Gas is often the last point on procurement, or the end-user’s, mind when it comes to purchasing a critical piece of analytical equipment, such as a mass spectrometer (MS).
Even further down the list of concerns is the type of tubing used to connect the gas supply to the workhorse of the laboratory. It can however be one of the most important factors affecting data quality, especially as MS sensitivity and resolution is greatly improving with each new generation.
Gas supplied from a generator will usually be connected to a mass spectrometer by flexible tubing and secured by SwagelokTM, or similar, connection. There are several typical types and diameter of tube that can be used and should be sized based on the distance from point of use and application.
PTFE (Polytetrafluoroethylene) aka Teflon tubing is used in many sensitive applications due to its inert property with many inorganic and organic chemicals, oils and fluids. PTFE tubing have excellent weatherability including low and high temperature capability, low friction and resistance to UV damage. Furthermore, it is the most flexible of all the fluoropolymer tubing and is FDA compliant. These properties are why PTFE would always be the preferred material for gas delivery lines to MS applications.
PE (Polyethylene) comes in many grades and has excellent chemical resistance, absorbing almost no water, and has a lower gas and water vapor permeability (for polar gases) than most other plastics. PE can be suitable for gas delivery but, for high sensitivity applications, PTFE is the best option. PE tubing is generally provided for drain lines.
Aside from tubing, one may want to check not only the tubing type, but for damaged or bad fittings that could lead to impurities entering the gas stream, decreasing gas purity and compromising MS background and data integrity overall.