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Product Focus: Stirrers

Controlling the environment and the operation determines much of the accuracy

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A glass rod swirled in a beaker worked fine for laboratory stirring for years, decades, and more, but that won’t do today in most cases. As Oliver Vogelsang, product manager for stirrers at IKA in Staufen, Germany, explains, “Stirrers are being more and more integrated into automated processes.” Such advanced uses of stirrers require updated technology. In addition, stirring in general often depends on far more sophisticated features than rhythmic hand power.

Some of the technological needs arise from using stirrers in so many ways. “Stirrers are used in very diverse lab settings, from beakers and round-bottom boiling flasks to 200-liter pilot project reactors,” says Jim Jacso, director of sales and engineering at Glas-Col in Terre Haute, IN. “Mixing is a key to lots of work done in research as well as in production environments.” As examples, he points out bacterial resuspension, polymer research, and larger systems that need multiple paddles to keep everything thoroughly mixed. Even these disparate examples, though, provide only a glimpse into the overall application space for stirrers.

Turning up the technology

One key element to stirring comes from the motor. Joseph Novotny, senior engineer at Eberbach Labtools in Ann Arbor, MI, says, “There is a shift by many manufacturers, including us, from brush-DC motors to the brushless style, which provides an advantage in size and torque.”

The technology inside a stirrer must not only mix a sample but also do so in a specific way. That often requires a specific motor and paddle combination. A stirrer must even keep track of changes in what it is mixing. As Vogelsang says, “Another important factor is the measurability of changes in the fluidity of the probe, which is provided by a torque-trend measurement.”

Tracking this characteristic of a sample, its viscosity, is common enough that other experts also mention it. For example, Jacso says, “Lots of people want to know when viscosity is changing in their samples, and getting that data requires monitoring the current draw of the motor and then interpolating that into the data that the user needs.” With this capability in a stirrer, a researcher can keep track of changes in a sample over time.

Beyond information on a sample’s viscosity, users want other data. Consequently, says Jacso, “People like nice user interfaces as well as being able to connect the output of a stirrer to a PC so they can gather data.” He adds, “They want to make sure that the device is doing what they want and that it provides information on what they’re researching.”

Going the distance

In some experiments, a researcher wants some distance between the control of an experiment and the actual process. “The newest technology,” says Vogelsang, “allows for the control element to be removed from the stirrer. This feature enables tests to be controlled through the protective cover of an extractor hood.” He adds, “One of the benefits is increased user safety.”

That separation can also improve performance. As Jacso says, “The key is to try to keep the stirrer’s control away from solvents as much as possible, but that’s kind of hard because the motor and control are often in one package. Vapors can get inside and impact the electronics in the controls.” He adds, “We keep the motor and controls separated.”

Beyond providing control across a physical distance, a good stirrer should last a long time. Vogelsang says, “Stirrers are very robust, and they generally withstand the demanding laboratory routine.” To ensure that long performance, though, he reminds users that it is important that the “devices are handled with care” but “if all directions in the manual are followed, the stirrers will enjoy a very long life.” To make sure that the directions get followed, Vogelsang says, “It is mandatory that a laboratory manager properly trains the staff in handling the lab devices.”

Stirrer selection

Getting the right stirrer depends completely on how it will be used. As Vogelsang says, “Any new stirrer would have to fulfill the requirements of the application. That could be a high-torque or -rpm range, a USB interface, a timer, a reverse-rotation function, and much more.” When shopping for a new stirrer, Vogelsang says, “It’s better to have too many functions than not enough.”

Many users hope to put stirrers to use in various ways. For example, Susan Campbell, associate professor of biochemistry at Georgetown College in Kentucky, says, “We use stirrers during titrations and some enzymatically catalyzed reactions and, of course, making simple solutions.” In terms of function, she says, “The stirrer needs to operate smoothly at multiple speeds with different-sized stir bars—from ‘fleas’ to much larger bars.” So she needs a stirrer that provides a range of stir bar options.

In many cases, though, a user can’t get everything in a single stirrer. As Jacso explains, “Everybody is always looking for high speed and high torque, and often they have to sacrifice one for the other. You can’t have both worlds.”

Sometimes, though, simple is enough. As Novotny says, “The majority of people just want to dissolve something. In those cases, a simple stirrer with analog controls works just fine. I’ve used that kind of stirrer to mix many batches of photographic developer and stop bath and fixative—yes, in the old days of film photography.”

Ultimately, though, a customer needs a stirrer that meets the needs of the lab. If you need more stirring control or power, keep that in mind. “Some people buy cheaper systems, and they won’t work,” says Jacso. “They burn up in the labs if, say, the mixing viscosity is too high.” He adds, “Higher-quality stirrers tend to keep users satisfied.” Only you know just what you need.

For additional resources on stirrers, including useful articles and a list of manufacturers, visit