ABSTRACT
Standard calibration mixtures of one or several of the common hydrocarbons in air are available commercially in high-pressure gas cylinders. The most abundant hydrocarbon, methane, is nonreactive in photochemical reactions and is a less hazardous air pollutant. The hydrocarbon will effuse through the walls of a given tube at a rate depending only on temperature, as long as some liquid remains. Flame ionization detectors are used to measure total hydrocarbons for pollution, leakage, or safety monitoring. In dual-flame detectors the concentration of total hydrocarbons and methane can be separately identified. The only practical method for general analysis of specific hydrocarbons is gas chromatography. Calibration is based on the fact that under carefully reproduced conditions, a given hydrocarbon will always require the same length of time to pass through the column to the detector. The hydrocarbon dew point of natural gas is that temperature at which the first significant amounts of condensate are formed on a chilled surface.
