Charged analyte-solvent clusters created in the atmospheric pressure ion source flow into the mass spectrometer through a small diameter heated tube to liberate molecular ions.  The expanding plume of gas and clusters ions that emerges from the tube is most efficiently refocused using an electrodynamic ion funnel or more generally, some form of radio frequency (RF) stacked ring ion guide. The traditional approach to improve the sensitivity of the mass spectrometer is to increase the diameter of the tube, thus increasing gas throughput, at the expense of decreased radial heat transfer and thereby desolvation of the cluster ions.  A novel ion transfer tube with a slotted internal channel cross section was designed to provide enhanced heat transfer compared to a tube with a circular cross section and equivalent gas throughput. We will report on the evaluation of ion funnels and stacked ring ion guides required to accommodate the strongly asymmetric gas expansion profile created by the slotted tube, and to be able to operate at the highest pressure to minimize the pumping requirements.  Experimentally, the ion guides were evaluated for optimal ion transmission,  degree of ion desolvation, formation of solvent adduct ions, simplicity of construction, ruggedness transmitting crashed plasma samples, ease of cleaning, mass dependency of the amplitude tuning, and the degree RF induced fragmentation of fragile peptide ions at increased pressures.   The RF frequency and amplitude were chosen to optimize the performance at higher pressures.  These studies lead us to implement a shortened, miniaturized version of a high pressure ion funnel.    Data on a triple stage quadrupole mass spectrometer demonstrates that the ion transmission of small drug molecules into the mass analyzer has increased fivefold both in terms of peak area and height resulting in a decrease of the relative standard deviation at low sample concentrations.

High throughput atmospheric pressure interfaces for mass spectrometry

248th National Meeting (2014)

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