Digital Magnetic Stirrer

Introduction

The digital magnetic stirrer is a device used frequently in labs to agitate liquid mixtures or solutions. It comprises a stationary or rotating magnet that generates a rotating electromagnetic field. The instrument generally consists of a hotplate to contain the sample container and a stir bar. The stir bar is immersed in the liquid to be mixed and is rotated by an electric motor equipped with a magnet. A magnetic stirring system, combined with the heating system, facilitates easy and quick spinning and mixing of the solutions. The digital magnetic stirrer is frequently used in biology and chemistry labs to agitate or homogenize the samples. 

Stirring is performed in laboratories to homogenize the mixtures by accelerating heat and mass exchange in them. Stirring, mixing, or agitation of samples can be performed using various mixing devices like mechanical stirrers, shakers, or magnetic stirrers. Among these techniques, a digital magnetic stirrer is the most familiar device used for the most efficient stirring. The researcher can place a variety of non-magnetic vessels on the horizontal surface of the hotplate. As glass does not affect the magnetic field, glass containers, beakers, vials, etc., are usually used to homogenize the samples using a digital magnetic stirrer. The stirring bar is made chemically inert by coating it with a polymer or glass.   

The magnetic bar of the stirrer is inserted into the liquid and is derived by the electromagnets underneath the hotplate for stirring purposes. These stir bars are made of polytetrafluoroethylene (PFTE) or rarely with glass. These coatings are biocompatible and make the bars chemically inert, so they do not react with the vessel contents. Sometimes, the stir bar has a pivot ring around the core on which they spin. In addition, these bars are octagonal or circular, and a few millimeters or centimeters in size. They can be easily cleaned or sterilized. They contain a heating element having up to a thousand watts of power (Selvaraj et al., 2021). 

Principle

A magnetic stirrer employs a rotating electromagnetic field and vortex for its working. The body of a stirrer encloses an electric motor with a magnet on the top. As the motor moves, it causes the magnet on the top to rotate, thus establishing an electromagnetic field. This rotating electromagnet keeps the magnetic stir bar immersed in the sample container, causing it to move circularly. This circular motion creates a vortex in the container, allowing the solution to agitate and become homogenized.

Apparatus and Equipment

The digital magnetic stirrer comes with a chemically resistant, 16.5 x 16.5cm ceramic hotplate and a magnetic stir bar. Its advanced microprocessor control system allows the user to adjust the spinning speed and temperature easily. In addition, the easy-to-read large LED display makes it even more ideal for use. The samples can be agitated between the speed ranges of 200-1500rpm and heated up to an ambient temperature of 380oC. Conduct Science offers a digital magnetic stirrer with a small footprint and a digital display with increased efficiency and durability.

Applications

Coating archwires with ZrO2 in Orthodontic Treatment

Selvaraj et al. (2021) studied the effectiveness of stainless steel (SS) and nickel-titanium (NiTi) wires coated with zirconium oxide nanoparticles in orthodontic treatment. They used a digital magnetic stirrer with a hotplate to coat orthodontic NiTi and SS wires. The magnetic bar of the stirrer, coated with the inert polytetrafluoroethylene (PFTE), was immersed in the liquid, and another set of electromagnets underneath the hotplate derived the bar’s motion. They examined the surface of each of the retrieved orthodontic arch wires (0.014 NiTi and 19×25 SS) for cracks under an optical microscope at 100X magnification. They placed it in a beaker containing zirconium oxide solution covered with aluminum foil. Then, they placed the beaker on a digital magnetic stirrer and stirred it for 15 days at 450-470oC for the “consistent coating process.” Ultimately, the archwires were coated and the ZrO2 solution vaporized. At this point, they removed the beaker from the stirrer and observed it under a microscope. They concluded that the novel “digital magnetic stirrer method of coating” changed the color of the NiTi and SS archwires from red to orange. 

Hydrolysis of Tapioca Flour’s liquid waste content

Sari et al. (2020) performed bioethanol optimization in the hydrolysis and fermentation with the surface response method. Their study was based on the fact that starch present in the liquid waste of tapioca flour can be converted into glucose by a chemical hydrolysis process with solid NaOH. Then this glucose can be converted into bioethanol by yeast fermentation. The researchers stirred 5L liquid waste of tapioca flour and mixed it with 1-5mg NaOH at 40oC for 15-60 minutes using a digital magnetic stirrer. The results showed that optimum glucose levels (18% v/v) are observed in the hydrolysis process carried with 3mg NaOH and 45 minutes of digital stirring. They concluded that optimum glucose levels are 18% v/v and bioethanol levels are 21.9% v/v in this fermentation process.

Strengths and Limitations

The foremost advantage of digital magnetic stirrers is that they have a chemically inert stir bar that reduces the risk of sample contamination. In addition, the bar can easily be cleaned and sterilized. The digital display and microprocessor control system allows easy temperature and speed adjustment according to experimental parameters. Fluids of different viscosities can be homogenized by using magnetic stirrers. Moreover, these stirrers are noise-free and have minimum vibrations. However, due to their smaller size, these stirrers can handle only small sample volumes of up to 1L and are unsuitable for large-scale samples.

Summary

• The digital magnetic stirrer is a device used frequently in labs to agitate liquid mixtures or solutions.
• The instrument generally consists of a hotplate to contain the sample container and a magnetic stir bar.
• The sample container is placed on the hotplate, and the stir bar is immersed in it.
• A magnetic stirrer employs a rotating electromagnetic field and vortex for its working.
• The magnetic stirring system, combined with the heating system, facilitates easy and quick spinning and mixing of the solutions.
• The digital magnetic stirrer is frequently used in biology and chemistry labs to agitate or homogenize the samples.

References

 Sari, N. K., & Purbasari, I. Y. (2020, October). Bioethanol Optimization in Hydrolysis and Fermentation Process with Surface Response Method. In 2020 6th Information Technology International Seminar (ITIS) (pp. 297-300). IEEE.

Selvaraj, A., George, A. M., & Rajeshkumar, S. (2021). Efficacy of zirconium oxide nanoparticles coated on stainless steel and nickel-titanium wires in orthodontic treatment. Bioinformation, 17(8), 760.