On the resolution, sensitivity and ion transmission efficiency of a planar FAIMS

A detailed experimental characterization and theoretical analysis on the sensitivity, resolution and ion transmission efficiency of a planar FAIMS under different operating conditions including electrospray flow rate, solution concentration, curtain voltage and dispersion voltage are reported in the study based on the direct measurements of the ion current on the FAIMS detector. The sensitivity of FAIMS was shown to increase initially with the increase of electrospray flow rate. At a certain flow rate, which is typically compound dependent, an optimum FAIMS sensitivity was observed. Further increasing the electrospray flow rate would result in the decrease of the FAIMS sensitivity. Interestingly, the ion transmission efficiency of the FAIMS was shown experimentally to monotonically increase with the decrease of the electrospray flow rates. Both the ion transmission efficiency/sensitivity and the resolution of the FAIMS were significantly affected by the dispersion voltage. There is a strong tradeoff between the FAIMS ion transmission efficiency/sensitivity and separation resolution. As the FAIMS dispersion voltage increases, the separation resolution increases while the ion transmission efficiency/sensitivity decreases. The curtain voltage can also dramatically affect the performance of FAIMS, especially in the ion separation mode. The sensitivity of FAIMS at curtain voltage of 1.8 kV is about two-fold higher than the one at 1.0 kV. This study allows one to select the desirable FAIMS operating conditions based on the actual analysis needs.