Many organometallic compounds, catalysts, and reactive intermediates are rapidly destroyed by oxygen or water vapor. The Schlenk line (also called a vacuum/inert gas manifold) provides the controlled atmosphere needed to handle these materials.

The Schlenk Line

A Schlenk line consists of two glass manifolds connected by valves:

• Vacuum manifold: connected to a vacuum pump (typically <0.1 mmHg) via a cold trap (liquid nitrogen or dry ice/acetone) that condenses volatile solvents and prevents pump oil contamination.
• Inert gas manifold: connected to an argon or nitrogen source. A bubbler on the outlet prevents back-diffusion of air and provides a visual indicator of gas flow.

Dual-oblique stopcocks or Teflon valves connect each port to either vacuum or inert gas. The user switches between vacuum and inert gas to evacuate and backfill glassware.

Basic Operations

Flame-drying: glassware is heated under vacuum using a propane or butane torch to remove adsorbed water. After flames have passed over all surfaces, the glassware is allowed to cool under vacuum, then backfilled with inert gas.

Solvent degassing: solvents are degassed by freeze-pump-thaw cycles (freeze in liquid N₂, evacuate, thaw, repeat) or by sparging with inert gas for 20–30 minutes.

Syringe and cannula transfer: liquids are transferred between Schlenk flasks using a double-tipped cannula (a long, flexible needle) under positive inert gas pressure. The source flask is pressurized with inert gas, and the receiving flask is vented through a bubbler. The cannula pierces both septa, and the liquid flows through.

Filtration under inert gas: a Schlenk frit (a glass filter with a sintered glass disc) allows filtration without exposing the solid to air. The filtrate is collected in a Schlenk flask attached below the frit.

The Glove Box

A glove box (inert atmosphere dry box) provides a sealed, recirculating atmosphere with O₂ and H₂O levels below 1 ppm. It is used for weighing air-sensitive solids, preparing NMR samples of air-sensitive compounds, and assembling reactions that require fine manipulation.

The atmosphere is recirculated through purification columns (copper catalyst for oxygen removal, molecular sieves for water). Gloves (neoprene or butyl rubber) are attached to ports on the box face. An antechamber (load lock) allows transferring materials in and out without compromising the box atmosphere.

Safety

• Vacuum work with glass carries an implosion risk. Use tape (electrical tape or laboratory tape) to create a cross-hatch pattern on Dewar flasks and vacuum flasks.
• Liquid nitrogen cold traps can condense liquid oxygen (pale blue) if large amounts of air leak into the system. Liquid oxygen is explosive in contact with organic materials. Always check that the system is leak-free before applying vacuum.
• Regularly check and change the vacuum pump oil. Contaminated oil reduces vacuum quality and can damage the pump.