Avance 600 and 800 Cryoprobes

Irreversible damage to the cryoprobe can occur if


Note: due to a bug in Topspin1.3, gas flow and heater can be shown to be off, although it's all fine. In this case, quit and restart Topspin.

The VT unit would also be off after a power failure!

Always set at least 670 litres/hour gas flow on the VT unit (i.e. in edte)!
800 litres/hour is also possible without spinning.

Never allow more than 15% heater power in edte!

Always clean the outer surface of the NMR sample tube after inserting it into the spinner AND before using it in the cryoprobe.

The maximum pulse lengths allowed at high power are (note: powercheck prevents access to these limiting values for 1H and 15N):

Hard 13C and 15N pulses must never be applied simultaneously at full power! (Attenuate the pulses by 3 dB each and it's OK.) Attenuation is also required, if broadband decoupling is applied on one channel (15N or 13C) while a hard pulse is applied on the other (13C or 15N).


z-gradients, combined gradient power per FID: < 10 ms at 100%. At half the gradient strength, a 4 times longer total gradient duration is permissible.

If set up with the prosol command, the standard Bruker pulse sequences and parameter sets are safe, with one exception: in hsqc2etf3gpsi (15N-T2 measurement with CPMG sequence), d20 must be < 250 ms, p30 > 160 μs and d21 > 450 μs.


Suggestions for best results:

Check that the cryoprobe is cold and happy before applying the first pulse:

The desktop icon "cryo_laptop" opens a VNC connection to the cryoprobe laptop. "cryovnc" opens the window for viewing. Make sure the cryo display is open. A green bar on the right hand side of the 1 h window shows the available cooling reserve: this reserve must never go down to zero, but it is usual to drop a little during broadband decoupling.

Tune and match the cryoprobe before shimming - the ATM unit influences the shim.

(Don't tune and match unless the probe is cold - the ATM unit can break otherwise!)

For stable conditions, wait for 10 min after sample insertion before measurement.

Type p90 in any data set to determine the 90o(1H) pulse length. It's safe and accurate!

A gradient recovery delay (d16) of 100 μs is adequate for most purposes (creates no more than 3o phase change after a 1 ms rectangular 80% gradient).


Sample volume:

The best shims are obtained for samples with 40 mm height (this is different from room temperature probes!)

Shigemi tubes: only ever use round-bottom Shigemi tubes! Never use "Varian-Shigemi tubes" - they cannot be centred because their lower glass segment is too long!

The best filling height for Shigemi tubes is 18 mm. Experience shows that the quality of Shigemi tubes can vary. Good Shigemi tubes can deliver better water suppression than normal tubes.


Temperature:

The allowed temperature range is 0-60 deg. C.

Thanks to Peter Barron for calibrating the temperature display with ethyleneglycol: what you set in edte is what you get.

For measurements above room temperature (about 22 oC), it is recommended to turn off the BCU-05 cooling unit. For improved temperature regulation in the range from 22 °C to 26 °C, the switch on the box near the BCU-05 can be set to "low", if the BCU-05 is turned off. (This will limit the heater current for finer regulation). For all other temperature ranges, the switch should be on "high".
Our default setting is to have the BCU-05 off, and the switch on "high".

For measurements below room temperature, the BCU-05 cooling unit should be on and the switch set to "high".

The PID parameters of the VT unit are fine within a temperature range of +/- 5 degrees, beyond that a self-tune is recommended for best temperature stability.


Shimming:

The cryoprobe only has z gradients. Peter set up gradshim so that 1D gradient shimming via the gradient coil is possible, as well as 3D gradient shimming via the room temperature shim coils.


If the cryoplatform decides to warm up:

Heating due to too much power in the pulse sequence will eventually trigger the cryoplatform to warm up. A warm up will also be triggered if the BCU-05 is turned on and the switch on the box near the BCU-05 is set to "low"   - the limited heater power is insufficient to hold the temperature above 0°C.

An alarm will be shown in the cryo display. If recognized within 10 minutes, the decision for warm up can be reversed by pressing the "cool down" button. After that time, the warm up will be completed. Warm up and cool down each take about 2 h. Cool down can be started first after the warm up has been completed. Each warm up and cool down cycle shortens the lifetime of the system and consumes expensive helium gas.


Improved sensitivity for salty samples

There is now a sample spinner for 3 mm NMR tubes. A 3 mm tube (e.g. Wilmad 335-PP) gives the same filling height with only a third of the volume of a 5 mm tube (e.g. 0.2 ml instead of 0.6 ml).

Bruker data on a 700 MHz cryoprobe show that 100 mM NaCl reduces the sensitivity by more than 50%. At 500 mM NaCl, the sensitivities achieved with 3 mm and 5 mm samples is virtually the same. For an aqueous sample in the complete absence of salt, a 3 mm sample with twice the solute concentration as in a 5 mm sample achieves the same sensitivity.

3 mm tubes break more easily than 5 mm tubes. Therefore, our spinner has a particularly soft insert. Consequently, spinning is not recommended.

Caution! 90 deg. pulse lengths of 3 mm tubes are shorter than for 5 mm tubes. NEVER apply a pulse with a power corresponding to a 90 deg. pulse shorter than 8 us! This means that we must never try to adjust the pulse length with more power than 1 dB! The use of p90 is safe.


Care needed when connecting or disconnecting cables

A warning that has been issued by the Cryoprobe Deparment:

The cold preamplifier and the sensors of the CryoProbe are both subjected to the risk of damage due to electro-static discharge (ESD). Therefore special care is needed when connecting or disconnecting cables to the CryoProbe. Never touch the inner pin of a RF-cable or of a sensor cable while it is connected to the CryoProbe. Always disconnect it first from the CryoProbe before disconnecting it from the HPPR or from the CRCO. And always connect a cable first to the HPPR or to the CRCO before connecting it to the CryoProbe. Never touch the inside of a RF-connector or sensor connector of a CryoProbe.

800 MHz NMR Home