Correlations and constants in unipolar and bipolar electron-capture detection

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Journal of Chromatography A





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Measurements of baseline current and response have been carried out in a small-volume electron-capture detector to prove or disprove a recent hypothesis describing its behaviour under a.c.-drive conditions. The measurements supported fully the postulated contribution of the reversed-field a.c. phase to both current and response. In particular, the predicted linear rise of both current and response was found at a.c. frequencies up to 100-200 Hz; and the end of this linear range coincided with the end of steady-state conditions during the reversed-field phase. Essentially similar steady-state limits were found under conventional, unipolar pulse regimes. This supported the hypothesis of response largely originating from the capture of electrons during the reversed-field phase, but expressing itself only through the transport of electrons during the regular-field phase of the a.c.-pulse regime. An order-of-magnitude calculation based on several hypothetical and necessary simplifications showed that the steady-state cation concentration increases with increasing amounts of SF6 in nitrogen. Correspondingly, the apparent cation-electron recombination constant (about 3 · 10-5 cm3 s-1) was almost two orders of magnitude larger than the cation-anion neutralization constant (about 4 · 10-7 cm3 s-1). © 1987.