INTERACTION OF GAS-PHASE ORGANIC-MOLECULES WITH ALUMINUM AND ELECTROPOLISHED STAINLESS-STEEL TUBING

The interaction of gas-phase species with metal surfaces is an importa nt problem, In gas analysis, it affects the delivery of atmospheric sa mples to analytical equipment through metal tubing and the storage of samples and calibration standards in cylinders and other containers, I n this paper we describe a technique for injecting a pulse of gas with a parts-per-million (by volume) level of the molecule of interest int o a stream of pure gas flowing through a sample of metal tubing, On th e basis of the deformation of the pulse due to the tubing, the interac tions between the tubing surface and the gas-phase molecule can be inv estigated. In the case of toluene interacting with electropolished sta inless steel, for example, the degree of interaction is much less when the moisture concentration in the gas is 3 ppm than when it is <0.1 p pm, For methanol interacting with aluminum, avery strong interaction i s observed which is dramatically reduced by a suitable acid-washing of the tubing, X-ray analysis of the aluminum tubing surface, coupled wi th electron microscopy, indicates that this reduction in interaction i s correlated with a decrease in surface oxide layer thickness and may be most simply explained by a reduction in surface porosity following the acid wash treatment.