1、 Core function 1: Filter small impurities in the mobile phase/sample to avoid flow path blockage

Chromatographic analysis has high requirements for "mobile phase purity" and "sample cleanliness". Even tiny particles that are not visible to the naked eye (such as dust residue during mobile phase preparation, small insoluble substances in solvents, suspended solids, protein precipitation, and chromatographic column packing debris after sample pretreatment) may cause system blockage. The 4mm welded filter is the "first line of defense" to intercept these impurities:

Intercept particle size: The conventional 4mm welded filter has a membrane pore size of 0.22 μ m (for aqueous/organic mobile phases) or 0.45 μ m (for high viscosity or samples containing small amounts of coarse particles), which can effectively filter all solid particles larger than the membrane pore size;

Risk control of blockage: If impurities are not filtered, they will enter the chromatographic column with the mobile phase (the diameter of the packing particles in the column is usually 3-5 μ m, and even as small as 1.7 μ m in UPLC columns), causing blockage of the packing pores - at least causing a sudden increase in column pressure and unstable flow rate, and at most causing permanent damage to the chromatographic column (which cannot be recovered by flushing); At the same time, impurities may also block precision components such as injection valves and detector flow cells, leading to instrument malfunctions and shutdowns.

Adaptation scenario: The 4mm specification is suitable for the inner diameter of conventional chromatography systems (such as HPLC commonly used 1/16 inch tubing with an inner diameter of about 1.6mm, and the 4mm filter can be compatible and achieve efficient filtration). The welded design avoids the problem of leakage or impurity bypass caused by poor sealing of the "detachable filter".

2、 Core function 2: Stabilize the flow rate and pressure of the mobile phase to ensure analysis repeatability

The key data such as "retention time" and "peak area" in chromatographic analysis are highly sensitive to the "flow rate stability" of the mobile phase, while impurities or bubbles in the flow path can disrupt the uniformity of the flow rate. A 4mm welded filter can indirectly stabilize the flow path through "impurity interception" and "auxiliary degassing":

Eliminating flow rate fluctuations: The accumulation of impurities in the flow path can cause a local decrease in the inner diameter of the pipeline, resulting in a "pulse flow rate" (fluctuating pressure), which in turn causes the chromatographic peak shape to tail and the retention time to drift (such as components that originally peaked at 5.0 minutes may become 5.2 minutes or 4.8 minutes due to pressure fluctuations); After the filter intercepts impurities, the inner diameter of the flow path is uniform, the flow rate and system pressure are more stable, and the data repeatability (RSD) can be controlled within ≤ 2% (in line with chromatographic analysis requirements).

Auxiliary degassing residue: Some 4mm welded filter membranes have a certain degree of "breathability" (such as polytetrafluoroethylene PTFE membranes), which can filter impurities while releasing trace amounts of residual dissolved gases (such as oxygen and nitrogen) in the mobile phase. If the mobile phase contains gas, it will form "cavitation" at the pump head, causing unstable flow rate output and even damaging the infusion pump. The auxiliary degassing effect of the filter can reduce such problems.

3、 Core Function 3: Protect chromatography columns and precision components, reduce maintenance costs

Chromatographic columns are the most expensive and easily consumable core consumables in chromatographic analysis (a conventional HPLC column can cost thousands of yuan, while a UPLC column can cost tens of thousands of yuan). The 4mm welded filter directly protects the chromatographic column and other precision components through "pre filtration", extending their service life:

Protecting the chromatographic column: Impurities will adhere to the surface of the packing particles after entering the chromatographic column, not only blocking the pores, but also irreversibly adsorbing with the packing, resulting in a decrease in column efficiency (a decrease in the theoretical number of trays) and a decrease in separation (overlapping of adjacent peaks). After using a filter, the frequency of "backwash cleaning" of the chromatographic column can be reduced (when the filter is not in use, backwash is required after the column pressure increases, which will accelerate packing wear; after using a filter, the column pressure stabilizes and the number of backwash times decreases), extending the service life of the chromatographic column (usually from 300-500 injections to 800-1000 injections).

Protecting the injection valve and detector: The valve core and sealing ring of the injection valve are precision components, and the friction of impurities will accelerate their wear, resulting in inaccurate injection volume (affecting quantitative accuracy); If the flow cell of the detector (such as the UV detector flow cell with a volume of only a few microliters) is blocked by impurities, it will cause baseline drift, sensitivity decrease, and even require replacement of the flow cell (which is costly) - the filter can intercept impurities in advance to avoid damage to these components.