The Air Liquide Encyclopaedia of Gases (Published by Elsevier Press) lists 138 pure gases. In addition to this for calibration requirements there are a myriad of different mixtures available, all developed for specific applications. Depending on the application some of these mixtures have limited shelf life and so may be mixed to order.

For many analytical applications there are only 9 pure gases that are in common usage. These are Nitrogen; Hydrogen; Helium; Argon; Oxygen; Acetylene; Carbon Dioxide; Nitrous Oxide and Air ( either compressed or Synthetic).

The one potentially confusing point here is that Air is not generally classed as a mixture but a pure gas. In all cases it is important to understand the properties of a gas, particularly in terms of flammability, toxicity, asphyxiation dangers and oxidising potential. In all cases it is essential to obtain a copy of the Material Safety Datasheet as part of the risk assessment on the use of a gas.