Electron-capture detector response characteristics

The device functions in the same way as the conventional electron-capture detector with a radioactive source. The column eluent enters just below the third electrode, any electron-capturing substance present removes some of the free electrons, and the current collected by the fourth electrode falls. The sensitivity claimed for the detector is 0.2-1.0 ng, but this is not very informative as its significance depends on the characteristics of the column used and on the k of the solute peak on which the measurements were made. The sensitivity should be given as that solute concentration that produces a signal equivalent to twice the noise. Such data allow a rational comparison between detectors. The sensitivity or minimum detectable concentration of this detector is probably similar to the conventional pulsed ECD (viz. 1 X 10 g/mL). The linear dynamic range appears to be at least three orders of magnitude for a response index of r, where 0.97 [Pg.607]

Some FDD detectors also offer an electron capture mode being selective for monitoring high electron affinity compounds such as freons, chlorinated pesticides and other halogen compounds. For such type of compounds, the minimum detectable quantity (MDQ) is at the femtogram or low picogram level. The FDD is similar in sensitivity and response characteristics to a conventional radioactive ECD, and can be operated at temperatures up to 400 °C. For operation in this mode. He and CH are introduced just upstream from the column exit. 

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