The Department of Chemistry and Biochemistry
The Michael Faraday Laboratories
Northern Illinois University
DeKalb, IL 60115-2862
Using the Temperature Control
Both NMR instruments are equipped with heating and cooling units. When using the 500 MHz instrument, cooling can be achieved using either the BCU 05 (down to 20 degrees below ambient, i.e. about 5 deg. C) or a liquid nitrogen evaporator. The 300 MHz is equipped with a liquid nitrogen evaporator.
To run the instruments at constant temperature, set up the desired experiments as usual.
- Type edte into the command line, the temperature controller will be initialized and the edte window will open.
- Under target temperature à press change and enter the desired temperature into the field, o.k. The target temperature is measured close to the sample tube, i.e. corresponds to the desired sample temperature.
The heater and cooling unit work together to reach and stabilize a desired temperature. Always turn on both units together. If you need temperatures higher then ambient, set the heater power higher than the cooling. If you need lower temperatures, decrease the heater power and increase the % cooling.
Make sure you know the temperature limits of the different probes (check the website under NMR instrumentation) – probes are only to be used within these temperature limits to avoid damage! Also, make sure that you know the boiling or freezing point of the solvent in use. If your solvent freezes, the lock will be lost and NMR spectra cannot be obtained. Boiling solvent in the tube will eventually cause overpressure and the tube will burst inside the probe.
- To activate the heater, push the set max button under heater and set the heater power. Start with a low heater power of ~ 10%. Never set the heater power to 100% !!! Exit the menu and turn the heater on by clicking the off button. On the 500 MHz the BCU05 is linked to the heater. When the heater is turned on the BCU05 will turn on automatically. If you don't want this, you will have to switch it off manually on the box.
- For cooling: On the 500 MHz the BCU 05 can be used for temperatures down to about 5 deg C. You will not see the BCU 05 in the edte window, but you can hear it turn on when the heater is turned on. If using the liquid nitrogen evaporator, fill the dewar with liquid nitrogen, insert the fill tube and close the dewar with the provided hardware. One side of the fill tube will replace the green air line at the bottom of the probe. Clamp the connector in place for a good seal. Be careful not to damage the glass joint.
The evaporator is connected to the temperature controller and can be regulated in the edte window.
Under cooling, click on change to choose a cooling percentage (start low and then increase if necessary). Then turn the evaporator on by clicking the off button (make sure that the BCU05 is turned off).
- Under data à monitor temperature & output power, a graphical window opens which can be used to follow the temperature development.
- Once the experiment is completed, set the target temperature to ambient and wait for heater and cooling unit to reach this temperature. You might have to change the heater power and cooling %. Only turn off the heater and cooling unit once RT is reached.
Tips and Troubleshooting:
- Increase or decrease the temperature slowly in order to avoid putting too much strain on the instrumentation (the probe and the shimstack). Do not change it more than 10 deg in about 10 minutes.
- If your temperature only changes to a certain degree but does not reach the desired temperature for the experiment, change the heater power and cooling %.
- The liquid nitrogen dewar lasts a long time, but if you are planning overnight experiments, make sure you have enough liquid nitrogen in the dewar.
- Preferably, experiments using temperature control should not be left unsupervised for longer periods of time.