The accuracy of a serological pipette first comes from its precise mechanical structure design. Taking an air pipette as an example, its core components include a piston, an air cushion, a pipette tip, and a graduated tube. The piston changes the volume of the air cushion through mechanical movement to form a negative pressure to inhale the liquid, while the graduated tube ensures the accuracy of the measured volume through precision machining. The sealing of the piston and the air cushion directly affects the stability of the negative pressure, which in turn determines the accuracy of liquid inhalation. Studies have shown that high-quality sealing materials and processing technology can control the piston leakage rate to an extremely low level, ensuring that the measurement error is less than 0.5%.

As a component that directly contacts the liquid, the material and inner wall smoothness of the pipette tip are crucial to accuracy. Disposable polystyrene pipette tips are widely used due to their chemical stability and low adsorption, while pipette tips with specially treated inner walls can further reduce liquid residue and improve measurement accuracy. In addition, the conical design of the pipette tip needs to be closely matched with the pipette to avoid leakage or bubbles caused by assembly gaps.

Even with a sophisticated mechanical structure, incorrect operation can still lead to significant errors. Therefore, standardized operating procedures are the key to ensuring the accuracy of serological pipettes. During the aspiration stage, the thumb should be released slowly and steadily to avoid the liquid impacting the plunger due to excessive speed, causing the corrosive liquid to flow back. Pre-wetting the tip is an effective means to improve the accuracy of high-viscosity liquid measurement. By repeatedly aspirating and hitting the liquid to form a uniform liquid film on the inner wall of the tip, the volume deviation caused by the "liquid film effect" can be significantly reduced.

Pay attention to the control of angle and speed during the discharge stage. Stick the tip to the wall and keep a certain tilt angle, press to the first gear to pause, wait for the remaining liquid to gather, and then press to the second gear to completely discharge, which can minimize the residual liquid on the inner wall of the tip. For viscous or volatile liquids, it is recommended to use the reverse pipetting method, that is, press to the second gear when aspirating and press to the first gear when hitting, so that some liquid remains in the tip to compensate for the volume loss caused by evaporation or adhesion.

Calibration is the core link to ensure the long-term accuracy of serological pipettes. The laboratory needs to calibrate the pipette regularly using an analytical balance to verify the pipette's measurement accuracy by weighing the weight of the pure water taken and calculating its volume. For example, the weight of 1mL of distilled water at 20°C is 0.9982g. If the weighing result deviates by more than 0.5%, the pipette needs to be adjusted.

Adjustable pipettes change the reading of the reading window by rotating the adjustment knob, but be aware of the range limit. Turning the button out of the range may cause the mechanism to get stuck or even damaged, so when calibrating, make sure that the set range is within the rated range of the pipette. For high-precision experiments, it is recommended to use a multi-point calibration method to cover the commonly used range of the pipette to fully evaluate its linearity and repeatability.

Environmental factors have a significant impact on the accuracy of serological pipettes. Temperature changes can cause the volume of liquids to expand or contract, so it is necessary to operate at room temperature (15°C-25°C) and ensure that the liquid taken has fully equilibrated to the ambient temperature. For high-temperature or low-temperature samples, rinsing the pipette tip may reduce the accuracy of the operation. In this case, the temperature gradient should be reduced by pre-cooling or pre-heating the pipette tip.

Humidity and air pressure fluctuations may also affect the performance of the pipette. In a high-humidity environment, water droplets may condense on the inner wall of the pipette tip, resulting in a larger volume; and air pressure changes will change the negative pressure strength of the air cushion, thereby affecting the amount of liquid inhaled. Therefore, the laboratory should be equipped with a temperature and humidity control system, and high-precision experiments should be suspended when the air pressure fluctuates greatly.

The materials and processes of the core components of the pipette directly affect its stability. Pistons and connectors are usually made of metal or composite materials (such as ceramics or synthetic polymers). The metal process is not mature enough in China, which is prone to fluctuations between parts and affects the long-term accuracy of the pipette. High-quality assembly processes can reduce mechanical errors. For example, Gilson pipettes provide a lifetime free cleaning and calibration service to ensure that the accuracy of each gun remains stable.

The material and processing accuracy of the pipette tip are also critical. Polystyrene tips are widely used due to their chemical stability and low adsorption, but the roughness of the inner wall needs to be controlled below the micron level to avoid liquid residue. In addition, the conical design of the tip needs to fit closely with the pipette. Excessive assembly gap will cause leakage or bubbles, which will affect the measurement accuracy.

Regular maintenance is a necessary measure to ensure the accuracy of serological pipettes. The tips and pipettes need to be cleaned in time after use to avoid residual liquid from corroding internal parts. For metal parts, it is recommended to use special lubricants for maintenance to reduce mechanical wear. The storage environment of the pipette needs to be dry and ventilated, avoiding direct sunlight and high temperature to extend its service life.

The setting of the calibration cycle needs to be determined according to the frequency of use and the experimental accuracy requirements. For pipettes used frequently, it is recommended to calibrate once a month; for low-frequency equipment, it can be calibrated once a quarter. In addition, the pipette needs to be recalibrated to ensure its accuracy after a severe collision or long-term non-use.