A novel quadrupole,quistor, quadrupole tandem mass spectrometer

A quadrupole, quistor, quadrupole tandem mass spectrometer allowing selected ion/selected molecule reactions was built. The quistor will be used as a reaction chamber for the study of organic ion-molecule reactions. Ions are generated in a differentially pumped ion source, quadrupole mass selected and injected into the quistor. The ions are trapped in the quistor by the combined action of a deceleration lens, the presence of helium buffer gas and the quistor RF field. As a first test of the performance of the instrument, the reaction rate constant of the reaction of O₂⁺˙ with methane was measured to be 5 × 10^?12 cm³s^?1. This is in good agreement with literature values, indicating that the ions are near thermal equilibrium after a few milliseconds of trapping time.     

A novel tandem quadrupole mass analyzer

A new “tandem mass analyzer” is described. Two quadrupole mass filters are operated in series. Each is operated at low resolution and a small mass offset is introduced between the two quadrupoles so that the pair operate together to give higher resolution. The resolution of the tandem analyzer can be changed by changing the mass offset. The transmission is highest when the quadrupoles are operated as close together as possible with the poles aligned, with no intervening ion lens, and with the radio frequency (rf) voltages phase locked. A phase shift between the rf voltages applied to the quadrupoles also improves the ion transmission. For a given resolution the tandem analyzer has transmission comparable to that of a single quadrupole. Results obtained with operation of the quadrupoles in the first, second, and third stability regions are described. Operation in the third stability region is particularly advantageous because the tandem analyzer exhibits good abundance sensitivity on the low and high mass sides under conditions where a single quadrupole produces a long peak tail on at least one side. It is also shown that scattering losses in the tandem analyzer are about half of those of a conventional quadrupole. The results suggest that it may be possible to build a low cost tandem analyzer that has relatively poor mechanical precision and yet that produces satisfactory peak shape and resolution.     

Electron impact mass spectra of some anthracene,anthrafuran and nitroanthrafuran derivatives. A tandem mass spectrometric collisional activation dissociation study

The 70-eV electron impact mass spectra of a series of thirty anthracene, seven anthra[2,1-b]furan and seven 2-nitroanthra[2,1-b]furan derivatives are described and discussed. A collisional activation dissociation study of 1-formyl-2,6-dimethoxy-9-methyianthracene, 1-formyl-2,6-dimethoxy-10-methylanthracene, and 2-carboxy-11-methylanthra[2,1-b]furan has been carried out using tandem mass spectrometry in order to substantiate the fragmentation schemes.     

Photon-induced dissociation with a four-sector tandem mass spectrometer

The feasibility of using photodissociation of protonated peptide molecules to sequence specific fragment ions with a 193-nm pulsed laser beam in a magnetic deflection tandem mass spectrometer of EBEB configuration was demonstrated. Although the short pulse (15 ns) and low repetition rate (100 Hz) of the excimer laser permitted the irradiation of only ～ 0.02% of the (M + H)⁺ ions exiting MS-1, a photon-induced decomposition spectrum of the heptapeptide angiotensio III (M _r 930.5) was produced that was practically the same (but with better signal-to-noise ratio) as that generated by collision-activated dissociation at the same low duty cycle. Because of the low and pulsed fragment ion currents, an array detector was used to record the spectra. A dependence between laser power and abundance of fragment ions was observed (increased power increases the relative abundance of ions of low mass). Laser power was varied from 6 to 80 mJ. Formation of fragment ions from a large peptide (melittin, M, 2844.75) was also observed. The results permit the design of modifications that may increase the fragment ion yield to 10% or higher, which would make photon-induced decomposition a useful method for magnetic deflection mass spectrometers.     

Energy-resolved collisional activation of dimethyl phosphonate and dimethyl phosphite ions in a quadrupole ion trap and a triple quadrupole mass spectrometer

Collision-activated dissociation spectra of dimethyl phosphonate and dimethyl phosphite ions were measured as a function of the amplitude of a supplementary AC voltage applied across the end-caps of an ion-trap mass spectrometer. These spectra yield breakdown graphs which bear a close resemblance to those obtained by varying collision energy in a triple-quadrupole mass spectrometer operating under multiple-collision conditions. Variation in the time of excitation at the resonance frequency provides an alternative route to breakdown graphs. The results demonstrate that energy deposition occurs via multiple activating collisions in the ion trap. Maximum energy deposition observed is somewhat smaller under normal operating conditions in the ion trap than in the triple-quadrupole mass spectrometer.     

