Third-party chemical testing center

Nanjing Aikang Quanxin Analysis and Testing Center currently possesses a series of large-scale analytical instruments, including domestically advanced high-resolution 400M nuclear magnetic resonance spectrometers, a full set of Agilent series liquid chromatography-mass spectrometers, gas chromatography-mass spectrometers, high-performance liquid chromatographs, gas chromatographs, and various physicochemical analytical instruments.
When operating high-performance liquid chromatography, have you ever been frustrated by the constant appearance of bubbles? During the operation of high-performance liquid chromatography, if bubbles appear in the mobile phase, the entire workflow cannot proceed.
Why is it that after ultrasonic shaking of the mobile phase for an hour, bubbles do not appear on sunny days but appear on cloudy or rainy days? This is because on cloudy or rainy days, the atmospheric pressure decreases, causing the air dissolved in the mobile phase to become supersaturated (on sunny days, the higher pressure prevents saturation). When the high-pressure pump draws the mobile phase, the air precipitates, forming bubbles.
Why is there still air in the mobile phase after ultrasonic shaking for an hour? This is because shaking at atmospheric pressure is not effective in驱赶空气.
What would happen if the bottle containing the mobile phase is subjected to vacuum while undergoing ultrasonic shaking? The effect is excellent: in just 1 minute, almost all the air in the mobile phase is removed. Mobile phase treated this way will not produce bubbles even on cloudy or rainy days. It is also time-saving, eliminating the need for half-hour or hour-long ultrasonic shaking sessions, and the results are highly effective.
The presence of bubbles can cause sharp noise peaks on the chromatogram, and in severe cases, reduce analytical sensitivity. When bubbles grow and enter the flow path or chromatography column, they can slow down or destabilize the flow rate of the mobile phase, causing baseline fluctuations.

There are three main reasons for the above phenomena: First, the mobile phase solution often contains bubbles due to dissolved oxygen or mixed air. Second, air in the flow path was not thoroughly驱赶干净 when the system started working. Third, air was inadvertently mixed in when injecting the sample.

Common degassing methods include the following:
1. Helium Sparging Degassing Method: Uses helium, which has lower solubility in liquids than air. Under 0.1Mpa pressure, helium is bubbled through the mobile phase at a flow rate of about 60ml/min for 10-15 minutes to驱除溶解的气体. This method is suitable for all solvents and has good degassing效果, but due to the high cost of helium in China, it is less commonly used.
2. Heating Reflux Method: This method has good degassing效果.
3. Vacuum Degassing Method: A miniature vacuum pump can be used to reduce pressure to 0.05-0.07MPa to remove dissolved gases. Obviously, using a water pump connected to a filtration flask and a G4 microporous glass funnel can simultaneously accomplish the dual tasks of filtering mechanical impurities and degassing. Since vacuum degassing can cause changes in the composition of mixed solvents, this method is suitable for degassing single-solvent systems. For multi-solvent systems, degassing should be performed before mixing to ensure the比例不变.
4. Ultrasonic Degassing Method: This is the most widely used degassing method in laboratories. The prepared mobile phase, along with its container, is placed in an ultrasonic water bath for 10-20 minutes for degassing. This method is simple to operate and generally meets the requirements of daily analysis.
5. Online Vacuum Degassing Method: A vacuum degassing device is串联到 the solvent reservoir system, combined with a membrane filter, enabling continuous vacuum degassing of the mobile phase before it enters the infusion pump. This method has significantly better degassing效果 than the above methods and is suitable for multi-solvent systems. Secondly, before starting the liquid chromatography system, a syringe can be connected to the purge valve of the constant flow pump to draw in the mobile phase and驱赶干净 the air in the flow path. Third, care should be taken to expel air from the sample syringe before injection.
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