Definition
A pipette is a laboratory instrument used to accurately transfer trace amounts of liquid, commonly used in biochemistry, molecular biology, clinical diagnostics, and drug discovery. It realizes the quantitative suction and distribution of liquids within a specific range of quantities by manual or electric means, and is one of the basic tools for routine laboratory operations.
Principle
The working principle of pipettes is primarily based on air displacement or direct displacement mechanisms. The air displacement pipette moves through a closed air column through a piston to create negative or positive pressure, which drives the suction and discharge of liquid. Direct displacement pipettes are pipetted through direct contact with the liquid with a piston and are suitable for high viscosity or volatile liquids. The accuracy of the volume transfer can be roughly described by the following relation: V = A × L, where V represents the transfer volume, A represents the piston cross-sectional area, and L represents the piston displacement distance.
Measurement method
The performance of pipettes is usually evaluated according to international standards such as ISO 8655 by gravimetric analysis. This method uses an analytical balance to weigh the mass of dispensed distilled water from a pipette, combined with the water density at ambient temperature, to calculate the actual volume, and compare it to the set volume to determine accuracy and precision. The measurement process should be carried out under controlled temperature and humidity conditions, taking into account the correction of factors such as evaporation.
Influencing factors
The performance of pipettes is affected by a variety of factors. In terms of operation technology, including pipetting speed, angle and tip matching; Environmental conditions such as temperature, air pressure and humidity may cause liquid evaporation or thermal expansion and contraction; Liquid properties such as viscosity, density, and volatility can also affect transfer accuracy. Additionally, regular calibration and maintenance of instruments are critical factors, as long-term use can lead to component wear and performance.
Application
Pipettes are widely used in life sciences, chemical analysis, environmental monitoring, and food inspection. In molecular biology, it is used for PCR reaction system preparation; In cell culture, it is used to add culture media or reagents; In clinical laboratories, for aliquoting serum or plasma samples. Its application scenarios require the instrument to maintain reliable repeatability and accuracy in the trace range.
Selection
When selecting a pipette, consider the range of volume, accuracy requirements, frequency of operation, and liquid properties. For conventional aqueous solutions, air displacement pipettes are widely applicable. When dealing with highly viscous or volatile liquids, a direct displacement type may be more suitable. Electronic pipettes help reduce the burden of repetitive operations and are suitable for high-throughput scenarios. In addition, attention should be paid to the ergonomic design of the instrument to reduce the risk of fatigue due to long-term use and to ensure the sustainability of its calibration services and accessories supply.