Influence of Carrier Gas Flow-Rate on the Response of an Electron Capture Detector

Abstract

Influence of carrier gas flow-rate on the response of the electron capture detector (ECD) operated in the pulse-sampling mode was studied. The variations of the background current with carrier gas flow-rate (20-440 miimin) were measured in various pulse periods (10-2000 ju see). In the case of short pulse periods (below 100 p sec), almost no influence of carrier gas flow-rate on the background current is recognized, regardless of the column temperature. p In the case of long pulse periods (over 500sec), the background current drops with decreas- ing flow-rate, and the degree of the drop becomes more remarkable increasing pulse period and/or rise in the column temperature. It is considered that these phenomena are caused by the electron capturing species diffusing from the column even when pure carrier gas flows. The electron capture coefficient in a pulse period of 1000 p sec, K1000, is about 5-6 times as large as that of 100 p sec, K100. Both K100 and K1000 are constant at the carrier gas flow-rate above 60 and 80 m//min, but decrease with decreasing carrier gas flow-rate below 60 and 80 m//min, respectively. These results suggest that as the carrier gas flow-rate is less than the values described above, the concentration of the sample gas in the ECD, to which the response is proportional, becomes less homogeneous.