Dipolar DC induced collisional activation of non-dissociated electron-transfer products.

The application of electron transfer and dipolar direct current induced collisional activation (ET-DDC) for enhanced sequence coverage of peptide/protein cations is described. A DDC potential is applied across one pair of opposing rods in the high-pressure collision cell of a hybrid quadrupole/time-of-flight tandem mass spectrometer (QqTOF) to induce collisional activation, in conjunction with electron transfer reactions. As a broadband technique, DDC can be employed for the simultaneous collisional activation of all the first-generation charge-reduced precursor ions (eg, electron transfer no-dissociation or ETnoD products) from electron transfer reactions over a relatively broad mass-to-charge range.

Maximizing Ion Transmission in Differential Mobility Spectrometry.

We provide modeling and experimental data describing the dominant ion-loss mechanisms for differential mobility spectrometry (DMS). Ion motion is considered from the inlet region of the mobility analyzer to the DMS exit, and losses resulting from diffusion to electrode surfaces, insufficient effective gap, ion fragmentation, and fringing field effects are considered for a commercial DMS system with 1-mm gap height. It is shown that losses due to diffusion and radial oscillations can be minimized with careful consideration of residence time, electrode spacing, gas flow rate, and waveform frequency.

Gas-Phase Chemical Separation of Phosphatidylcholine and Phosphatidylethanolamine Cations via Charge Inversion Ion/Ion Chemistry.

The [M + H](+) cations formed upon electrospray ionization of the glycerophospholipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE) show distinct reactivities upon gas-phase reactions with doubly deprotonated 1,4-phenylenedipropionic acid (PDPA). PC cations undergo charge inversion via adduct formation with subsequent methyl cation and proton transfer to the acid to yield [PC - CH3](-) anions. These demethylated PC anions fragment upon ion trap collision-induced dissociation (CID) to yield products that reveal fatty acid chain lengths and degrees of unsaturation.

Differential mobility spectrometry/mass spectrometry history, theory, design optimization, simulations, and applications.

This review of differential mobility spectrometry focuses primarily on mass spectrometry coupling, starting with the history of the development of this technique in the Soviet Union. Fundamental principles of the separation process are covered, in addition to efforts related to design optimization and advancements in computer simulations. The flexibility of differential mobility spectrometry design features is explored in detail, particularly with regards to separation capability, speed, and ion transmission.

Assignment of the stereochemistry and anomeric configuration of sugars within oligosaccharides via overlapping disaccharide ladders using MS(n).

A systematic approach is described that can pinpoint the stereo-structures (sugar identity, anomeric configuration, and location) of individual sugar units within linear oligosaccharides. Using a highly modified mass spectrometer, dissociation of linear oligosaccharides in the gas phase was optimized along multiple-stage tandem dissociation pathways (MS(n), n = 4 or 5). The instrument was a hybrid triple quadrupole/linear ion trap mass spectrometer capable of high-efficiency bidirectional ion transfer between quadrupole arrays.

Trapping mode dipolar DC collisional activation in the RF-only ion guide of a linear ion trap/time-of-flight instrument for gaseous bio-ion declustering.

The application of dipolar direct current (DDC) to the radio frequency-only ion guide (Q0) of a hybrid quadrupole/time-of-flight mass spectrometer for collision-induced declustering of large bio-ions is described. As a broadband technique, ion trap DDC collisional activation (CA) is employed to decluster ions simultaneously over a relatively broad mass-to-charge (m/z) range. Declustering DDC CA can yield significantly narrower peaks relative to those observed in the absence of declustering methods, depending upon the extent of noncovalent adduction associated with the ions, and can also be used in conjunction with other methods, such as nozzle-skimmer CA.

Implementation of dipolar direct current (DDC) collision-induced dissociation in storage and transmission modes on a quadrupole/time-of-flight tandem mass spectrometer.

Means for effecting dipolar direct current collision-induced dissociation (DDC CID) on a quadrupole/time-of-flight in a mass spectrometer have been implemented for the broadband dissociation of a wide range of analyte ions. The DDC fragmentation method in electrodynamic storage and transmission devices provides a means for inducing fragmentation of ions over a large mass-to-charge range simultaneously. It can be effected within an ion storage step in a quadrupole collision cell that is operated as a linear ion trap or as ions are continuously transmitted through the collision cell.

