Any particles in the liquid chromatograph analysis system will be blocked by the screen at the inlet end of the column. The final result is that the column is clogged, which is characterized by an increase in system pressure and deformation of the chromatographic peak . Therefore, various precautions, including operational procedures and various filtration designs of the commodity instrument itself, are required to prevent or reduce the entry of particulate matter into the HPLC system, thereby extending the life of the instrument and the column and increasing the reliability of the data. In HPLC systems, there are three main sources of particulate matter: the mobile phase, the sample being tested, and the wear of the instrument system components.

1 , mobile phase

If the mobile phase consists of a high performance liquid chromatography grade solvent, the mobile phase does not have to be filtered. This is because high performance liquid chromatography grade organic solvents, such as acetonitrile, methanol, etc., have been filtered through a 0.2 μm microporous membrane during the manufacturing process. Similarly, whether you are buying HPLC grade water or water used in an ultrapure water purification system in the laboratory, the final step is through a 0.2 μm microporous membrane. However, if any kind of buffer is added to a solid such as phosphate, mobile phase filtration will be a necessary step. Although the buffer salt may be soluble and highly pure, it may contain particulate matter. For example, when the plastic inner lid of the reagent bottle is covered, the plastic bottle lid and the edge of the bottle are pressed to produce plastic particles. In this case, a solid added may be completely dissolved, but a small amount of impurity particles are present in the mobile phase as a residue.

Filtration of the mobile phase through a 0.45 μm microporous membrane is an effective method for removing all particulate matter from the mobile phase. 0.2 μm microporous membranes are also available, but they are no more effective than 0.45 μm microporous membranes for this application, and their filtration rate will be slower, especially when the quality of reagents and water used in the laboratory is not Very good. It is recommended that laboratories stipulate in the preparation of their mobile phase preparation standard operating procedures (SOPs) that they can draw on the regulations of similar laboratories in the world, that is, mobile phase preparation requires only filtration when using HPLC grade liquid, and vice versa. It must be filtered before use. It is also important to use a sunken filter at the end of the infusion tube that connects the reservoir and the pump (commonly available in both molten glass core filter and microporous metal). This filter has a pore size of ≥10 μm, so it cannot replace the mobile phase filtration step, but it can remove dust from the system and ensure the reliability of the use of the reservoir and the infusion tube.

2 , the sample to be tested

The second source of particulate matter in the liquid chromatograph system is the sample being tested. Some laboratories prior to placing their samples on an autosampler tray (or manual injection), all samples were first filtered through a 0.45 μm syringe filter. This is a method to effectively remove particulate matter from the sample being tested. However, there is one point to be aware of in this process: if you use a syringe filter, it is impossible to get 100% of the sample to be tested through the filter, and there will always be more or less loss. Loss comes from such aspects as the adsorption of the filter membrane, the adsorption on the particles filtered by the filter, the leakage of the syringe filter and the syringe connection. If there is any loss, is the content or concentration of the analyte in the filtered liquid the same as the content or concentration of the original basic solution? This problem generally needs to be confirmed by experiments. Confirm this step is to increase the workload and cost. The use of filters is a consumption, and the price of each filter ranges from a few dollars to a dozen yuan. However, when doing residue analysis in video, the filtration step has become an indispensable step because the matrix is ​​mostly complicated. In the actual analysis work, the general inspection 2 each group of samples will bring an external standard, an added recovery or quality control sample, so as long as the signal-to-noise ratio obtained at the final detection can meet the detection limit requirements, this step can be taken. It is considered as a systematic error and ignored.

3 , the wear of the instrument system components

Finally, another major source of particulate matter in high performance liquid chromatography (HPLC) systems is the wear of the infusion pump seal and the injection valve rotating shaft. There are two different recommendations for wear replacement of infusion pump seals.

The first suggestion is that in general laboratory infusion pump seals typically have a service life of six months to one year, so it is recommended to replace these seals for six months or one year, and the laboratory should develop a regular preventive maintenance program based on this view. According to this view, the cost of replacing the gasket is lower than the cost of replacing the new column with the infusion pump gasket particles. Some infusion pumps have a glass core or screen that filters out particles from the pump seal in the flow path to prevent these particles from flowing to the column head with the mobile phase. If such a device is available, consult the infusion pump operating manual for the recommended interval for such filter cleaning or replacement.

Another suggestion is that the original seal has the best sealing effect and is likely to cause leakage of the mobile phase after replacement. Therefore, do not easily replace the gasket as long as it does not leak.

Both arguments have their own reasons. How to operate, it is recommended to communicate with the engineers of the instrument company. The instruments of each company are still somewhat different.

The seal of the autosampler rotary shaft wears out over time, but in my experience, even high-load rotary shaft seals can be used for several years. If your autosampler system has the ability to count the number of injections of the injection valve, you can set an alarm to alert you when the preset number of rotations has been reached. There has been a saying that the injector rotates up to 20,000 times, which is only 10,000 injections; but this does not seem to be the routine sample analysis life involved in the laboratory, and their actual service life will be longer. The rotating shaft seal will seep after wear, and the obvious feature is that the peak area value is relatively large after multiple injections of the same sample (RSD>5%). Of course, the seal of the infusion pump and the seal of the rotating shaft will increase the amount of abrasive in the mobile phase, accelerating damage to these components. In addition, if your daily mobile phase has buffer salts, such as phosphate buffer salts, the seal will wear faster.

Regardless of the source of the particles, they should be removed during the experiment. Line recommended a porous filter of 0.45 or 0.5 μm HPLC high performance liquid chromatography system, connected between autosampler and column, even if the use of a guard column. This in-line filter will be the filter plate for the baffle instead of the stud, and if a glass core filter plate is used, it is cheap and easy to replace (replaceable in a few minutes). If online filtration is used, the HPLC system will record the pressure value before the start of each batch of samples. When the pressure rises to a certain value, for example, 25% or 500 psi, the glass core filter plate should be replaced. After the replacement, the system will be restored to a few minutes. The value of the pressure.