Jet expansion module for liquid-sampled GC-discharge ionization detection of liquefied gases

A rugged jet expansion module was designed, built, and utilized to sample liquefied gas for gas chromatography-discharge ionization detector (GC-DID) analysis. The module is inserted at an intermediate stage between a higher pressure sample cylinder and lower pressure gas injection manifold. The title jet module permits selection of liquid-phase or vapor-phase sampling by setting the valve-cylinder orientation up or down (relative to gravity). It consists of a four-way stainless steel cross, plus the following components connected to pipe thread ports: (1) mechanical pressure gauge, -15 to +30 psig; (2) threaded nut with 0.010-in. jet orifice (connect to sample cylinder valve); (3) bellows valve (connect to GC manifold); (4) bellows valve (connect to expansion cylinder). Making use of the jet module, measurement of air concentration in [15N]ammonia and sulfur hexafluoride (single-component) samples was found to be significantly lower in the liquid phase by GC-DID. This compact apparatus enables phase-selective sampling, reduces primary manifold contamination, and improves operator safety.