Air displacement pipettes and external piston pipettes, as indispensable precision tools in the laboratory, each play an important role in the fields of scientific research and testing with their unique working principles and applicable scenarios. Although both are pipettes, there are significant differences in design concepts, operation methods, performance and applicable liquid types.

1. Working principle 1. Air displacement pipette: (1) Use air pressure to push the piston for pipetting. (2) Through the power of compressed air, the piston in the pipette is pushed in the direction of pipetting to achieve the pipetting effect. (3) When the pipette catheter is inserted below the liquid level, the compressed air increases the internal pressure of the pipette, forming a negative pressure, thereby aspirating the liquid. (4) When the pipette catheter is inserted above the liquid level, air is released to reduce the internal pressure of the pipette, forming a positive pressure, thereby discharging the liquid. 2. External piston pipette: (1) Use human hands or mechanical force to push the external piston of the pipette for pipetting. (2) Move the liquid in the pipette by manually pushing the external piston. (3) The piston is in direct contact with the liquid and there is no air column.

2. Application scenarios 1. Air displacement pipette: (1) Suitable for workplaces that require pipetting in high-viscosity or high-concentration liquids. (2) Commonly used in chemical and biological experiments that require fast and precise pipetting. (3) It is also suitable for operations such as ventilation and replacement of solutions in bottles. 2. External piston pipette: (1) Commonly used for routine pipetting work in biological or chemical experiments. (2) It is especially suitable for pipetting liquids with high viscosity, easy volatility, easy foaming and other problematic liquids.

3. Advantages and disadvantages 1. Air displacement pipette: Advantages: high precision, fast pipetting speed, suitable for high viscosity or high concentration liquids, and can prevent liquid contamination during operation. Disadvantages: It requires an air source to work properly and the cost is relatively high. 2. External piston pipette: Advantages: low cost, easy to learn and operate, and does not require special tools or air sources for operation. Disadvantages: Relatively low accuracy, not suitable for high viscosity or high concentration liquids, and easily contaminated by the external environment.

4. When choosing a pipette, it is recommended to take the following steps: 1. Clarify the experimental requirements: Understand your experimental type, liquid characteristics, and required pipetting accuracy and speed. 2. Compare different brands and models: Check out different brands and models of pipettes to learn about their performance features, prices, and user reviews. 3. Trial experience: If conditions permit, you can try out several pipettes to feel their operating feel, accuracy and comfort. 4. Consider your budget: Choose the right pipette based on your budget. 5. Refer to user reviews: Check the reviews and suggestions of other users to understand the actual use effect of the pipette.

Air displacement pipettes and external piston pipettes have their own advantages, and they show their respective advantages in different experimental environments and liquid handling needs. Air displacement pipettes have become the first choice of many scientific researchers and laboratories due to their high precision, fast response, and ability to handle high-viscosity, volatile liquids. External piston pipettes have won wide recognition and application due to their simple structure, convenient operation, high cost-effectiveness and suitability for routine pipetting tasks.

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