Measurements of ions within an electron capture detector (ECD) have been made by the technique of atmospheric pressure ionization mass spectrometry (APIMS) where the ion source has been modified to be an actual ECD. By observing the dependence of ion signals on electrostatic fields applied to the ionization cell, new insight into the role of ions in influencing the measured ECD current is provided. I t is shown that for this pulsed ECD, a positive current of significant magnitude exists which is an integral component of the normally measured ECD current, and that it is caused by the selective migration of positive ions to the sampling electrodeduring the period between pulses. The results are discussed relative to opposing views of the ECD, and are shown to strongly support one of these.

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