Cannula transfer

They give an airtight seal, preventing the ingress of the atmosphere, but are able to be pierced by sharp needles or cannulae.

Other workers recommend deeply scoring the cannula with a triangular file, then sharply snapping the weakened section.

While the material is relatively solvent-resistant, although they are designed primarily for aqueous solutions, some degradation or leaching by the contents may occur.

Luer fittings are preferred, as needles are locked in even under higher pressure, e.g. when transferring viscous liquids.

[3] Cannulae and needles should be quickly flushed out with an appropriate solvent to prevent undetectable corrosion damage to the stainless steel.

The vents need to be isolated by capping the bubbler outlet, or stopping the egress of inert gas with a stopcock or pinch clamp, to ensure sufficient pressure to complete the transfer.

By carefully filling the cannula fully with either above techniques, then allowing the pressures within the vessels to equalize, a syphon may be set up.

While handling pyrophoric material (e.g. tert-butyllithium and trimethylaluminum), traces of the compound at the tip of the needle or cannula may ignite, and cause a clog.

Some workers prefer to contain the tip of the needle or cannula in a short glass tube flushed with an inert gas, and sealed via two septa.

Also, there is a reduced tendency for the needle tip to clog due to the reaction of traces of the reagent with air to give salts.

Air-sensitive cannulas: 1: Pressure in (gas in) 2: Pressure out (oil bubbler orange) 3: Higher flask with transfer liquid (yellow) to transfer 4: Lower receiving flask/transferred liquid (yellow) 5: Liquid transfer cannula 6: Septum (orange) on transfer flask 7: Septum (orange) on receiving flask 8: Pressure-control regulator/stopcock 9: Tubing/ gas-line (not shown for clarity, arrows show connectivity) 10: Gas cannula 11: 2-way syringe stopcock 12: Gas-tight syringe 13: Gas/pressure removed from flask 4 14: Gas/pressure added to flask 3 O = Open stopcock; X = Closed stopcock; black-arrow = Gas flow direction, orange arrow = Liquid flow direction