Pipette

A pipette is a fundamental laboratory instrument used to transport specific volumes of liquid. These tools are essential in biological and chemical research, where they often act as media dispensers.

Because scientific experiments require different levels of precision, many designs exist. Some are simple glass tubes, while others are highly complex electronic devices. The choice of pipette depends on the volume needed and the required accuracy. Precision is vital because even tiny errors in liquid measurement can change the outcome of an experiment.

Most common pipettes, known as air displacement micropipettes, operate through a specific mechanical process.

These devices use a piston-driven system to move liquid. Inside the pipette, a metal or ceramic piston moves vertically within an airtight sleeve. When a user depresses the plunger, the piston moves upward. This movement creates a partial vacuum in the space left behind. The liquid is then drawn into the chamber to fill that vacuum. The user can then dispense the liquid by allowing the piston to move back down. This method can handle volumes ranging from 0.1 μL to 1,000 μL.

There are several distinct categories of pipettes designed for different scientific tasks. Volumetric pipettes, or bulb pipettes, are used when extreme precision is required.

These tools have a large bulb and a single graduation mark to measure one specific volume, such as 20 mL or 100 mL. Graduated pipettes are long tubes with many marks to indicate different volumes. For much smaller tasks, researchers use micropipettes, which handle volumes under 1000 μL. There are also positive displacement pipettes. These use a plastic microsyringe to move liquid directly, which is helpful for viscous or volatile substances like DNA.

The history of the pipette shows a long evolution of design. Early scientists used simple glass tools, such as the Pasteur pipette.

Around or before 1877, Joseph Lister invented an early adjustable micropipette that functioned like a syringe. In 1957, Dr. Heinrich Schnitger patented a micropipette in Marburg, Germany. Later, Dr. Heinrich Netheler of the company Eppendorf began commercial production in 1961. The modern adjustable micropipette was further developed in 1972 at the University of Wisconsin–Madison by Warren Gilson and Henry Lardy. By 1984, Mettler-Toledo Rainin introduced electronic pipettes to the market.

Maintaining accuracy through calibration is a critical part of laboratory work. Calibration is the process of comparing a pipette to a known reference standard to ensure it measures correctly. The frequency of this task depends on the industry and the level of testing. For example, schools may only calibrate their pipettes annually. However, companies in the food or drug industries must perform calibration quarterly, every three months. Researchers in forensics or high-level research may need to calibrate their tools every single month to maintain strict standards.

Specialized pipettes exist for the most advanced scientific frontiers. At Brookhaven National Laboratory, scientists use a zeptolitre pipette to study crystallization. This tool uses a carbon shell with a gold-germanium alloy. In the field of microfluidics, researchers like Alar Ainla have developed pipettes made from polydimethylsiloxane (PDMS). These allow for constant control of a nanolitre environment.

Other tools, like the Winkler–Dennis gas combustion pipette, are designed to control chemical reactions using oxygen and an electric current. Even robots are now used to manipulate pipettes just as a human would.

Because pipetting is often a repetitive task, scientists must be mindful of ergonomics.

Using incorrect posture can lead to musculoskeletal disorders. One common error is the "winged elbow" technique, where the arm is held in a static, extended position. Since the human arm weighs about 6% of total body weight, this position puts significant stress on the neck and shoulder muscles. It also reduces blood flow and muscle strength. To prevent these injuries, electronic pipettes were developed to reduce mechanical strain, and specialized pipette stations can help control the depth of the tip.