Understanding when and why to use certain Schlenk line setups and pieces of equipment is perhaps as important as knowing how to perform key Schlenk line techniques. This section will detail the advantages and disadvantages of different setups and pieces of equipment which are commonly encountered in synthetic chemistry laboratories. Product recommendations based on personal experience will also be provided in this section.
Schlenk lines are typically equipped with rotary vane (RV) vacuum pumps to achieve working pressures between 1 x 10⁻² and 1 x 10⁻⁴ mbar. RV vacuum pumps are suitable for Schlenk line chemistry due to their excellent vapour handling capability and ease of maintenance (see The 7 Golden Rules of Vacuum Pump Maintenance). The Edwards and Vacuubrand vacuum pumps are popular choices in university research labs.
High vacuum lines are equipped with oil diffusion or turbomolecular pumps to reach ultimate vacuums between 1 x 10⁻⁴ and 1 x 10⁻⁷ mbar. High vacuum lines are similar to Schlenk lines but employ vacuum transfer techniques to manipulate gases and liquids.
Flexible hosing or tubing allow Schlenk flasks and other glassware to be connected to the Schlenk line and manipulated under vacuum or an inert gas atmosphere. Many options are available and they come in a range of materials, degrees of permeability and cost. Tygon tubing is made from a thermoplastic and exhibits many desirable characteristics such as transparency, light weight and chemical resistance. Because it is transparent, it is easy to see if the tubing is contaminated and needs to be replaced. Some plastic tubing may contain dioctyl phthalate as a plasticiser which can easily leach into reactions with solvent vapours and plague NMR spectra. Silicone tubing is also available but has limited chemical resistance and is less well suited for vacuum applications. Vacuum grade rubber tubing is also frequently employed due to its high flexibility. Rubber tubing however is non-transparent and heavy when compared to plastic tubing and it can become brittle over time.
The advantages between plastic and rubber tubing is less clear cut, and personal preference, availability and cost are likely to decide which tubing is used.
Vacuum gauges, often referred to as manometers or Pirani sensors, are used to monitor the pressure in the vacuum manifold of the Schlenk line. Many basic Schlenk lines are not be built to have a vacuum gauge permanently attached, and instead the vacuum pressure is typically measured after the initial assembly (or after cleaning) by attaching the gauge to the tubing. For very sensitive chemistry, it is often imperative to have a vacuum gauge connected directly to the vacuum manifold during day-to-day manipulations to ensure that all of the seals are tight and that reaction glassware has been sufficiently evacuated prior to use. Vacuum gauges are also extremely useful for monitoring sublimations, vacuum distillations and drying solids under vacuum.
Vacuum gauges are typically connected to the vacuum manifold of the Schlenk line through a greaseless O-ring and held securely with a clamping ring. Alternatively, a KF flange allows the vacuum gauge to be connected to the Schlenk line through a greased ground glass female joint. The VACUU.VIEW extended vacuum gauge is a compact design with a digital display that measures down to 10-3 mbar, making it suitable for Schlenk line chemistry.
Please get in contact if you have any additional queries or recommendations on Schlenk line equipment.