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Pipettor: How It Works

A pipettor is a simple hand-operated tool used to transport small volumes of fluids from one place to another. These devices come in various sizes and styles, but they all work on the same principle: applying negative pressure on a fluid-filled tip causes fluid to be drawn up into it. Pipettors are most commonly used by scientists and lab technicians to transfer reagents from one place to another, or to dispense precise amounts of liquid onto a reaction plate.

Since the first glass pipettes were developed in the 17th century, these devices have become an indispensable part of work in laboratories worldwide. They are inexpensive, simple to use, and safe enough for even children to operate.

How does it work?

A typical pipettor consists of a plastic or metal handle and an attached plunger. There is also a dial or digital counter on the face of the device, which measures the volume of fluid that has been aspirated. Some models can be enclosed in disposable tips to reduce contact with chemicals and prevent cross-contamination from one experiment to the next.

The science behind these devices is rather straightforward. As the tip of a pipette comes into contact with fluid, it forms an airtight seal around the surface of that fluid, creating suction (negative pressure) that draws up some amount of that liquid into its chamber. The inner diameter or plunger determines how much is drawn up, so it’s important for users to calibrate their pipettors before performing any experiments.

A positive displacement pipettor is different from an air displacement pipettor in how the fluids are drawn into the device. It uses a positive plunger that pushes the fluid inside of the device. Air displacements use an open vacuum, where a vacuum is used to pull fluid into the device.

How to use it?

To use a pipettor, a user first selects an appropriate tip and inserts it into the end of the plunger. The desired volume of liquid is then drawn up into the tip by pulling back on the plunger until it reaches that level. It is important to set the right volume on the dial before beginning a new experiment, because the plunger should never go above or below that level.

Once a tip has been filled to the desired amount, it can be released by pushing down on the plunger and pressing it firmly against a flat surface. The user should always make sure his hands are clean when operating a pipettor, and he should never touch the tip itself. To keep from contaminating samples or causing cross-contamination, these devices should always be used with disposable tips that fit over the end of the plunger like a collar.

To dispense fluid onto an experiment plate, users will first need to make sure their hands are clean and that they’ve removed the tip from the plunger. The desired volume of liquid is drawn up into the tip by pulling back on the plunger, and it’s important to keep a firm grip on both parts throughout this step.

Once all of the air has been removed from the tip, the user will then need to remove it from its collar. The tip is next pressed firmly against the reaction plate and slowly released. At this point, any fluid that was drawn up into the tip will be deposited onto the plate in a uniform stripe.

Modern pipettors can be used with both manual and electronic controls. Some of them come equipped with digital dials that count down the volume as it’s being measured, which makes it much easier for users to see when they’ve reached the desired amount. There are also pipettors that can be programmed with a preset volume and will automatically stop dispensing liquid at that level, which allows them to be used for automated experiments.


Clare Louise