A new electrodynamic (rf) ion funnel has been developed and evaluated for use in the interface regions (at approximately 1-10 Torr) of atmospheric pressure ion sources (e.g., electrospray ionization (ESI) for mass spectrometry). The ion funnel consists of a ring electrode ion guide with decreasing i.d. and with a superimposed dc potential gradient along the ring stack. The thicknesses of the ring electrodes and the spacings between them were reduced to 0.5 mm from 1.59 mm compared to those used for previous designs. The new ion funnel displays a significant improvement in low-mass transmission (m/z >200) and sensitivity compared to previous designs. The transmission efficiencies for electrosprayed peptides and proteins (ranging in mass from 200 to 17,000 Da) were typically 50-60% of total incoming currents from a heated capillary inlet. The transmitted ion currents were a factor of 30-56 greater than those of the standard interface for peptide samples and a factor of 18-22 greater than those for protein samples. The sensitivity gains realized at the MS detector were somewhat lower, possibly due to space charge effects in the octapole ion beam guide following the ion funnel. The improved ion transmission properties result primarily from the use of reduced spacings between ring electrodes. We also show that the ion funnel can be operated in two different modes, one using low-rf-amplitude scans, allowing fragile noncovalent complexes (as well as generally undesired adducts) to be transmitted, and the other using high-rf-amplitude scans, providing greater collisional activation and more effective adduct removal (or the dissociation of lower m/z species).

Arrays of microelectrospray emitters were fabricated on polycarbonate substrates using a laser etching technique. Stable multielectrosprays were successfully generated in the liquid flow rate range relevant to mass spectrometric applications. Comparison of electrosprays generated from the microfabricated emitter array and conventional fused-silica capillaries showed similar spray characteristics and reliability. Higher total electrospray ion currents were observed as the number of electrosprays increased at a given total liquid flow rate. Consistent with the theoretical prediction, the total spray current at a constant total liquid flow rate was shown experimentally to be approximately proportional to the square root of the number of electrosprays. It is further projected that when total flow rate is optimized the maximum achievable total current will be proportional to the number of emitters. Evaluation of the multielectrospray device using a triple quadrupole mass spectrometer showed a factor of 2-3 sensitivity enhancement for the spray numbers ranging from two to nine compared to a conventional single electrospray ionization source under the same operating conditions.

A new multicapillary inlet and ion funnel interface for electrospray ionization-mass spectrometry has been developed and demonstrated to achieve higher ion transmission efficiency compared to a single-capillary inlet and ion funnel interface. Even though the distance between the end of the ESI inlet capillary and the exit of the ion funnel (10 cm) is significantly longer than that of the conventional interface (typically a few millimeters), a significant part of the directed inlet gas flow persists into the first stage of pumping and results in an increased gas load to the second chamber. A jet disrupter made of a circular metal disk placed on axis in the ion funnel enhanced the dispersion of the directed gas flow from a multicapillary inlet and was also found to improve the ion transmission. The ion funnel with the jet disrupter demonstrated a 15% improvement in ion transmission (compared to that without the jet disrupter) and simultaneously reduced the pumping speed required for the first or second stage by a factor of 2-3. Compared to the sensitivity with the standard mass spectrometer interface (an API 3000, Sciex, Concord, ON, Canada) in MS/MS operation using an interface equipped with the jet disrupter and ion funnel, a 5.3-10.7-fold enhancement in signal was observed for samples with concentrations of 100-500 pg/microL and 10.2 to 14.1-fold enhancement for concentrations of 10 to 50 pg/microL. The decreased enhancement at higher concentrations is attributed to space charge effects and detector saturation.