (polyether ether ketone) or stainless steel with a frit inside and standard fittings at both ends. There are inline filters that can be completely replaced if necessary, or a version where only the frit needs to be 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. Abrasion of the piston seal is also intercepted so that the rotor seal of the injection valve is protected from abrasion and fine particles. When positioned directly in front of the column after the injection valve, impurities and abrasion from the rotor seal are also separated from the sample.
In addition to the inline filter, the use of a pre-column is usually recommended. Molecules that are irreversibly attached to the main column cannot be retained with the inline filter. Inline filters are available in various designs. In addition to the housing, which can be made of PEEK or stainless steel, there is also a choice of different fittings. These depend on the location where the inline filter is to be installed. There are also housings that are designed for direct connection to the analytical column. The frits of the inline filters are usually made of stainless steel and are often surrounded by a ring made of PEEK, for example. This serves as a sealing ring and at the same time minimizes the dead volume of the inline filter so that no negative effects such as peak broadening are to be expected. 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 also available. The surrounding ring can also be made of other materials, such as PTFE. This enables the user to select the appropriate inline filter depending on the sample to be analyzed and the chemical properties of the mobile phase. Typical pore sizes of the frits are 2μm and 0.5μm. When using separation columns with a particle size of <5μm, a frit with 0.5μm should be used. For UHPLC systems and columns with particle sizes below 2μm, the use of frits with a pore size of 0.2μm is recommended. Their maximum pressure is 1000 bar, and they have a low dead volume. In the long term, the use of inline filters in HPLC analysis offers many advantages and saves money. Maintenance costs are reduced, and the system and its separation column will repay you for using the inline filter with an extended service life.
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