What are syringe filters?
are important consumables for sample pre-treatment during HPLC and IC analysis in the laboratory. They are useful for filtering sample solutions, removing particulate contaminants, and protecting instruments. As a convenient and reliable filtration tool used routinely in laboratories, syringe filters facilitate the simplification of experimental operation steps and can significantly improve work efficiency. It is important to master the use of syringe filters and precautions.Syringe filters
are available in different membrane materials, and different materials are used in different applications. The membrane suitable for sample filtration should be selected according to experimental needs. The syringe filter must be attached to the syringe during use and gently tightened to ensure a good seal.
There are two types of syringe filters: sterilized syringe filters and non-sterile syringe filters. Sterilized syringe filters
need to be pretreated before use. After the filter installation is completed, the filter system is flushed with clean water and the filter operation can be performed after flushing. Before aspirating the sample, about 1 ml of air needs to be drawn into the syringe, which minimizes the liquid residue. The operation should be carried out in steps to ensure recovery efficiency. First, draw the sample into the syringe, invert the syringe and clear all residues at the tip; then, inject the sample syringe into the sample bottle after filtering; finally, remove the filter, draw the air into the syringe, reconnect the filter head, and push out all residual samples.
The syringe filter
is mainly used for the filtration of the active phase and samples in chromatographic analysis and has an outstanding effect on maintaining the chromatographic column and the infusion pump tubing system and the injection valve from being contaminated. It is widely used in fractional analysis, microanalysis, colloid separation, and sterile experiments. A needle filter is a single-use product, which can be used for liquid decontamination, gas vapor dehumidification, dust removal, and sterilization. It is used for sample pre-treatment of liquid chromatography, which can avoid the impurities of particles in the sample from blocking the column, maintain the pump pipeline system and the inlet valve from contamination, maintain the chromatographic system and extend the life.
Key points of liquid chromatograph operation filtration
Any particulate matter entering the HPLC system will be clogged by the sieve plate at the inlet end of the column. The subsequent result is clogging of the column, characterized by increased system pressure and distorted peaks, so various precautions should be taken, including operating procedures for the laboratory instrument itself and various filter designs to prevent or reduce the introduction of particulate matter into the HPLC system thereby extending the life of the instrument and column and improving the reliability of the data. In HPLC systems, there are three main sources of particulate matter: the mobile phase, the sample to be measured, and the wear and tear of the instrument system components.
Sample under test
Some laboratories filter all samples through a 0.45 um syringe filter before placing them in the autosampler tray (or manually), which is an effective way to remove particulate matter from the test sample. However, there is one more point of concern in this process. If syringe filters are used, it is impossible to obtain 100 samples passing through the filter and there will always be more or fewer losses. The losses come from several sources: adsorption of the filter membrane, adsorption of the particles filtered by the filter, leaks at the syringe filter membrane filter and syringe connection, etc. If there are losses, is the amount or concentration of the measured substance in the filtered liquid the same as in the original basic sample liquid? This topic usually requires experiments to confirm. The purpose of confirming this step is to increase the amount of work and usage.
A filter is a laboratory consumable device. The price of each filter varies from a few dollars to more than ten dollars. However, in food residue analysis, filtration has become an essential step due to the complexity of the matrix. In practical analytical work, each set of samples is usually tested with external standards, added recoveries, or quality control samples. Therefore, this step can be considered as a systematic error and ignored as long as the signal-to-noise ratio obtained during the test can meet the detection limit.
If all mobile phases consist of HPLC solvents, there is no need to filter the mobile phase. This is because of organic solvents of the HPLC grade, such as acetonitrile, methanol, etc. In the manufacturing process, they are filtered through 0.2m microporous filter membranes. Similarly, whether you purchase HPLC grade water or water prepared in a laboratory with an ultrapure water purification system, the latter step is also filtration through a 0.2m microporous membrane. However, if solids such as phosphate are added to any buffer, filtration of the mobile phase will be a necessary step. Although the buffer salt can be soluble and highly pure, it may still contain particulate matter. For example, when covering the plastic inner cap of a reagent bottle, plastic particles are produced when the plastic cap is pressed against the edge of the bottle opening In this case, the added solid can be completely dissolved, but a small number of impurity particles are present in the active phase as a residue.
Filtration of the mobile phase through a 0.45 um syringe filter is an effective way to remove all particles from the mobile phase It is also possible to use 0.22 um filters, but for this application, they are not more effective than 0.45 syringe filters and their filtration rate will be slower, especially if the quality of the reagents and water used in the laboratory is not very good. It is recommended that filtration is not required when using only HPLC grade liquids for mobile phase preparation, while all mobile phase components must be filtered before use.
It is also important to use a sink filter (two common materials are fused glass sand core filter plates and microporous metal) at the end of the delivery tube connecting the reservoir to the pump. This filter is sized for 10m microporous material, so it cannot replace the mobile phase filtration step, but it removes dust from the system and ensures the reliability of the reservoir bottle and infusion tube use.
Instrumentation system components
Another major source of particulate matter in worn HPLC systems is the wear of pump gaskets and injection valve rotation shafts. There are two different recommendations for the wear and replacement of infusion pump gaskets. The life span of a typical laboratory syringe filter is usually six months to one year, so it is recommended that these syringe filters be replaced for six months or one year. Laboratories should develop a regular preventive maintenance program based on the above view. The view is that it is cheaper to replace the infusion pump gaskets than to replace them with new columns because particles in the gaskets clog the columns. Some infusion pumps have glass grit cores or screens that filter out particles that wear off the pump gasket in the flow path to prevent these particles from flowing with the mobile phase to the column head. If such a device is available, refer to the infusion pump's operating manual and check to clean or replace the filter.
Another suggestion is that the original gasket seals well and is prone to mobile phase leakage after the replacement so as long as there is no leakage, the gasket should not be easily replaced.
Use of syringe filters
Follow these steps to use the syringe filter to achieve filtration.
a. Before aspirating the sample, aspirate about 1 mL of air into the syringe. This will make the liquid retention smaller.
b. Draw your sample into the syringe and then draw in 1 mL of air. Invert the syringe and wipe off any residue from the tip.
c. Use the connector to connect the syringe to the needle filter. Tighten gently to ensure a secure seal.
d. The solution in the syringe is filtered and injected into the sample bottle. Then, remove the filter, draw air into the syringe, attach the filter again, and press the pusher to filter out the residual sample. This allows for sample recovery.
Note: Use caution with syringes less than 10 mL in volume. This is because it is easy to generate enough pressure to burst the filter. Syringe filters are for laboratory use only, are disposable consumables, and are not recommended for reuse.
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