Note: Only trained and authourized users are allowed to conduct VT experiments.

NMR500 is equipped with a FTS temperature control unit and cooler with air supplied through a new Parker/Balston air dryer and pressure regulating tank. The FTS controller sits in the back corner of the room facing the 500 magnet. The FTS should be left on at all times. Do not turn it off unless instructed to do so. Each power-off of the system requires a new 20 mins or longer pull-down of the system to -80C and back up to the set temperature.

The FTS system sends dry, temperature-regulated air (26C)  into the probe so that the sample temperature is ~23C. This setup is a compromise between temperature stability and ease of use for routine work. For temperature ranging from ~ -70C to 90C, the FTS is sufficient for routine VT experiments.

Although the procedure is simple, you are strongly advised to notify me of your plan the first time you do an VT experiment. Please e-mail me with your plan, including time, temperature range and experiments to do. Once you are trained to use the system, you can do the VT experiments in the future by yourself.

Note, the displayed temperature at FTS and in vnmrJ may differ from the actual sample temperature. A few degrees offset is quite normal once the target temperature is 20, 30C off room temperature. If accurate temperature setting is needed, you should calibrate it with an ethylene glycol (for temperature above ambient) or methanol (for low temperature) sample. Please talk to staff for detailed procedure doing this.

Procedure

• Use the brown spinner for VT experiment. The white spinner does not meet specifications required for temperature way off ambient temperature.

When performing VT experiments, closely watch VT display and FTS set temperature and observe all dangerous signs and alarms.

• Check the melting and boiling points of your solvent (see Solvent Table here). Make sure the solvent and your compound will not freeze, boil, or run into other dangerous situations at the temperature desired.
  
• Make sure VT air line is connected to the probe and flow rate on the VT air meter is set to ~15-20 LPM (liter per minute). If not, turn the flow control dial to adjust it. Very low or high temperature may need higher flow rate.

• Two different methods allow temperature regulation:

  • Solely use the FTS control and bypass temperature regulation in vnmrJ altogether. This is sufficient for most routine VT use.
    • Type temp and toggle temperature regulation off
    • Press the Up/Down arrow button on FTS to set temperature. The actual temperature in the sample area should be read from the VT display by the computer. Adjust the FTS set point temperature until desired temperature at the VT display is reached. Setting FTS temperature 10C lower than desired sample temperature should get you close to the desired sample temperature read from the vnmrJ display. Taht is, for sample temperature of -50C, set FTS temperature to -60C.
    • Typically a minimum of 15-20 mins is needed for full temperature equilibration.
      
  • A second method is to engage both the FTS and probe heating for temperature regulation. It may offer better temperature stability. This method only works if desired temperature is -50C or higher because the lowest FTS can reach is ~-70-80C.
    • Set the FTS temperature to ~15-20C below the desired temperature. For example, for 60C sample temperature, set FTS setpoint to 40C.
    • Type temp and turn on VT regulation in vnmrJ. Set desired temperature and wait for VT display to come to target temperature.
    • Normally 15-20 mins are required for full temperature equilibration
• Once the VT operation is done, eject your sample. Set the FTS temperature to 26C. If temp regulation in vnmrJ is turned on, change the target temperature to 23C and turn temperature regulation off. Wait until VT display to show temperature to come to 10-40C before inserting the Idle (cdcl3) sample.

H. Zhou updated Aug 2011