linebreak

Variable Temperature (VT) NMR

Bruker Avance Series Spectrometers (0 - 130 °C)
last updated YB 11/10/2010

This document is NOT a substitute for proper instruction.
To make an appointment for proper training, call Shifi or Yael at 3748 or 4919.

Limitations due to the shim system / magnet:
Maximium shim system temperatuer: +80 °C
Magnet flange / bore temperature: 0 to +50 °C

  1. Check-list:
    1. Use a ceramic (heavy, white) or a PEEK (beige) spinner!
    2. Do NOT use a blue spinner
    3. Know the freezing and boiling points of your solution (solvent)
    4. Do NOT use nominal temperatures to calculate entropy;
      accuracy requires calibration
    5. Reserve enough time to completely return the system to room temperature BEFORE you turn is up.
    6. Is the air flow gas connected to the probe?
      (large, grey, insulated arm)
    7. Is the thermocouple connected to the probe? (blue cable)
    8. Is the heater connected to the probe? (white cable)

  2. Highly recommended:
    Start with a room temperature spectrum (lock, shim, acquire) to check that there are no sample or spectrometer suprises BEFORE you begin heating.

  3. Cooling only:
    Switch on the refrigeration unit (single orange switch).

  4. For all VT work: edit temperature
    1. Open the temperature controller (either right-click on the VTU display or type: edte)
      edte display
    2. Sample temp. is the nominal temperature (the temperature measured by the thermocouple; it is not an accurate value for the sample temperature
    3. Target temp. is the desired temperature. Increase the temperature in steps of ~10 °. Check the calibration curve for the probe to be sure your sample stays in the liquid-phase.
    4. Probe heater can be dangerous to the sample, the probe, the shim stack or the magnet!! IF the heater is off, check that the set max setting is less than 3 AND that the gas flow is at least 535 l/hr BEFORE turning the heater on.
    5. Gas flow is extremely important to prevent uncontrolled local heating and damage. The number is the amount of air used to carry the heat created by the heater to the thermocouple (for the feedback loop control) and to the sample.
      If the gas flow is too weak, it will create a severe temperature gradient within the sample leading to poorer quality spectra and potential danger depending on the boiling and freezing points of the solvent. There is also potential damage to the probe and to the magnet system due to unregulated heating $$$$.
      If the gas flow is too strong, more heater current will be needed to warm the extra room temperature air flowing in.

      Heating: minimum, recommended values for gas flow:

      Gas flow (l/h) % heater
      270 no heater
      400 1-2
      535 3-5
      670 6-7
      800 8-9
      935 10
      1070 11
      1200 12
      1335 13


      Cooling: The air entering the probe is cold (~273K) because the refrigeration unit is ON.
      The heater is used to warm the cold air to the desired cool temperature (~ 0 - 25 °C).
      The greater the gas flow, the more cold air, the greater the cooling. Use minimum heating for temperature stability/control - you still must use sufficient gas flow for the percent heating you apply in order to avoid damage to the probe, the shim stack and the magnet.
    6. Allow time for the heater and sample to equilibrate at the new temperature.

  5. Safety and limits
    1. Use sufficient gas flow to avoid damaging the probe.
    2. With low temperature samples avoid water condensation on the tube (water and electricity do NOT mix).
    3. You may heat up to 55 °C for up to 48 consecutive hours.
    4. You may heat up to 90 °C for up to 12 consecutive hours. Allow the system to cool a few hours at room temperature before continuing at high temperatures.
    5. If you heat at the maximum range 100-140 °C, try to limit runs to < 6 hours. Allow the system a few hours at room temperature before continuing at high temperatures to make sure that the bore temperature of the magnet NEVER exceeds +50 °C.

  6. Returning a hot system to room temperature
    1. Reduce the target temperature to 298 K.
    2. Set the heater maximum to 1%
    3. After it has reached room temperature, reduce the gas flow to:
      AV-500: 400 l/hr with the heater on.
      AV-300: 270 l/hr AND turn OFF the heater.
    4. Remove your sample and return the spinner to its padded box for safe keeping.

    Returning a cold system to room temperature
    1. Turn off the refrigeration unit and wait ten minutes.
    2. Increase the target temperature to 298 K.
    3. Set the heater maximum to 1%
    4. Adjust the gas flow to:
      AV-500: 400 l/hr with the heater on.
      AV-300: 270 l/hr AND turn OFF the heater.
    5. Remove your sample and return the spinner to its padded box for safe keeping.