Influence of Pulse Conditions on Electron Capture Response

Abstract

The response of a electron capture detector (ECD) in various pulse conditions has been studied in order to reveal the influence of background current (4) on the sensitivity of electron capturing compounds.
The variations of Ib with pulse width (tw: 0.1∼10 μsec) were measured in various pulse periods (tp: 100∼2000, μusec) at 30 V (Fig.1), and then at different levels of pulse amplitude (Fig.2). The plateau values of /b-tw curves decrease linearly with increasing tp (Fig.3). On the other hand, the number of electrons (Ne-) in the ECD cell increase, with increasing tp until saturation at about 2000 /μsec (Fig.4). The magnitude of the over-all rate constant of reactions with electrons (k, ) and the production rate of thermal electrons (kpRp) are 1.1 X 10³/ sec and 1.73 X 10¹⁰ electrons/sec, respectively.
The variations of the sensitivity of electron capturing compounds with 4 are as follows: In the shbulder of each /b-t, curve, the sensitivity becomes a maximum, and the maximum value and-its t, increase with increasing tp (Fig.5). In the plateau region, as the electron concentration in the ECD cell approaches to the steady state with increasing tp, the sensitivity increases with increasing tp up to 1000∼1500, μsec (Fig.6).