Discover the Science Behind Magnetic Stirrers

In laboratories, stirring is an essential but tedious task. Fortunately, this necessity was revolutionized in 1917 with the invention of the magnetic stirrer. But, you may ask, 'How does a magnetic stirrer work?' This question leads us to explore the mechanics behind this necessary tool, one that ensures scientists no longer spend countless hours stirring by hand.

Understanding how a magnetic stirrer works also gives insight into the efficient and precise nature of a laboratory. 

“Magnetic stirrers embody the mindset of innovation that is used to drive scientific discoveries forward,” says Gordana Nastasic, Laboratory Applications Manager, Pipette.com. “Though simple in design, their profound influence on laboratory efficiency and collaboration are critical.”

In this article, we’ll explain what this laboratory staple is, describe its components, and share popular features of modern stirrers useful in labs.

What is a Magnetic Stirrer?

A magnetic stirrer is a laboratory instrument designed to mix liquids using a rotating magnetic field. This field causes a magnetic stirring bar, submerged in the liquid, to spin rapidly and mix the contents. 

One of the main advantages of a magnetic stirrer is its ability to automate stirring of solutions. This means technicians and scientists can work on other tasks while the stirrer mixes a solution while unattended. It also allows for mixing of solutions at high speeds that isn’t possible to do by hand.

However, they are generally unsuitable for mixing large volumes or high-viscosity substances and are best suited for bench-scale experiments.

Magnetic stirrers are commonly used in various fields, including the food, chemical, and biological industries. 

Components of a Magnetic Stirrer 

The setup of a magnetic stirrer comprises several key components that work together to ensure effective and efficient mixing of liquids. These components include:

• Stir plate: This is where the flask or container of liquid will sit.
• Magnet/magnetic coil: Below the stir plate lies a magnet or magnetic coil. It is responsible for generating a rotating magnetic field which is what creates the stirring action.
• Stir bar: The stir bar is a magnet. It is often pill-shaped but is found in a variety of shapes, coating materials, and sizes. 

It is placed in the flask or vessel where the solution is contained. When the stir plate is turned on, the stir bar will spin, creating a vortex in the liquid as it moves, thereby stirring the liquid.

Source

Many magnetic stirrers available today incorporate a hot plate. Stirrers with a hotplate first appeared in 1939. This allows the device not only to stir but also to heat the liquid, making it an indispensable tool for experiments that require temperature control alongside agitation.

The apparatus is used to mix liquids rapidly and thoroughly, with minimal risk of contamination, in a wide range of industrial, chemical, and biological applications.

How Do Magnetic Stirrers Work? The Science Behind Them

The science behind today’s popular stirrers revolves around the principles of magnetism and fluid dynamics. 

Inside the stir plate, either a rotating magnet or a series of electromagnets generate a rotating magnetic field. This field is carefully controlled to rotate at varying speeds, which directly influences the movement of the magnetic stir bar placed within the liquid. 

As the field rotates, the stir bar aligns magnetically and spins, creating a vortex within the liquid that ensures thorough mixing.

Magnetic Stirrer Uses

Magnetic stirrers are used in a number of applications in all kinds of laboratories including research, analytical, and industrial labs, as well as in others. They can be used anywhere a low-viscous solution needs consistent, continuous mixing. 

Examples of how stirrers are used in labs include:

• Analytical titrations. Titration is an analytical chemistry method used for quantitative analyses and is a common assay used for quality control in. Magnetic stirrers are crucial for determining precise and accurate titration results as they ensure the assay's reactants mix thoroughly.
• Reagent preparation. Preparing reagents for use in labs usually involves mixing different solutions together or dissolving a solid in a liquid. Magnetic stirrers ensure reagents are uniform solutions that have an equal distribution of components throughout.

Features of Magnetic Stirrers

Multiple types of magnetic stirrers can be found in a scientific laboratory. They range in size, features, functions, and styles. However, the principle behind a magnetic stirrer is always the same: to facilitate consistent, fast, automated stirring action. 

The difference between magnetic stirrers comes down to a lab's individual needs and solution mixing and stirring requirements. A list of common features to explore in a new magnetic stirrer are below.

Mini Magnetic Stirrers

Mini, or single-vessel, magnetic stirrers are small devices that can easily sit on a benchtop without cluttering the space. They are for stirring small volumes in a single vessel. The Benchmark Minimag magnetic stirrer, for example, has a footprint of less than 5 inches and can handle stirring volumes up to 1.5L.

Hot Plate Stirrers

Temperature control is vital for dissolving solids, chemical assays, and sample preparation. Most magnetic stirrers today are equipped with a heating element in addition to its magnetic capabilities.

Temperature ranges vary depending on the magnetic stirrer. Some have simple analog heat settings expressed in numbers, similar to a cooktop range, while others have digital settings that allow more control over temperature output. This option from IKA offers good mixing and digital temperature control.

