Summary of the most complete failure of liquid chromatograph

High performance liquid chromatography system is mainly composed of liquid storage bottle, pump, injector, column, column temperature box, detector and data processing system. For the whole system, the column, pump and detector are the core components, and also the main parts prone to problems.
As a high-precision instrument, if it is not operated correctly in the process of use, it will easily lead to some problems. The most common problems are column pressure, drift and abnormal peak type. Today Titan chemical listed a few common fault phenomena, with the most possible suggestions, so that you can eliminate the fault one by one, regain confidence!
Phenomenon 1: the baseline is uneven. After flushing, it is normal, and then the plunger rod leaks liquid. After changing the sealing ring, it is normal. Then, when testing the sample, the pump makes a big noise, and the pump stops running immediately. After lubricating the pump, the noise disappears. After injection, the peak height is extremely low. After several times of testing, no peak appears at last. Why?
Suggestions:
1. Check whether the liquid circuit is normal and ensure that the flow and sealing are correct
2. Do not connect the column into the pure product to see if the detector responds. If not, the detector is out of order
3. Check whether your sample is normal
Phenomenon 2: the liquid chromatography six in injector was blocked recently, and the injection valve of the pump began to leak. Some people said that it was blocked after the injection without using methanol to clean the sample. I want to know whether it is necessary to inject several injections of methanol to clean after each sampling, and what is the cause of the leakage?
Suggestion: in fact, to know whether the six-way valve is blocked, you can clean it with organic phase when the pump is stopped. If it can be cleaned normally, it should not be blocked. If the solvent can not be put in, it should be blocked, or you can see if the leakage is loose.
Phenomenon 3: when a sample is connected into six needles by liquid chromatography, the peak area varies greatly, from high to low. Why?
Suggestions:
1. Sometimes bubbles will appear in the injector. If a sample is continuously injected at this time, the peak area will change from high to low. It will be OK to do more purge injector.
2. Use the standard sample to see if it is the problem of the sample; then check whether the column temperature, flow rate, injector and deuterium lamp have problems.
3. Check whether there are bubbles in the quantitative ring
4. Is there any leakage in the six-way valve, column interface and pipeline from pump to column interface
In fact, in the final analysis, there are two cases, either the reason for the sample or the reason for the instrument. If it is a sample, it is suggested to change other substances for test; if it is due to instrument, it may be the injector, quantitative ring, proportional valve and so on.
With common troubleshooting methods, it's too bad to collect them
1. If it is found that the pressure is very small during operation, there may be leakage in the connection of pipe fittings. Pay attention to inspection. When there is an error warning (the indicator light of each component is red), it is generally liquid leakage. There is solvent in one of the sensors. After the leakage is eliminated, wipe it dry. Click instrument / system off in the on line operation interface, and then click instrument / system on in the operation interface.
2. When connecting the column and the pipeline, attention should be paid to the tightening force of the screws, which may lead to the fracture of the connecting screws. Liquid leakage is easy to occur at the column joint, which may be that the pipe in the middle of the fitting is not tightly attached to the joint. The structures of pipelines and chromatographic column heads of different manufacturers are different, so it is better not to mix them. Peek tube and movable joint can be used if necessary;
3. If it is found that the pressure is very high during the operation, the pipeline may be blocked. The chromatographic column should be removed first, and then the segmented exclusion method should be used to check to determine where the blockage is, and then solve the problem. If the protective column or chromatographic column is blocked, small flow of mobile phase or small flow of isopropanol can be used for flushing, and the method of small flow back flushing can be used (the new column is not recommended). If the column is still not unobstructed, the column needs to be replaced;
4. During operation, the pump stops automatically, which may be due to the pressure exceeding the upper limit or the mobile phase being used up;
5. There are few samples in the sample bottle, and the injection probe of the automatic sampler can not reach the liquid level. The injection height of the injection probe can be lowered. Attention should be paid not to make the injection probe touch the bottom of the bottle when setting. The micro sample bottle should be used for micro sample analysis;
6. The injection probe of the automatic sampler is not aligned with the bottle mouth of the sample bottle, so it needs to be repositioned.
7. The pump pressure is unstable or the flow rate is not accurate, which may be the problem of plunger rod seal ring or seal wash washer, which needs to be replaced;
8. The possible causes of irregular noise at baseline may be that the system is unstable or does not reach chemical equilibrium (if ion pair reagents are used, sufficient time and solvent volume are required for the first use, so that the chromatographic column can reach sufficient equilibrium), the mobile phase is contaminated (replace the mobile phase, clean the reservoir and filter, flush and rebalance the system), and the chromatographic column is contaminated (for evidence) The possible reason is that the chromatographic column of the system is replaced or a similar column with good performance is used), and the detector is unstable;
9. The short-term regular noise may be caused by unstable pump pressure or pump pulse, improper adjustment of solvent (such as the mutual solubility of two solvents), loose or blocked pump inlet pipeline, dirty pump, worn pump plunger and unstable detector;
10. Long term regular noise may be caused by unstable room temperature (no column incubator) or improper use of column incubator;
11. Baseline drift may be caused by system instability or failure to reach chemical equilibrium, unstable room temperature (without column incubator), mobile phase contamination or decomposition, column contamination, leakage of detection cell, system leakage, loss of stationary phase (alternative mobile phase and chromatographic column), wrong wavelength selection (solvent absorption), too long sample component retention (cleaning chromatography with solvent with appropriate strength) The detector is unstable;
12. The retention time of each injection is not repeated, which may be caused by the system instability or not reaching chemical equilibrium, unstable pump pressure or pump pulse infusion caused by bubble and wear of various parts, too large sample volume or sample concentration, the balance is destroyed, the solvent ratio is not suitable, and the column is polluted;
13. There is no peak, which may be caused by the wrong selection of the detector, the use of the wrong mobile phase and the degradation of the sample;
14. The chromatographic peak ratio was small as expected. The possible causes were injection volume error, detector lamp failure, injection problems (wrong bottle number, improper injection volume, wrong injection, needle blockage);
15. The possible reasons are that the injection volume is too large or the sample concentration is too high, the filter, the inlet of the protection column, the inlet of the column or the connecting pipeline are partially blocked, the detector time constant is set incorrectly, the injector has problems (such as valve leakage, needle blockage or damage), the column or protective column is contaminated, the sample solvent is too strong for the mobile phase, the wrong column is used, and the temperature changes;
16. The possible reasons for the double peak / shoulder peak are that the protective column or the column inlet is partially blocked, the column or protective column is polluted, the performance of the column decreases, the protective column fails, the injection volume is too large or the sample concentration is too high (sample overload), and the balance is broken;
17. The front peak may be caused by too large injection volume or too high sample concentration (sample overload), and the equilibrium is broken. For the mobile phase, the sample solvent is too non-polar (for the reversed phase column), the column or protective column is polluted, the column performance decreases, and the protective column fails;
18. The possible causes of tailing peak are contamination of column or protection column, degradation of column performance, failure of protection column, injector problems (such as valve leakage), and wrong setting of detector time constant;
19. Ghost peak may be caused by contamination of mobile phase, degradation or mixing of impurities during sample pretreatment, effluent from previous injection, improper cleaning of sample quantizing tube, dirty syringe, contaminated column, contaminated injection device, and change of stabilizer / stabilizer in mobile phase. The water film and oil film shell are marked.
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