Fittings and gas purity

Basically, the point to remember is "the fewer the better". Every connection in your gas delivery system has the potential for leaks; the more fittings you have, the greater the potential. In the illustration below, several gas purification options are depicted:

A. The Mat/Sen gas specific purifier minimizes the number of fittings. Total fittings: 2

B. The "Manifold System" has two compression fittings for the system and one organic O-ring seal for each cartridge. Total fittings: at least 5

C. A typical "Contaminant Trap" configuration has several components. Before the gas supply even enters the GC there are at least 4 modules. Total fittings: at least 8

Further reference

Gas purifiers
Carbon dioxide gas purifier
Contaminant traps
Valco helium purifier (a heated purifier for maximum nitrogen removal)