Several problems of using high performance liquid chromatograph
1. Will the mobile phase in the column drain?
Many people doing chromatographic separation experiments have encountered such a situation that the mobile phase in the solvent bottle was sucked dry by accident and the mobile phase in the solvent bottle was inadvertently replenished, and the HPLC system stopped working.
Will this damage the column?
Has the pump drained all mobile phase from the column?
Can the column be used?
In fact, if the pump dries the mobile phase in the solvent bottle, it will not cause damage to the column. Even if the pump is filled with air, the pump will not exhaust the air into the column. Because the pump can only deliver liquid, not air.
In contrast, another situation that is more likely to happen is to forget to close the sealing caps on both ends of the column or the cap is too loose and the column dries out. Similarly, it is not easy for the entire column to dry up. It is likely that only a few millimeters at both ends of the column have dried. It takes a long time for the column to dry because all the solvent has evaporated.
Even if the column is really dry, it is not necessarily incurable. You can try to flush the column with a completely degassed solvent with low surface tension (such as methanol degassed with helium) to remove the gas. The lower surface tension helps to wet the surface of the filler; the degassed solvent should be able to dissolve and remove the gas trapped in the filler.
The column takes approximately one hour or more (at a flow rate of 1 mL / min) to be thoroughly infiltrated and returned to normal.
2. What issues should be paid attention to when using PEEK (polyetheretherketone) pipes and joints?
If you often need to change the flow path or replace the column of a different brand, it is very convenient to use the tubing and fittings made of PEEK material. PEEK tubing is easy to connect; PEEK fittings can be fixed by hand without using tools, and it is easy to adjust the length of tubing other than the cone hoop, which is convenient for connecting with different brands or specifications of chromatographic columns.
It should be noted that the piping of such materials is: PEEK is not compatible with halogenated alkanes and tetrahydrofuran. Although no obvious signs of the above solvents dissolving the PEEK material were observed, PEEK becomes brittle when it encounters the above solvents.
Another factor to consider is the pressure limit. Stainless steel tubes can withstand a pressure of 6000 psi, but PEEK tubes can only withstand nearly 4000 psi (but most HPLC application systems will not exceed 3000 psi).
When using PEEK joints, there is no need to worry about the solvent resistance of the joint, because the joint has little or no direct contact with the solvent. However, the pressure limit of the PEEK joint that is fixed by hand is lower than that of the stainless steel pipe. Therefore, when the pressure is too high, the joint may slide on the pipeline and cause dead volume or liquid leakage.
3. How to prevent the failure of the liquid phase pump To maintain the good performance of the pump, the system must be maintained clean, the quality of solvents and reagents must be guaranteed, and the mobile phase should be filtered and degassed. Several measures to prevent pump failure are listed below:
1). Use high-quality reagents and HPLC-grade solvents;
2), filter mobile phase and solvent;
3). Degassing;
4), vent the air when starting to use every day, and wash the buffer from the pump after the work is over;
5) Do not allow water or corrosive solvents to stay in the pump;
6). Replace the gasket regularly;
7). Add lubricant when needed;
8). Refer to other suggestions in the pump operation manual.
A pump in good operating condition should be:
The baseline on the chromatogram is stable;
Good retention time repeatability;
The pressure fluctuation is less than 2% during isocratic elution;
The pressure change during gradient elution should be slow and steady.
In order to eliminate the fault as soon as possible after the occurrence, the seal, check valve (inlet and outlet), pump head device, various joints, fuses and other parts should be always available, as well as replacement tools.
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