Tandem ion trap design with enhanced mass analysis capabilities for large populations of ions.

A new arrangement consisting of two separate radio frequency (rf) quadrupole ion traps is used to analyze large populations of ions over a wide mass-to-charge (m/z) range. The setup consists of an "accumulation" trap that is maintained at a higher pressure than the second high-performance "analyzer" trap. The two traps are scanned simultaneously, with a mass difference between that determines the residence time and mass range of ions in the analytical trap.

Tailored-waveform collisional activation of peptide ion electron transfer survivor ions in cation transmission mode ion/ion reaction experiments.

Broadband resonance excitation via a tailored waveform in a high pressure collision cell (Q2) on a hybrid quadrupole/time-of-flight (QqTOF) tandem mass spectrometer has been implemented for cation transmission mode electron transfer ion/ion reactions of tryptic polypeptides. The frequency components in the broadband waveform were defined to excite the first generation intact electron transfer products for relatively large tryptic peptides. The optimum amplitude of the arbitrary waveform applied has been determined empirically to be 3.

Transmission mode ion/ion reactions in the radiofrequency-only ion guide of hybrid tandem mass spectrometers.

Transmission mode ion/ion reactions have been performed within the first quadrupole, the Q0 radiofrequency (RF)-only quadrupole, of two types of hybrid tandem mass spectrometers (viz., triple quadrupole/linear ion trap and QqTOF instruments). These transmission mode reactions involved the storage of either the reagent species and the transmission of the analyte species through the Q0 quadrupole for charge inversion reactions or the storage of the analyte ions and transmission of the reagent ions as in charge reduction experiments.

Study of the enhancement of dipolar resonant excitation by linear ion trap simulations.

Resolution improvements in dipolar resonant excitation have been examined in a round-rod quadrupolar collision cell for values of the Mathieu characteristic exponent beta equal to n/p, where n and m are small integers (prime beta values) versus other beta values where n and p are not small (ordinary beta values). The trajectories of ions moving in the time-varying electric fields of a quadrupole with and without buffer-gas molecules were calculated to determine the relationship of prime and ordinary beta values to frequency resolution for resonant ion excitation and ejection. For prime beta values, the ion trajectory in the hyperbolic quadrupole field will be exactly periodic with a period of at most 4 pi p/Omega, where Omega is the angular frequency of the main drive radio-frequency (RF) potential.

Implementation of ion/ion reactions in a quadrupole/time-of-flight tandem mass spectrometer.

A commercial quadrupole/time-of-flight (QqTOF) tandem mass spectrometer has been adapted for ion/ion reaction studies. To enable mutual storage of oppositely charged ions in a linear ion trap, the oscillating quadrupole field of the second quadrupole of the system (Q2) serves to store ions in the radial dimension while auxiliary radio frequency is superposed on the end lenses of Q2 during the reaction period to create barriers in the axial dimension. A pulsed dual electrospray (ESI) source is directly coupled to the instrument interface for the purpose of proton transfer reactions.

Linear quadrupoles with added hexapole fields.

Linear quadrupoles with added hexapole fields are described. The shifts in ion oscillation frequency caused by the addition of a hexapole field are calculated within the effective potential model. Methods to construct linear quadrupoles with added hexapole fields with exact electrode geometries and with round rods are discussed.

Mutual storage mode ion/ion reactions in a hybrid linear ion trap.

Ion/ion proton transfer reactions involving mutual storage of both ion polarities in a linear ion trap (LIT) that comprises part of a hybrid triple quadrupole/linear ion trap mass spectrometer have been effected. Mutual ion storage in the x- and y-dimensions arises from the normal operation of the oscillating quadrupole field of the quadrupole array, while storage in the z-dimension is enabled by applying unbalanced radio-frequency amplitudes to opposing sets of rods of the array. Efficient trapping (>90%) is achieved for thermalized ions over periods of several seconds.

Positive ion transmission mode ion/ion reactions in a hybrid linear ion trap.

A triple quadrupole mass spectrometer capable of ion trapping experiments has been adapted for ion/ion reaction studies. The instrument is based on a commercially available linear ion trap (LIT) tandem mass spectrometer (i.e.