Laboratory Equipment

Magnetic Stir Bars are widely used in chemistry and biology research labs. There is always a need for effective and efficient instruments for stirring liquids. The components of the device will depend on the application.

What is a Magnetic Stir Bar?

A magnetic stir bar is an instrument used in labs that creates a rotating magnetic field. This instrument consists of either a rotating magnet or a stationary electromagnet. A stir bar consists of a magnetic bar that is used to agitate a liquid substance. These stirring bars are covered with glass or Teflon since they do not react with the immersed fluid.

What Does a Magnetic Stir Bar Do?

The magnetic stir bar is placed in the liquid inside a container while another magnet is placed under the container. The magnet underneath the container attracts the magnetic stir bar within the container. The magnet underneath the container is typically attached to a spinning motor. When the two magnets are close enough, it causes the stir bar magnet to spin inside the container.

Magnetic stir bars stir a liquid without having to stick anything down in the container. They can mix liquids in containers that don’t have openings or that are completely sealed. They are instrumental in stirring liquids within containers that are modestly sized. Since there is nothing to stick inside the container, there is no need to worry about leaks or the contamination of the fluid.

How Do I Choose a Magnetic Stir Bar?

Stir bars differ in shape, size, and material. What you choose depends on the application. The form of the stir bar will depend on the vessel and the shape of the bottom of the vessel used for the application.

When choosing the size of the stir bar, there are several factors to consider. These include the volume of fluid, vessel shape & size of the opening, and the size of the internal drive magnet.

For small volumes, you will want a stir bar that is small enough so that it does not touch the sides of the vessel. For large volumes, you’ll want a larger stir bar that will create more motion. The length of the bar should be about the same size as the magnet to avoid spinout and drag.

The magnetic properties and coating will affect which magnetic stir bar you choose as well. With large volumes of liquid, stir bars that contain samarium cobalt create stronger coupling and reduce spinouts. Glass-coated options are necessary for use with highly abrasive materials.

Types of Magnetic Stir Bars

Magnetic stir bars differ in shape, size, and material. Here are the different types of magnetic stir bars:

Round - Round stir bars are commonly used with flat bottom vessels.

Slide round -  Slide round stir bars are designed with a pivot ring around the center and work best with curved or uneven bottomed vessels. The ring reduces vibrations, wear, and the effects of friction.

Spherical -The ball or spherical stir bars are used in small volumes typically found in vials and tubes.

Ellipse - Ellipse or oval-shaped stir bars are designed for mixing in round bottom beakers.

Cross - The cross shape stir bars create additional turbulence good for stirring and are suitable for stirring up sedimentation and at high speeds.

Crosshead - The crosshead or crown is ideal for use in a test tube or cuvette.

Bone - Bone stir bars create a large amount of turbulence at low speeds. They are designed for use in vessels with arched bottoms.

Prism - The prism or triangle creates a lot of turbulence at low speeds and reduces sedimentation due to its shape.

How Do You Store a Magnetic Stir Bar?

There is a protocol for storing magnetic stir bars. Stir bars should not be stored at random. Instead, they should be stored in pairs. Storing in pairs will help maintain magnetic strength. They also should be stored in such a way that prevents them from falling on any hard surface.

Can You Autoclave Magnetic Stir Bars?

Autoclaves operate at high temperatures and pressure to kill microorganisms. Stir bars are designed to resist harsh chemicals and high temperatures. Therefore, you can autoclave magnetic stir bars. 

Where Can I Purchase a Magnetic Stir Bar?

Lab Pro offers a large variety of magnetic stir bar products. For over 40 years, Lab Pro Inc. has been committed to delivering the highest quality chemicals, tweezers, and hard-wire cutters, lab supplies, and cleanroom PPE apparel to medical device and electronic manufacturing companies and laboratories worldwide. To learn more, visit the biggest Lab Supply showroom in California, or contact us online at 888-452-2776.