Gas Chromatography - Gas Supplies > Supplies from Gas Tanks and Pure Air Generators > Page 5
Gases for use with the gas chromatograph were originally all obtained from gas tanks or gas cylinders. However, over the past decade the use of gas generators have become more popular as it avoids having gases at high pressure in the laboratory which is perceived by some as potentially dangerous. In addition, the use of a hydrogen generator avoids the use of a cylinder of hydrogen at high pressure which is also perceived by some as a serious fire hazard despite the fact that they have been used in laboratories, quite safely for nearly a century.
Supplies from Gas Tanks
Gasses are stored in large cylindrical tanks fitted with reducing valves that are set to supply the gas to the instrument at the recommended pressure defined by the manufacturers. The cylinders are often situated outside and away from the chromatograph for safety purposes and the gasses are passed to the chromatograph through copper or stainless steel conduits at relatively low pressure. The main disadvantage of gas tanks is their size and weight which makes them difficult to move and replace.
Pure Air Generators.
Air generators require an air supply from air tanks or directly from the laboratory compressed air supply. The Packard Zero Air Generator passes the gas through a 0.5 m filter to remove oil and water and finally over a catalyst to remove hydrocarbons. The hydrocarbon free air is then passed through a 0.01 m cellulose fiber filter to remove any residual particulate matter that may be present. The manufacturers claim the resulting air supply contains less than 0.1 ppm total hydrocarbons and delivers air at 125 psi at flow rates up to 2,500 cc per min.