Timer

Being able to work on other tasks while a solution mixes is a key benefit of magnetic mixtures. To aid this convenience further, you can find magnetic stirrers with timers. These devices will automatically shut off when scheduled to. This helps prevent overmixing and overheating of solutions.

Capacity

For busy and productive labs, having to mix multiple solutions simultaneously is a reality. It’s essential to have equipment that can handle the lab's needs and demands. For labs that need to mix several solutions simultaneously on a regular basis, selecting a stirrer that can accommodate multiple vessels at once is beneficial.

Magnetic stirrers with multiple positions are ideal for this purpose. They ensure that multiple vessels can be stirred at once using the one magnetic stirrer, allowing labs to ensure continuous productivity.

An example of a magnetic stirrer that can accommodate up to 10 vessels is here. However, stirrers most commonly have synchronous stirring ability, meaning stirring speed cannot be adjusted for each vessel.

Tips for Using Magnetic Stirrers Effectively – Every Time

While the science and practice of using a magnetic stirrer is relatively straightforward, there are certain nuances and factors to consider so you always get the effect you’re aiming for with a magnetic stirrer.

Vessel Selection

Not every vessel or container can be used with a magnetic stirrer. A vessel’s shape, size, construction material, and liquid volume within the vessel all need to be compatible for the use of a magnetic stirrer apparatus to be safe and effective. The following practices should always be followed when selecting a vessel to use with a magnetic stirrer.

• Solution volume. Make sure the vessel is large enough to safely hold the solution to be mixed. The force from the magnetic stirrer creates a vortex that pushes the solution up the sides of the container and could potentially spill over the sides of the container if the speed was too high.
• Vessel shape. Erlenmeyer flasks are the most common type of vessel used when operating a magnetic stirrer. The wide bottom provides enough space for the solution to stir effectively and the conical, narrow neck helps prevent the solution from spilling out. If a standard flask is used, keep the solution volume and stirring force low to prevent spillage.
• Container material. First, your container material must be non-reactive with the solution you’ll be stirring and the magnetic stir bar that will be added. Glass is best. Magnetic materials will not work. Plastic containers should be avoided as they lack the stability and durability of lab glassware.
• Vessel bottom. Always use a container that has a smooth, flat bottom. A container with a raised and rounded bottom (think of the rounded bottom of a wine or reagent bottle) will interfere with the stir bar’s ability to stir and you won’t be able to mix your solution properly. Erlenmeyer flasks, volumetric flasks, and standard beakers should be your go-to choice.

Stirring Speed

How fast (or how slow) you stir your solutions will depend on the application you’re working with. The speed and force needed should always be evaluated and assessed during each use, however, there are certain speeds, measured in RPMs, that are generally acknowledged as standard speeds for certain applications.

For microbiological and biotechnical applications, speed range (RPM):

• Aeration of bacteria cultures, 200-350 RPM
• Growth of bacteria cultures, 300-450 RPM

For dissolving nutrient media, intensive, speed range (RPM):

• Aeration of bacteria cultures 350-500

For routine laboratory work, speed range (RPM)

• Prevent accretion of suspended matter 150-250
• Titration 250-400
• Dissolving solids 350-700

Troubleshooting Issues with Magnetic Stir Bars

Every new lab technician has experienced the startling noise of a stir bar suddenly shifting from a smooth swirl to a jerky, wall-bouncing implement. (Think of an energetic jumping bean!). They quickly learn that there’s more to operating a magnetic stirrer than setting a speed and walking away. 

When stir bars misbehave, it’s likely due to one the following reasons:

• If the rotation of the magnetic stirring bar is uneven or jerky, the reaction between the alternating magnetic field and the magnetic stirring bar is too strong. Recommendation: Increase rotation speed, reduce power, use smaller magnetic stirring bar.
• If the stirring action is too weak, increase power or use a longer magnetic stirring bar, or stirring vessel of smaller diameter.
• If rotation of the magnetic stirring bar is always irregular, this may be due to temperature or mechanical stress, then a replacement might be required.

Time for a New Magnetic Stirrer? Questions to Ask When Buying a Magnetic Stirrer

If you’re in the market for a new magnetic stirrer, you have a good amount of great options to choose from. Be sure to take your time and select the right model that fits your needs, budget, laboratory applications, and consider the following questions.

Questions to Ask When Buying a Magnetic Stirrer

Shop High-Quality Magnetic Stirrers at Pipette.com

Looking to save time and boost productivity in your lab? Start by adding essential mixing equipment to your operations! For high-quality options at prices you can’t find anywhere else, explore Pipette.com.

We’re the friendly lab supply company that you can depend on for reliable service and care at every turn. Our price match guarantee ensures you’ll never find a better deal. 

Shop our selection of magnetic stirrers, vortexes, and other liquid-handling essentials today.