A study of resonance electron capture ionization on a quadrupole tandem mass spectrometer

Procedures that allow the realization of resonance electron capture (REC) mode on a commercial triple-quadrupole mass spectrometer, after some simple modifications, are described. REC mass spectrometry (MS) and tandem mass spectrometry (MS/MS) experiments were performed and spectra for some compounds were recorded. In particular, the charge-remote fragmentation (CRF) spectra of [M - H](-) ions of docosanoic and docosenoic acids under low-energy collisionally activated dissociation (CAD) conditions were obtained, and showed that there were no significant differences for [M - H](-) ions produced at different resonances (i.e. for [M - H](-) ions with different structures). This observation was explained on the basis of results obtained from deuterium-labeled fatty acids, which showed that different CRF ions (but with the same m/z value in the absence of labels) could be produced by different mechanisms, and all of them were obviously realized under CAD conditions that made spectra practically indistinguishable. The other example, which compared the REC-MS/MS spectrum of [M - H](-) ions and EI-MS/MS spectrum of M(+.) ions of daidzein, demonstrated the potential of the REC-MS/MS technique for more complex structure elucidation.     

Surface-induced dissociation in tandem quadrupole mass spectrometers: A comparison of three designs

Three different devices that-can be used for surface-induced dissociation (SID) m tandem quadrupole instruments are compared here. The designs were compared by examining the fragmentation of several compounds including benzene, W(CO)₆, and (CH₃)₄N⁺. These studies show that SID can be readily implemented on a variety of tandem quadrupoIe instruments and that the spectra obtained with the in-line and 90° instruments are similar. Evidence is presented that confirms that high average internal energies and narrow distributions of internal energy are available by this technique. Efficiencies for fragmentation of odd-electron ions are on the order of those previously reported by others. The overall SID efficiency for even-electron ions is higher than that for odd-electron ions of similar structure.     

Surface-induced dissociation of molecular ions in a quadrupole ion trap mass spectrometer

A method is reported by which surface-induced dissociation is used to activate ions stored in a quadrupole ion trap mass spectrometer. The method employs a short (< 5 μs), fast-rising (< 20-ns rise time), high voltage direct current (dc) pulse, which is applied to the endcaps of a standard Paul-type quadrupole ion trap. This is in contrast to the application of an alternating current (ac) signal normally used to resonantly excite and dissociate ions in the trap. The effect of the dc pulse is to cause the ions rapidly to become unstable in the radial direction and subsequently to collide with the ring electrode. Sufficient internal energy is acquired in this collision to cause high energy fragmentations of relatively intractable molecular ions such as pyrene and benzene. The dissociations of limonene are used to demonstrate that high energy demand processes increase in relative importance in the dc pulse experiment compared with the usual resonance excitation method used to cause activation. The fragments are scanned out of the ion trap using the conventional mass-selective instability scan mode. Simulations of ion motion in the trap provide evidence that surface collisions occur at kinetic energies in the range of tens to several hundred electronvolts. The experiments also demonstrate that production of fragment ions is sensitive to the phase of the main radiofrequency drive voltage at the point when the dc is initiated.     

Generating protein sequence tags by combining cone and conventional collision induced dissociation in a quadrupole time-of-flight mass spectrometer

The goal of proteomics research is to be able to identify and quantify the vast numbers of proteins within an organism or tissue. "Top-down" methods address this goal without the need for proteolytic digestion prior to mass analysis. We report here an approach for top-down protein identification that has been implemented on a commercially available, unmodified Qq-TOF mass spectrometer. Intact protein molecular ions first undergo cone fragmentation in the electrospray inlet. Conventional MS/MS is then performed on a mass selected cone fragment using CID in the Qq interface of the Qq-TOF mass spectrometer to generate a sequence tag through a pseudo-MS3 experiment. Seven proteins varying in molecular weight between 11 and 66 kDa were chosen to demonstrate applicability of method. After the molecular weight of the intact protein was determined, the cone voltage was varied to induce fragmentation. Cone fragment ions were then further dissociated using conventional CID, and the resulting MS/MS spectra were processed and analyzed for sequence tags. Sequence tags were easily identified from a MS/MS spectrum of a cone induced fragment ion both manually and through a de novo sequencing program included in the software associated with the mass spectrometer. Sequence tags were subjected to database searching using the PeptideSearch program of EMBL, and all protein sequence tags gave unambiguous search results. In all cases, sequence tags were found to originate from the n- and/or c-termini of the proteins.     

A two-dimensional quadrupole ion trap mass spectrometer

The use of a linear or two-dimensional (2-D) quadrupole ion trap as a high performance mass spectrometer is demonstrated. Mass analysis is performed by ejecting ions out a slot in one of the rods using the mass selective instability mode of operation. Resonance ejection and excitation are utilized to enhance mass analysis and to allow isolation and activation of ions for MS(n) capability. Improved trapping efficiency and increased ion capacity are observed relative to a three-dimensional (3-D) ion trap with similar mass range. Mass resolution comparable to 3-D traps is readily achieved, including high resolution at slower scan rates, although adequate mechanical tolerance of the trap structure is a requirement. Additional advantages of 2-D over 3-D ion traps are also discussed and demonstrated.     

