Flash-freezing a sample in liquid nitrogen and storage

• Established a ‘standard’ pin length that will keep the crystal in the centre when it is rotated on the arc during retrieval, or alternatively, fit into your tongs if using this method
• Ensure that all your pins and top hats conform to the standard length
• Label a cryovial. Fill a 2 litre intermediate Dewar with liquid nitrogen and label a cryocane. Fill a glass sample handling Dewar with liquid nitrogen
• Place the labelled vial in the vial holder (or the vial tweezers) and place them both into the glass sample handling Dewar
• Place the small Dewar as close to the microscope as possible
• Hold the top hat on the magnetic wand
• Fish the crystal and plunge it immediately into the liquid nitrogen. The shorter the time the crystal is travelling through the air and dehydrating, the better
• Wait until the liquid nitrogen surface is still. Bring the vial holder and vial up underneath the pin and the top hat. Locate the top hat into the top of the vial
• Move the wand SIDEWAYS to break the magnetic hold between the top hat and wand
• As soon as the top hat and sample are inside the frozen vial, return the vial holder and vial to the glass sample handling Dewar so that the vial and sample are fully submerged in liquid nitrogen
• It is important to note that if a lid is to be placed on the vial, a blowhole should be drilled in the lid before it is used. It is recommended that the lid is placed on the vial if canes with lateral extrusions (to rest the vial base on) are to be used
• Next, bring the vial holder up so that the top of the vial just breaks the surface of the liquid nitrogen
• Put the lid on the end of the lid opener and screw the lid on the vial. Do NOT screw the lid on too tightly as vial lids sometimes freeze on and can be very hard to get off
• Immerse the whole vial and lid in the liquid nitrogen until the surface of the liquid nitrogen goes flat and equilibrium is reached. Lift the vial holder and vial from the glass sample handling Dewar and remove the vial
• Put the vial holder down. With the free hand lift the pre-labelled cryocane out of the 2 litre intermediate Dewar and place the vial on it at the next free position, working from the bottom of the cryocane, upwards
• Make a note of the crystal shape, the marking on the vial and cane and the date. When the canes are full, transfer them to the main storage Dewar all at the same time.
  This avoids opening and closing the storage Dewar unnecessarily, preventing ingress of moisture from the air.
  

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