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Process Gas Chromatography FAQ

Total Gas analysis is a common method of measuring the contents of a gas phase sample. Sample flows to a detector where all the impurities are counted and continuously reported together as a single concentration.

Gas Chromatography is a common method of analyzing both qualitative (what chemical) and quantitative (how much) information about a gas phase sample. A fixed volume of sample is collected and injected into a neutral carrier gas such as N2 or H2. The carrier and sample are then directed to a chromatographic column where the sample is separated into its constituent parts. The exit of the column is, in turn, attached to one or more detectors which quantify the individual target chemicals as they flow out of the column.

This GC process differs from Total Gas because the separation of the gasses in the column is a batch process which requires time to complete. Total Gas provides continuous reporting of the sum of the impurity concentrations, GC provides scheduled reports of individual species and their concentration.

This feature allows one or more species in an application to be calibrated based on another species response. This in turn, allows the user to utilize a calibration gas which does not contain all of the species in the application. For example, a BTEX in Ambient Air application could be calibrated using a standard which contains only Benzene in a balance of air with the TEX portion calibrated by RRF.

The use of RRF is based on the fact that, in a given detection system (PID for example), detector response to detectable compounds is inherently linear and consistently proportional to other compounds. For example, on most PIDs signal response to Benzene is approximately double the response for a similar concentration of iso-butylene.