Zero air refers to air supplied to analytical instruments which has hydrocarbons removed. Typical levels of hydrocarbons are less than 0.1ppm. Air with very low hydrocarbons is used in gas chromatography as the oxidant gas for an FID (flame ionization detector), FPD (flame photometric detector), or NPD (nitrogen phosphorus detector). Zero air is also used as the support gas in total hydrocarbon analyzers. For the nebulizer and exhaust system in an LC/MS zero air is a pump gas. Zero air can be supplied by gas cylinders in the lab but a more efficient and cost effective supply is from a Zero Air Generator. A zero air generator uses house compressed gas or compressed gas from a compressor to generate very low hydrocarbon air, typically <0.05ppm. The air passes through a pre-filter which removes particulates, then a catalyst which removes the hydrocarbons and finally through a post filter which removes particulates down to 0.01µm. Units are available supplying zero air from 1L/hr to 30L/hr.