An Ion Funnel Interface for Improved Ion Focusing and Sensitivity Using Electrospray Ionization Mass Spectrometry

Abstract

To improve upon the already impressive sensitivity achievable with electrospray ionization sources, a novel electrohydrodynamic ion funnel interface has been developed and implemented with a triple-quadrupole mass spectrometer. The ion funnel interface effectively consists of a series of ring electrodes of increasingly small internal diameters to which rf and dc electric potentials are coapplied. In the 1-10-Torr pressure range, the electric fields cause the collisionally damped ions to be more effectively focused and transmitted as a collimated ion beam. This paper describes the ion funnel design and presents an evaluation of its performance using a triple-quadrupole mass spectrometer. Ion transmission and m/z discriminating parameters (resulting in both effective low- and high-m/z cutoffs) are presented based upon both ion current measurements and mass spectra. Electrospray ionization mass spectra of selected protein solutions demonstrated well over 1 order of magnitude increase in signal relative to that of the instrument operated in its standard (inlet capillary-skimmer) configuration under similar conditions. The present results suggest that it will be feasible to realize close to 100% ion transmission efficiency for analytically relevant ions through the electrospray ionization interface and into the mass analyzer.

Spectroscopy and dynamics of the 7,7,8,8-tetracyanoquinodimethane radical anion

“…14 The broader kinetic energy feature around 2.0 eV is somewhat unexpected. The photon energy of 3.1 eV is resonant with the D 2 state and as such, this photoelectron peak could be explained in terms of resonance-enhanced two- 25 photon absorption via the D 2 state, which has a large excitation cross-section. However, the D 2 state has a  2 2* 1 configuration which, in Koopmans' picture, correlates to the neutral in its S 0 state following detachment of an electron from the 2* (4b 3u ) orbital, thus generating photoelectrons 30 around 3.5 eV; this is not observed in the PES.…”

“…(solid black line) and reproduces the experimental data very well, particularly the deviation from exponential decay observed over the first few picoseconds. The corresponding beat in the ground state is not observed, presumably because of the significantly lower signal levels measured for this 25 feature as evidenced in Fig. 3.…”

“…Additionally, the feature at 2.0 eV is depleted. The latter is a direct measure of the D 0 state population as the only 25 process that can produce photoelectrons at this energy is resonance-enhanced two-photon detachment via the D 2 state. Depletion in this feature indicates that some population has been transferred from the ground state to the excited state.…”

“…In the condensed phase, TCNQ based CT salts owe their high conductivities to a - stacking motif, resulting in the spatial and energetic overlap between their respective -orbitals. This is exemplified by the complex of 25 the tetrathiofulvane (TTF) radical cation and the TCNQ radical anion, which is commonly regarded as the benchmark CT complex. 5 At a temperature of 66 K it possesses a conductivity of 1.47×10 4  -1 cm -1 , approaching that of copper at room temperature (6×10 5  -1 cm -1 ) and for this reason the 30 term "organic metal" has become widely used to describe these highly conductive organic salts.…”

Tissue Proteomics for the Next Decade? Towards a Molecular Dimension in Histology

“…Regarding instrumentation, the most cutting edge improvements are the gain of mass accuracy for an optimal detection of the eluted peptides during LC-MS runs (Mann and Kelleher, 2008;Michalski et al, 2011) and the increase in scanning speed, for example with the use of Orbitrap analyzers (Hardman and Makarov, 2003;Makarov et al, 2006;Makarov et al, 2009;Olsen et al, 2009). Ion transfer efficiency was also drastically improved with the conception of ion funnels that homogenize the ion transmission capacities through m/z ranges (Kelly et al, 2010;Kim et al, 2000;Page et al, 2006;Shaffer et al, 1998) or by performing electrospray ionization within low vacuum (Marginean et al, 2010;Page et al, 2008;Tang et al, 2011). Beside collision induced dissociation (CID) that is proposed for many applications Wells and McLuckey, 2005), new fragmentation methods were investigated, such as higher-energy collisional dissociation (HCD) especially for phosphoproteomic applications (Nagaraj et al, 2010), and electron transfer dissociation (ETD) and electron capture dissociation (ECD) that are suited for phospho-and glycoproteomics Boersema et al, 2009;Wiesner et al, 2008).…”