The influence of diffusion on the current-voltage curve in a flame ionization detector

Abstract

An earlier analysis of the electric current carried by positive ions from the flame in a flame ionization detector is extended to include the effect of the diffusion of the ions. It had been noted that the earlier theory gave a current-voltage expression from which the experimental measurements diverged at very low values of the voltages. Solutions of the nonlinear differential equations for the electric field are presented here in both one and two dimensions, the latter being the experimental cylindrical arrangement of the flame ionization detector. A partial explanation is given for the behaviour at low currents.