Electron-capturing compound

A technique known as selective electron capti sensitization has been used to increase the response of the BCD weakly electron-capturing compounds [117]. In this mode a standard electron-capture detector is used with a supply of makeup gas doped with a specific sensitizing reagent such as oxygen nitrous oxide. In this way the BCD functions as an ion-aoleculSj... 

In the sample of the old physicist, the emitted particle diflFered suflBciently from the background to be detected— when not absorbed Although less sensitively detected, the same holds true to some extent for electron-capturing compounds, such as DDT, when present in an ordinary biological sample. The main diflFerence is that there are only a few elementary particles to be considered, whereas there is a vast number of electron-capturing compounds. Thus, the ECD response will not be interpretable in proper chemical terms. 

Application of a fixed or pulsed potential to the ionization chamber allows collection of the thermal electrons establishing the standing (or baseline) current. When an electron-capturing compound enters the ionization chamber, thermal electrons are removed by formation of negative ions. The increased rate of neutralization of these ions by positive ions, or their reduced drift velocity during collection of the thermal electrons, is responsible for the detector signal. In contrast to the other ionization detectors a decrease in the detector standing current proportional to solute concentration is measured rather than an increase in the number of ions or electrons produced. 

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