You probably got the problem solved by now, but I wanted to add a small contribution that may be helpful.

We store (2%) OsO4 solution in water using a glass bottle with tight-seal screw cap that is wrapped in tin foil (quitre heavily) at -80ºC. After years of storing it like this we are pretty confident that no Os leakage is occuring (plus the safety dpt. uses to check our freezers by raman spectroscopy for Os traces and they haven't found any noticeable signal).

However, if those methods are not available to you or are still concerned you can store the Os solutionin the metal can provided with the Os salts as Wolfgang advised and include a PP strip inside the can. We use white PP strips from weighing plates as a passive detector of any leaking occuring while the freezing process is ongoing. It is a cost-effective detector for volatile Os, and a very handy one I must say.

Regards

I do work with OsO4 but with very low quantities. I actually do not know what you do with this mixture but I assume it also contains OsO4. As OsO4 has a boiling point similar to water I cannot assume loss of OsO4 at this temperature and definitely now sublimation. If you had loss you would be able to smell it as the flavor of OsO4 is like garlic (hence the name of Osmium derived from Greek "smell" or so).

A typical procedure is to dissolve the osmium tetroxide in acetone immediately before use, and chill it in a freezer. This is not for long term storage. See the following for an example:

http://www.fgsc.net/neurosporaprotocols/Cryofixation_NC.pdf

Thomas, Richard, thanks a lot for your inputs!

It is quite understandable, that one schould use preferably only freshly made solutions for any of the specimen preparations. But we made a mistake and bought crystalline Osmium packed at 1 g. Now for us it is not very rational to use every week a fresh ampuole to make 25 ml of 4% stock solution and then to discard actually 95% of it... That's why I have started this topic.

I have the experience now (thanks for this advise to Dr. Egorov from MPI Dortmund), that if you use 4% OsO4 in H2O, you may actually batch the excess of it in cryo-tubes, seal it and freeze at -20 °C. In that case everything is fine and Os does not escape and does no harm either to you or to the freezer. Trying to do the same trick with acetone-dissolved Os I failed as acetone remains perfectly liquid at -20°C and Os slowly escapes from the cryotubes, staining black the plastic bottle where I kept it. That's why I have started this topic - how to store the extra ammounts of Os containing acetone that I still could use it and the same time that I do not endanger anyone or the cells or the equipment...

Perhaps your problem has been solved meanwhile.

Just to comment on storage of 4% OsO4 solution in water:

From several references(*) it can be seen that PP-/ cryotubes are not / may not really be the optimal storage container (OsO4 naturally will react with PP as with other plastics).

Also one should understand /should know that OsO4 vapour pressure (volatility) is the critical value instead of perhaps boiling point. This results – even at temperatures of minus 20 to minus 24 degr. C - over longer periods of storage in the refrigerator in progressive blackening of the fridge’s interior, as well as with items put therein for storage (this is a quite normal experience to Electron Microcopists: even 2% OsO4-hydrous solution in a lab-glass bottle with tight PP or similar screw-cap made of (e.g. white) plastic material, additionally wrapped by (3-4 layers) of Parafilm at minus 24 degree-storage will penetrate through the plastic of the screw cap as well as penetrate through the parafilm layers in a time range of say 3-6 days, especially if you unload frozen / melted Osmium solution out from the bottle for two or three times (warming up to RT – unloading – freeze again) So - in the end – you nevertheless might/should be careful storing your specimens/probes in the same storage area you place your PP-tubes or other storage containers with the Osmium. Therefore a storage of small, tightly stoppered (better screw capped glass vials, altogether located in a separate containing device (cardboard box, metal can [as OsO4 crystals will be shipped nowadays] with tightly closing metal lid) can be recommended, if you use only cryovials, storage at least at minus 80 degr. C is advisable.

PS: Perhaps you have seen also the protocol on cf. http://cryoem.nysbc.org/FreezeSubProtoc.html

You unfortunately cannot follow until the end point 11, since you don’t have an extra LN2 dewar for the Osmium-Aceton vials. If needed I can send references off a list to you.

You probably got the problem solved by now, but I wanted to add a small contribution that may be helpful.

We store (2%) OsO4 solution in water using a glass bottle with tight-seal screw cap that is wrapped in tin foil (quitre heavily) at -80ºC. After years of storing it like this we are pretty confident that no Os leakage is occuring (plus the safety dpt. uses to check our freezers by raman spectroscopy for Os traces and they haven't found any noticeable signal).

However, if those methods are not available to you or are still concerned you can store the Os solutionin the metal can provided with the Os salts as Wolfgang advised and include a PP strip inside the can. We use white PP strips from weighing plates as a passive detector of any leaking occuring while the freezing process is ongoing. It is a cost-effective detector for volatile Os, and a very handy one I must say.

Regards