Xcell: frequently asked questions
How much time do I have to get the pressurised crystal from the Chamber to the cold stream before the xenon is lost from its respective sites?
The time needed to get the sample from the Chamber to the cold stream depends on the macromolecule being looked at. In many cases, there is more concern with the sample drying out than losing xenon from the structure. So the conclusion seems to be anything from 2-10 secs or more!
What fittings and accessories does the Xcell come with?
The Oxford Xcell is supplied with all the appropriate connectors, the gas transfer line from the cylinder which is fitted with a 1/4" OD tube for a compression fitting to fit into a regulator and a box of filter papers to soak in mother liquor to keep the Chamber moist. There is also the option to purchase a hand pump.
The Oxford Xcell is NOT supplied wih a gas regulator.
What sort of regulator do I need for the xenon cylinder?
It is a good idea to purchase a rare gas regulator locally. The reason for this is that xenon cylinder regulator thread can vary so the one supplied by Oxford Cryosystems may not fit any xenon cylinder. You must get one that:
- Is single staged.
- Has a maximum output pressure of 25 bar.
- Is suitable for rare gases.
Regulators can be purchased from most gas suppliers such as BOC, Air Products or specialist rare gas suppliers such as Spectra Gases or Green Gases (www.green-gases.com).
What size xenon cylinder should I buy?
The size of xenon cylinder you purchase is up to you. The most important thing is the pressure in the cylinder. The Xcell is regulated up to 25 bar. If you get a full 35 bar cylinder, although it will be expensive, you get far more gas out of it. There is the option of buying the hand pump for pumping the Xenon into the Xcell when the pressure in the tank gets too low. Xenon can be purchased from most gas suppliers such as BOC, Air Products or specialist rare gas suppliers such as Spectra Gases.
Can the Xcell be used with other gases including krypton at higher pressures?
Important - never use oxygen with the Xcell.
The Xcell can be used with gases other than xenon. However, it is worth noting some general precautions first. Consult the local Safety Officer before dealing with high pressure gases or any kind. Some explosive gases, such as Hydrogen, can cause sparks when vented along gas paths so either vent slowly and in an anaerobic enclosure. Be sure not to exceed the maximum pre-set pressure of 25 bar. Purge the Xcell with a gas such as air or nitrogen once the experiment has finished. Repeat the purging many times, as gases can be retained in the Pressure Gauge. The Xcell has been tested to 55 bar. However, a couple of factory modifications would need to be made before the Xcell could be used at these pressures. Please bear in mind that the critical pressure of xenon is about 60 bar and the critical pressure of krypton is 55 bar.
