Definition
A laboratory pipette is a manual or electric device used to accurately transfer trace amounts of liquid, and its operation is based on the principle of air displacement or forward displacement. It is usually composed of a handle, a volume adjustment mechanism, a tip connection rod and a disposable tip, and is one of the basic tools in analytical laboratories such as chemical, biological, environmental and food laboratories.
Principle
The working principle of pipettes is mainly divided into two types: air displacement type and forward displacement type. The air-displaceable pipette is moved through the cylinder by a piston to create negative or positive pressure to draw or drain the liquid, with a column of air in between. This mode is suitable for conventional aqueous solutions, and its volume transfer accuracy is affected by liquid density and vapor pressure, which can be described by the following relationship: P1V1 = P2V2, where P represents pressure and V represents air column volume. Forward displacement pipette pistons are in direct contact with liquid, eliminating air separation and are suitable for high viscosity, high vapor pressure, or foaming liquids.
Measurement method
The performance of pipettes is usually evaluated by measuring accuracy and precision. Accuracy refers to the proximity of the volume of pipetting liquid to the set volume, and precision refers to the consistency of multiple volumes of pipetting volume. According to international standards, the commonly used measurement method is the gravimetric method, which calculates the actual volume by weighing the mass of the pipette water and combining it with the density of the water at ambient temperature. The measurement process is carried out in an environment with controlled temperature, humidity and air pressure, and a calibrated analytical balance is used.
Influencing factors
The accuracy of pipetting is influenced by several factors. In terms of operation technology, including suction and discharge speed, tip immersion depth, discharge angle, and whether there is pre-lubrication. Environmental conditions such as temperature, air pressure and humidity can affect liquid evaporation and air expansion. In terms of liquid properties, viscosity, density, and surface tension can lead to volume errors. In addition, the calibration status of the pipette itself, the match between the tip and the connecting rod, and the wear are also factors to consider.
Applications
Laboratory pipettes are widely used in fields that require precise handling of liquids. In biochemistry, it is used to prepare reaction systems and sample dilutions. In molecular biology, he participated in nucleic acid extraction and PCR system construction. In environmental monitoring, it is used for standard solution preparation and sample aliquoting. In food analysis, assist in nutrient content detection and additive addition. Its application scenarios cover a variety of experimental links from basic teaching to cutting-edge scientific research.
Selection considerations
When selecting a pipette, multiple parameters need to be evaluated comprehensively. The volume range should match the commonly used transfer volume of the experiment, the fixed volume pipettes have high precision, and the adjustable range pipettes have good flexibility. Air displacement type or forward displacement type is selected according to the liquid properties. Operating comfort and ergonomics affect the level of fatigue during prolonged use. Electronic pipettes help standardize operating procedures and are suitable for high-throughput applications. Additionally, ensure that the instrument meets relevant national or international standards and consider the availability of calibration services.