An analytical model for the optimum drift voltage of drift tube ion mobility spectrometers with respect to resolving power and detection limits

One of the key experimental parameters of measurements using a drift tube ion mobility spectrometer is the drift voltage applied across its length, as it governs a multitude of processes during the ion drift. While the effect of the drift voltage on the resolving power has already been well-described, only little attention has been paid so far to developing an equally sophisticated model for the effect on the limits of detection. In this work, we extend our previous model for the resolving power and signal-to-noise-ratio of a drift tube ion mobility spectrometer operated at the resolving power optimal drift voltage to arbitrary drift voltages. It is shown that the deviation from this operating point can be completely described for any drift tube by using only the dimensionless factor beta, which is defined as the ratio between the applied drift voltage and the resolving power optimal drift voltage. From these general equations, it can be shown that the signal-tonoise-ratio and therefore the limits of detection vary much more significantly with changing drift voltage than the resolving power. Thus, it is possible to apply a higher than resolving power optimal drift voltage to lower the limits of detection with only a slight loss of resolving power. E.g., a 47.5 % higher drift voltage is able to halve the limits of detection, but yields only 8 % resolving power loss.