Mass spectrometry continues to develop as a valuable tool in the analysis of proteins and protein complexes. In protein complex mass spectrometry studies, surface-induced dissociation (SID) has been successfully applied in quadrupole time-of-flight (Q-TOF) instruments. SID provides structural information on noncovalent protein complexes that is complementary to other techniques. However, the mass resolution of Q-TOF instruments can limit the information that can be obtained for protein complexes by SID. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides ultrahigh resolution and ultrahigh mass accuracy measurements. In this study, an SID device was designed and successfully installed in a hybrid FT-ICR instrument in place of the standard gas collision cell. The SID-FT-ICR platform has been tested with several protein complex systems (homooligomers, a heterooligomer, and a protein-ligand complex, ranging from 53 to 85 kDa), and the results are consistent with data previously acquired on Q-TOF platforms, matching predictions from known protein interface information. SID fragments with the same m/z but different charge states are well-resolved based on distinct spacing between adjacent isotope peaks, and the addition of metal cations and ligands can also be isotopically resolved with the ultrahigh mass resolution available in FT-ICR.

The sizes and shapes of nanoparticles play a critical role in their chemical and material properties. Common sizing methods based on light scattering or mobility lack individual particle specificity, and microscopy-based methods often require cumbersome sample preparation and image analysis. A promising alternative method for the rapid and accurate characterization of nanoparticle size is charge detection mass spectrometry (CDMS), an emerging technique that measures the masses of individual ions. A recently constructed CDMS instrument designed specifically for high acquisition speed, efficiency, and accuracy is described. This instrument does not rely on an ion energy filter or estimates of ion energy that have been previously required for mass determination, but instead uses direct, in situ measurements. A standardized sample of ∼100 nm diameter polystyrene nanoparticles and ∼50 nm polystyrene nanoparticles with aminefunctionalized surfaces are characterized using CDMS and transmission electron microscopy (TEM). Individual nanoparticle masses measured by CDMS are transformed to diameters, and these size distributions are in close agreement with distributions measured by TEM. CDMS analysis also reveals dimerization of ∼100 nm nanoparticles in solution that cannot be determined by TEM due to the tendency of nanoparticles to agglomerate when dried onto a surface. Comparing the acquisition and analysis times of CDMS and TEM shows particle sizing rates up to ∼80× faster are possible using CDMS, even when samples ∼50× more dilute were used. The combination of both high-accuracy individual nanoparticle measurements and fast acquisition rates by CDMS represents an important advance in nanoparticle analysis capabilities.

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Abstract. The Loeb-Eiber mass filter is best operated at relatively high pressures-such as 1 Torr-where collisional dampening of ions up to the mass filter thermalizes the ions' kinetic energy, which is a requirement for effective filtering. The inter-electrode gaps of~8 μm require rf amplitudes on the order of 0-5 V p-p at approximately 50 MHz to achieve mass filtering up to m/z 40. Mass filtering between the 25-μm diameter wires, therefore, takes place on time frames less than the collision frequency at~1 Torr. The low power and high pressure capabilities of the Loeb-Eiber mass filter make it ideally suited for miniaturization, where power and space are a premium. In the present work, a Loeb-Eiber mass filter was constructed using commercial silicon-on-insulator (SOI) microfabrication techniques. Ions transmitting through the chip-based Loeb-Eiber mass filter were characterized in real time using a traditional linear quadrupole mass analyzer in series with the Loeb-Eiber mass filter. The new hybrid instrument has enabled us to verify several important claims regarding the operation of the Loeb-Eiber mass filter: (1) that ions can be effectively filtered at~1 Torr, (2) that for ions of a fixed mass-to-charge ratio, the ion transmission current decreases linearly with increasing rf amplitude on the Loeb-Eiber mass filter, (3) that the cutoff voltage at which all ions of a particular m/z value are effectively blocked is linearly related to mass-to-charge, and (4) that square waveforms can filter ions more effectively than sinusoidal waveforms for a given peak-to-peak rf amplitude.