Magnetic Stirrer: The Silent Lab Machine

Magnetic Stirrer: The Silent Lab Machine Working Harder Than You Give It Credit

A small machine that keeps whirling around a little bar in a beaker non-stop without touching any wires into the liquid is probably a common sight in all labs specializing in chemistry and microbiology. While being considerably less exciting than other lab machines, the magnetic stirrer is definitely a tool whose importance should not be underestimated. Ask any researcher to stop using it and you will not receive an answer that you might expect.

How Does a Magnetic Stirrer Work?

The main operating principle of a magnetic stirrer is that of magnetic coupling. A small rotating magnet is placed within the body of the machine in analogue models. In digital magnetic stirrers, there is an electromagnet producing a rotating magnetic field that passes through the walls of the container and causes the submerged stir bar to spin. There is no direct contact with the solution whatsoever.

That is precisely the reason why modern laboratories choose magnetic stirrers in favor of the mechanical ones. Since there is practically nothing that can touch the sample itself, contamination is ruled out, cleaning becomes effortless because of the small size of stir bars, which makes sterilizing easy. Additionally, the machines run quite silently.

Types of Magnetic Stirrers to Take Into Account

Manufacturers have managed to come up with a few varieties that can fit different laboratories. Analogue magnetic stirrers provide speed control that is enough for normal mixing operations. In contrast, digital magnetic stirrers allow getting accurate data about rotations per minute and temperature, which is needed when performing precision experiments. Those experiments that require simultaneous heating can be done using the magnetic stirrer with a hot plate. This combination is widely used during titration, cell culturing and organic chemistry synthesis. Multi-position magnetic stirrers can be found in use in laboratories working with several samples at once.

Where Stirring Speed Really Matters

Rotation rate is usually counted in RPM. The denser or more viscous the liquid is, the faster it needs to rotate to keep the vortex stable. In case the sample is delicate or contains small amount of fluid, it will require less stirring speed in order to prevent splashing and slipping off of the bar. Nowdays, the best digital units can set speed from about 300 to 1500 RPM, which is much more convenient than using analogue dials of the previous generation.

Where This Tool Fails

As no tool is universal, this one is limited in several situations too. For example, highly viscous liquid is difficult to stir since the stir bar may get out of contact with the magnet and start spinning. Besides, for large volumes of liquids or dense industrial samples, other types of stirrers – overhead ones – are used instead.

Bottom Line

There is no mystery in popularity of the magnetic stirrer in the laboratory since it doesn't require any specific efforts, skills or complex maintenance. No matter whether you have a classic analogue or advanced digital model with a hot plate, it will do the task it was designed for – and do it silently, without making trouble.

Bionics Scientific Technologies is a leading laboratory and scientific equipment manufacturer based in India