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The magnetic stirrer, also known as a magnetic mixer or a magnetic stir plate, is often found biology and chemistry laboratories working in research and development (R&D).
That said, magnetic stirrers can be used in numerous industries, including biotechnology, microbiology, healthcare, chemical, and food and beverage. It is one of the simplest devices to use to prepare mixtures, but is not generally capable of stirring large volumes of a sample.
In these cases, mechanical stirring is often required. This is achieved using devices like the overhead stirrer, which can mix, homogenize, suspend, or recirculate large volumes or high-viscosity substances.
Nonetheless, a magnetic mixer is a very dependable piece of laboratory equipment when a smaller quantity of mixing is necessary and the project can easily fit on a small area of your bench space.
In fact, they are often preferred over motorized stir units because they are typically quieter and more efficient. Stirrers are also capable of working inside a sealed vessel or system without having to be isolated.
Magnetic stirrers do not require external moving parts that typically break down over time and often experience little wear and tear.
There is some variety to the types of magnetic stirrers available. But, most setups consist of a base, stir bar, and a hot plate, which can be made of stainless steel. However, some parts may be made of chemical resistant materials, such as glass or Teflon™.
The stir bar is one such component that benefits from being chemically inert, as it is placed inside of the beaker containing a sample that may include chemicals or other corrosive materials.
Stirrers come in a variety of sizes and are available in single or multi-position configurations. They can operate with or without a motor, and employ the use of magnets to provide continuous, hands-free stirring within laboratory glassware, such as beakers or vials, placed on top of the base. Let’s look at this device’s design and it’s various benefits.
A magnetic stirrer operates using a single rotating magnet or a combination of stationary electromagnets. All magnets are stored below the device.
The magnet or magnets rotate using a motor and an electric current running through them, creating a rotating magnetic field that interacts with the magnetized stir bar placed within the beaker. This magnetic coupling controls the stirring speed of the device, which can be adjusted based on your needs, such as experiment goals or the viscosity of the sample.
As the magnetic field rotates, so does the stir bar, creating a vortex and stirring the contents of any vessel placed on top of the unit’s platform.
In general, stirring speed range varies from 100 to 2400 rpm, along for low and high-speed stirring; however, the device’s stirring capabilities and adjustable speeds mostly depend on manufacturer’s design. As the magnetic field rotates, so does the stir bar, creating a vortex and stirring the contents of any vessel placed on top of the unit’s platform.
A magnetic stir bar, also known as a flea, is typically made of a small magnet coated in PTFE (Teflon) or plastic. The coating is intended to be chemically inert so as not to react to the mixture the stir bar is immersed in.
This component is not very large, and ranges in size from a few millimeters to a few centimeters. Separately, a stir bar receiver, which is made of a small magnet attached to a long rod, may be used to retrieve the stir bar from inside the vessel.
The limited size of the stirrer bar means magnetic stirrers can only be used for tasks that involve smaller sample sizes, generally around 4 liters or less. The size also makes stirring any highly viscous substances difficult, and in some cases impossible.
Despite these limitations, magnetic bars are easy to clean and sterilize, and do not require any lubrication, which reduces the risk of contamination.
Magnetic mixers are often coupled with a hot plate to provide a source of heat. In general, the heating plate has a temperature range of 200-250°C, depending on the model, and comes with efficient temperature controls.
Hot plates create heat by running an electrical current through a medium with high electrical resistance, such as a metal coil. The heat provided is safer, gentler, and more controllable than a Bunsen burner.
Depending on the size of your experiment, either a single-position or multi-position magnetic stirrer will be optimal. As a stir bar can only stir so much, you may need multiple flasks to be running simultaneously to maintain efficiency.
In this case, a multi-position magnetic mixer is appropriate to use. These devices allow multiple vessels to be stirred simultaneously, and at different speeds. When dealing with one sample at a time, a single-position stirrer is adequate.
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