Peak tailing can occur due to numerous reasons. The problem can be identified according to the following scheme:

● Mass overload: when injecting less sample amount (mass) either the peak becomes more symmetrical or resolves into two separate peaks. Use a more dilute injection sample to correct the situation. In fact, rounded peaks with a fronting end generally are a typical manifestation of an overloaded column.

● Secondary interactions: when injecting a neutral compound (acetophenone, toluene) the peak becomes symmetrical. Adjust the mobile phase pH in order to neutralize charged analytes.

For larger ID columns (>10 mm) radial temperature gradient can also cause peak tailing. In order to avoid such a problem, it is recommended to use a column oven.

If neither of the above applies, the tailing can also be caused by irregularities in the column packing process (preferential path), a void at the column inlet or by a partially clogged inlet frit leading to an irregular flow profile/path. If it is a badly packed column, empty and repack with a different slurry/solvent/pressure combination and retest to check if that corrected the problem. If it is a partially blocked frit, carefully change the frit making sure not to disturb the column bed surface and retest. The frit can also be removed, sonicated in Methanol and replaced in column fitting.

● Column temperature fluctuations. (Even minor variations allow the cyclic baseline to rise and fall. Refractive index and conductivity detectors, UV detectors at high sensitivity or indirect photometric mode are most commonly affected.)

● The non-homogeneous mobile phase. (Drift from temperature fluctuation to higher absorbance, rather than a cyclic pattern.)

● Contaminant or air build-up in the detector cell.

● Connected outlet line to the detector. (High-pressure gaps in the cell window, creating a noisy baseline.)

● Mobile phase mixing problem or alteration in flow rate.

● Slow column balancing, particularly when adjusting the mobile step.

● Mobile phase contamination, deterioration or from low quality solvents.

● Strongly preserved materials in the sample can be elucidated as very broad peaks which tend to be rising baseline. (The gradient analysis can make the problem worse.)

● The use of recycled solvents is not recommended.Unadjusted detector.

● Detector (UV) not mounted at the highest absorbance but the curve angle.

● Bubbles are generated inside the pump head

● The previous mobile phase is still in the pump head

● Bubbles are generated inside the pipe

● Check valve is not working properly

● Liquid leaks from the gap between the pump head and the fixed seat of the pump head, or from the cleaning flow path

● Liquid leakage from the flow path connection

● Flow path (partially) blocked

● The plunger sealing ring quickly wears out

● The one-way valve is installed in the pump head, and its working state directly affects the accuracy of solvent delivery. When abnormal infusion occurs, the one-way valve needs to be cleaned.

● The one-way valve is located in the pump head, the structure is installed under the main pump head a one-way valve, you can open the upper and lower valve body by random tools, and take out the one-way valve.

What are the signs of pump washer damage?

● Pressure instability under high pressure.

● Leakage of mobile phase from pump head. It generally reflects the change of sample retention time. A leaking gasket is like a pressure regulator, to a certain pressure of the high voltage line pressure will not go up, part of the liquid flow in the gasket part leakage.

● Pressure instability under high pressure.

● Leakage of mobile phase from pump head. It generally reflects the change of sample retention time. A leaking gasket is like a pressure regulator, to a certain pressure of the high voltage line pressure will not go up, part of the liquid flow in the gasket part leakage.

● The viscosity of the mobile phase is too high and contaminated. It is recommended to choose a suitable mobile phase and ratio, reconfigure, and use a 0.45 micron filter membrane for filtration.

● The buffer salt in the mobile phase causes blockage of the one-way valve. Set the flow rate to 5mL/min, loosen the exhaust valve, and purge.

● There is gas in the pump, set the flow rate at 5mL/min, loosen the exhaust valve and purge.

● The high-pressure sealing gasket is deformed, it is recommended to replace it with a new one.