Cleaning a cryoprobe

One of the Skaggs NMRs is normally fitted with a 1.7mm cryoprobe. This piece of equipment is essential for our natural products and metabolomics users who have limited amounts of their samples. The capillary sample tubes for the 1.7mm cryoprobe use special shuttles that do not grip the tube. If the probe gets dirty then the tube can fail to enter the top of the probe and instead gets pushed up out of the shuttle. This becomes apparent when the sample fails to produce a lock signal. Repeatedly ejecting and inserting the sample tube can sometimes get the tube to drop into place by luck, but this is not really a viable solution. If the 1.7mm tubes are not entering the probe reliably then the probe needs to be cleaned.

The Bruker cryoprobe user manual provides the following instructions on cleaning cryoprobes.

Cleaning the sample cavity

The CryoProbe sample cavity is extremely fragile. Even a tiny scratch inside can spoil the CryoProbe performance and entail a major repair action. Preventive cleaning is not recommended - clean only in case or problems.

CAUTION: Do not put any objects or cleaning devices into the sample cavity! in particular, soft cotton buds must not be introduced under any circumstances - the CryoProbe cavity would almost certainly be damaged!

If dirt or liquid must be removed from the sample cavity, follow the procedure given in Table 6.4 below.

Table 6.4. Clean the CryoProbe sample cavity

step	action
k.1	Remove the cryoprobe from the magnet and observe all handling precautions.
k.2	Put the Cryoprobe upside down onto the edge of a level surface, e.g. a table, such that it cannot fall down. Its tube must point down but without touching anything.
k.3	Protect your eyes with goggles.
k.4	Connect the VT gas to its regular input at the Cryoprobe bottom and select a flow rate ≥ 1000 l/h in edte.
k.5	If some debris or liquid is trapped inside the sample cavity, flush it out with jets of (1st) water and (2nd) alcohol. Use a syringe or a wash-bottle which you direct from below in to the sample cavity. CAUTION: Do not immerse in alcohol for an extended period of time. Do not use solvents other than those listed above! Take extreme care not to touch the inside of the cavity. Do not flush anything but VT gas through the VT gas channel inside the CryoProbe. Do not reverse the direction of VT gas flow.
k.6	Wait until the VT gas stream has dried the entire cavity
k.7	Set the VT gas flow rate back to its previous value and detach the VT gas hose from the CryoProbe.

If this procedure does not solve the problem contact BRUKER.

The protocol above is useful if a tube has broken in the probe, but in our case the cryoprobe normally has a buildup of dirt and oil transferred from fingers when handling the tubes. To remove this buildup a Bruker engineer recommended the following protocol.

1. Warm up the probe and remove it from the magnet.
2. Place the probe on a flat level surface with the opening for the sample tubes facing downwards, e.g. the cryoplatform.
3. Beneath the cryoprobe tube place a 600ml beaker on a stir plate and a lab jack.
4. Add 200ml of methanol and a magnetic stir bar to the beaker.
5. Using the lab jack lift the beaker up so that the first 5cm of the cryoprobe tube is covered with methanol.
6. Using the stir bar agitate the methanol to wash the probe for 15 minutes.
7. Remove the probe from the methanol and place in a stable position where it can be connected to the VT gas, e.g. cryoprobe case.
8. Connect the VT gas, set the flow rate to 1000 l/h using edte and dry for an hour.
9. Reinstall the probe and cool down.

I have successfully used this protocol several times to restore the ability to get a lock signal. Ultimately though, the best solution is to prevent the probe from getting dirty. All sample tubes should be cleaned with Kimwipes before being placed in the magnet.

Acknowledgments

Thanks to Joshua Schweer from the Siegel lab for providing all the lab equipment.