Temperature Verification in Lab Stirring

How to Verify Lab Stirring Temperatures

Temperature specifications are critical when laboratory researchers are developing new processes to produce most anything where temperature plays a role in achieving the desired results.  While this may seem a no-brainer the point we wish to make is that first, establishing then second, verifying temperature on an ongoing basis can present challenges.

An example of temperature verification on the domestic scale is found in recommended cooking temperatures in the kitchen.  Fish, meat and poultry products are often packaged with instructions to cook, broil or roast until the internal temperature reaches X⁰F.  Oven temperatures can be set at this temperature, oven thermostats help control the temperature, but what is the internal temperature of the food?    Widely available temperature probes can be inserted in the food either from the beginning or periodically during the cooking to give a close approximation of the internal temperature.

“Close” may be OK when cooking the holiday turkey but does not apply when it comes to developing laboratory processes to be scaled up to commercial production.

Interestingly enough, however, is the fact that laboratory-developed and refined processes emulate those found in the kitchen.  The difference is the degree of accuracy and precision required and achieved.

Temperature Control and Verification for Hotplate Magnetic Stirrers  

Hotplate magnetic stirrers such as the M and KM Magnetic Stirrer series available from CAT Scientific for flat and round-bottom  flasks enable lab personnel to control the speed of stirring (accomplished by a magnetic stir bar also called a “flea” in the flask)  and the temperature of the process.  CAT hotplate magnet stirrers are capable of heating samples to temperatures above 400⁰C in 1⁰C increments and holding set temperature to within ±1⁰C operating from the control panel.  Operators see both the set and actual temperature. Our post on how magnetic stirrers work provides more detail.

But to continue our turkey-roasting analogy, temperatures displayed on the hotplate magnetic stirrer are those of the hotplate, not the sample.  Here temperature probes again come into play but in this case are far more sophisticated than models used on the home front.

Enter the CAT Pt100 Temperature Probe

The Pt100 temperature probe is the answer to hotplate magnetic stirrer temperature measurement and control accuracy.  This is used somewhat like the meat thermometer but is suspended in the sample rather than inserted in the turkey.

(By way of explanation  Pt stands for platinum, a precious metal the properties of which enable accurate determination of the temperature.   In fact, they are more accurate than widely used thermocouples, which is why we offer them at CAT Scientific.)

But unlike the meat thermometer the Pt100 probe is equipped to take control of the magnetic stirrer itself, monitoring the temperature, recording it for record keeping, and initiating shut-down procedures in the event of a magnetic stirrer malfunction or sample loss due to leakage or evaporation.    Moreover, when equipped with a probe the hotplate magnetic stirrer can control temperatures to ±0.04⁰C — a far tighter specification than ±1⁰C and, more significantly, it records content temperature rather than the temperature of the hotplate.

This probe is attached by a clamp and support rod.  The tip is suspended at least 2 cm in the sample but not far enough to interfere with the rotating magnet.  Its wire is plugged into the back of the magnetic mixer making the probe the controller.

For more on this topic see our article on using Pt100 temperature probes or ask us a question on temperature control or other information on our line of scientific equipment.