But in general, nearly every stirring application includes a complex aspect or two, says Jim Jacso, director of sales and marketing at Glas-Col in Terre Haute, Indiana. “There is always something tricky in trying to get information about what the customer is really doing or really wanting to do,” Jacso says.
Given the vast variety of stirring applications, Oliver Vogelsang, product manager for stirrers at IKA Werke in Staufen, Germany, says, “It is important to choose the most suitable test conditions—stirrer performance, geometry of the stirring element, vessel type and geometry, rpm, temperature, etc.—in order to achieve the optimal mixing result.”
To select the best stirring technology for a specific application, Vogelsang recommends defining the conditions. This includes knowing the sample volume and viscosity, the required rpm, and whether it needs vacuum. Some stirring applications must also measure characteristics of the sample, such as temperature, pH, or change in viscosity. The systems might also need to adjust to changes that develop during stirring. “When the viscosity changes as you run a reaction,” says Jim Dawson, president of Heidolph North America in Elk Grove Village, Illinois, “you need to keep the stirring speed the same. So you need a system that will adapt to that.”
In addition to understanding how the stirring must be performed, users should also consider what technological features would come in handy. Maybe it’s as simple as needing a stirring device with a display of all the functions. Many scientists want a computer connection, such as a USB or RS-232 port, programmable functions, and a remote control. As Jacso points out, “Computer interfacing is becoming more prevalent.”
Accuracy or else
One researcher, who preferred not to be mentioned by name, used specific forms of stirring in a process that makes large amounts of oligonucleotides. Asked how crucial stirring rpm and temperature control are to his work, the researcher replied, “Absolutely critical.”
In addition, this scientist would like some specific features in stirring technology. For one thing, he expressed an interest in “speed control with motor feedback.” Moreover, he says, “It would be great also to have cooling capacity rather than the standard heating.” Then, he added, “Saying that, such a model may exist, but I have never really searched for it.”
Some of the most complex stirring applications arise in a pilot project that must eventually be scaled up. “So we need to know someone’s long-term plan even from the start,” says Jacso, “especially when a process will need scaling up later.”
In those cases, the vendor must be mindful of the necessary speed and torque, particularly as the sample size increases. “There’s lots to think about,” Jacso says, “like the horsepower you’ll need.” The specific application also impacts how complex scale-up can get. The more viscous the sample, the more complex the potential scale-up problems. As Dawson says, “As you scale up, data capture helps you quantify and understand all of the characteristics.”
So when it comes to what you need in a stirrer for a demanding application, do make a search for all available options. The technology might have advanced in ways that you haven’t realized.
For additional resources on stirrers, including useful articles and a list of manufacturers, visit www.labmanager.com/stirrers
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