Pipetting Classroom: Air Displacement Pipettor

In scientific research, an indispensable tool in various experimental stages is the pipettor. The advent of the pipettor has completely revolutionized the way liquid is handled in scientific research, and it remains the primary tool for liquid handling.

What is Air Displacement Pipettor

It is based on the principle of air displacement (Air displacement). This liquid handling technology is the most mature and widely used micro-liquid handling technology today, with many automated liquid handling systems also based on this principle.

The Air Displacement Pipettor is mainly composed of three parts: the piston, the pipettor chamber, and the disposable tip. The piston is responsible for the up and down movement controlling the internal pressure change in the pipettor chamber, the disposable tip is used to store the drawn sample liquid, and the pipettor chamber maintains the airtightness during the pipetting process. Ensuring a high degree of seal between the pipettor components is crucial to the pipettor's performance.

The Air Displacement Pipettor is divided into automatic pipettors and manual pipettors. Whether in automated liquid handling systems or manual pipettors, the principle is to accurately control the distance moved by the piston within the device, driving air displacement to achieve liquid distribution.

Using an Traditional Air Displacement Pipettor for Liquid Handling Process

Firstly, by pressing the button or driving the plunger with a motor to move the piston down, the air inside the piston chamber is expelled, creating a vacuum in the sealed chamber by the vertical movement of the metal or ceramic piston. Upon releasing the button or motor drive, the piston moves vertically upwards, reducing the internal pressure of the pipettor, causing the external liquid at the tip end to enter the tip under atmospheric pressure until the internal and external pressures of the pipettor are balanced. When the piston moves down, the internal pressure of the pipettor rises, expelling the liquid from the tip, thereby achieving the function of liquid release.

Two Techniques for Using an Air Displacement Pipettor

Pipetting technique is one of the most important factors in providing accurate volumes, yet it is often overlooked. Inadequate training, incorrect operation, and lack of understanding of sample properties can greatly impact experimental results and reproducibility.

There are two different but powerful techniques when using an Air Displacement Pipettor: forward pipetting and reverse pipetting. These two techniques have the same pipetting cycle but differ slightly in certain steps. The main difference between these two techniques depends on the nature of the sample and the temperature of the sample during operation. In the pipetting process, forward pipetting allows for accurate volume transfer, while reverse pipetting is recommended for handling challenging liquids (such as those that are viscous or dense).

In conclusion, micro-liquid handling technology based on air displacement offers high accuracy and precision with a simple structure, stable performance, and ease of operation, making it suitable for most pipetting operations. However, due to its reliance on the movement and compression of air, pipetting accuracy can be affected by environmental conditions, the characteristics of the liquid, and the user's technique.