An ion trap interface for ESI-ion mobility experiments

A method for improving the sensitivity of ion mobility measurements of ions generated from continuous ionization sources such as electrospray ionization is described. The method involves an ion trap interface between the continuous source and the pulsed experiment. The trap allows the electrosprayed ion beam to be accumulated between pulses of the mobility experiment and provides tightly focused (both spatially and temporally) ion pulses for initiating experiments. Using this method, we have improved signal-to-noise ratios by factors of similar to 10-30 compared with those of existing approaches and achieved experimental duty cycles of nearly 100%. With these improvements, it is possible to record complex ion mobility distributions in less than 10 s, and we have obtained detection limits of 1.3 pmol for the oligosaccharide maltotetraose. A detailed description of the experimental arrangement is given. An application of the improved methods in which collision-induced fragmentation of biomolecules is monitored by ion mobility spectrometry is described.