The gases desorb from the column and enter the detector separately, allowing identification and quantification. Each substance generates a concentration pulse as it enters the detector. This pulse is recorded as a chromatogram, a graph showing the detector response as a function of elution time. The number of peaks on a chromatogram reflects the number of components present in the sample. The position of the peaks, which reveal retention times when they are compared with known standards, allow identification of the sample gas components.
Retention time is the time it takes for the peak to reach the detector after injection.
The height and areas of the peaks show the quantity of each component. Unlike many other gas analysis methods, GC operates at atmospheric pressure, creating special requirements for the sampling system. Some sterilization cycles condition at very low pressures. The dynamic environmental conditioning cycle, for example, conditions at less than 1.0 psia. Therefore, sampling for EtO during the sterilant dwell cycle, which usually occurs close to or above atmospheric pressure, is easier because the pressure difference between the GC and the sterilizer offers less resistance than in other cycles.