Scanwave: A new approach to enhancing spectral data on a tandem quadrupole mass spectrometer

A new type of mass analyzer is described, which allows lowresolution axial ion ejection to be obtained from a traveling wave based, stacked ring collision cell. Linking this ejection temporally with the scanning of the second quadrupole of a tandem quadrupole mass spectrometer provides an improvement in sampling duty cycle, which results in significant signal intensity improvements for scanning acquisitions such as product ion spectra. A near 100% storage efficiency is enabled by a split cell design, which allows ion fragmentation and accumulation to be performed in one section of the collision cell whilst previously accumulated ions are simultaneously ejected from the rear of the cell. These characteristics combine to give an m/z-dependent signal gain of 7–20X over a conventional scanning quadrupole for a 1000 Th scan. The ability to swap very rapidly from a non-enhanced mode of operation to an enhanced mode whilst retaining the existing sensitivity, speed, and functionality of a conventional tandem quadrupole mass spectrometer is also described.     

Desorption ionization/tandem mass spectrometry with a caesium ion source and a triple quadrupole mass spectrometer

The coupling of a caesium ion source to a triple quadrupole mass spectrometer is described. The potential of this combination for examining thermally labile, non-volatile molecules, such as thiamine hydrochloride, is examined. Emphasis is placed on the advantages the various scanning modes of tandem mass spectrometry provide in ion structure elucidation and the investigation of desorption ionization mechanisms. Use of the caesium ion source for desorption of neutral molecules which are chemically ionized by an auxiliary gas is demonstrated. This procedure may be especially useful for examining non-volatile, non-ionic samples.     

Effects of target gas in collision-induced dissociation using a double quadrupole mass spectrometer and radiofrequency

Collision-induced dissociation (CID) of polyatomic ions sampled from an rf-powered glow discharge is examined by using three target gases including atomic (Ar and Xe) and molecular species (N2). Collisions with these targets in the first quadrupole of the double quadrupole system result in the loss of discharge species by dissociation, symmetric and asymmetric charge exchange, and scattering, each to varying degrees. These processes are seen to be a function of the relative mass, size... and ionization potentials of the target species, as well as the collision center-of-mass energies. In light of the comparisons, xenon appears to be the best collision target for both CID and charge exchange because of its relatively low ionization potential and high dissociation efficiency of polyatornic species. Evidence for both symmetric and asymmetric charge exchange is presented for Ar and Xe target gases.     

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. A DDC potential is applied across one pair of rods in the quadrupole collision cell of a QqTOF hybrid mass spectrometer to effect fragmentation. In this study, ions derived from a small drug molecule, a model peptide, a small protein, and an oligonucleotide were subjected to the DDC CID method in either an ion trapping or an ion transmission mode (or both). Several key experimental parameters that affect DDC CID results, such as time, voltage, low mass cutoff, and bath gas pressure, are illustrated with protonated leucine enkephalin. The DDC CID dissociation method gives a readily tunable, broadband tool for probing the primary structures of a wide range of analyte ions. The method provides an alternative to the narrow resonance conditions of conventional ion trap CID and it can access more extensive sequential fragmentation, depending upon conditions. The DDC CID approach constitutes a collision analog to infrared multiphoton dissociation (IRMPD).     

Mass spectral fragmentation pathways in nitroadamantanes. A tandem mass spectrometric collisionally induced dissociation study

A collisionally induced dissociation study of adamantane, 1-nitroadamantane, 1,3-dinitroadamantane and 1,3,5,7-tetranitroadamantane was carried out using tandem high-resolution mass spectrometry. Fragmentation pathways of the compounds were determined in the electron impact mode. It was found that the fragmentation of all three nitroadamantanes begins with the consecutive losses of the NO₂ groups followed by fragmentation of the hydrocarbon structure.     

Sulphonium ions: Collision-activated dissociation using fast atom bombardment ionization and a triple quadrupole mass spectrometer

The low-energy collision-activated dissociation of sulphonium cations, including symmetrical trialkyl R³S⁺, dimethylalkyl (CH₃)₂RS⁺, diphenylalkyl Ph₂RS⁺ and cyclic (CH₂)_nS⁺R, has been recorded using fast atom bombardment ionization and a triple quadrupole mass spectrometer. The general trends are easy loss of sulphide to give [R]⁺, except for R ? CH₃, and loss of alkene to give protonated sulphide if β-hydrogens are available. Loss of alkane, generally found in ammonium compounds, is not observed.     

Proposed mechanisms for the fragmentation of doubly allylic alkenamides (tingle compounds) by low energy collisional activation in a triple quadrupole mass spectrometer

Tingle compounds are a class of alkenamides with organoleptic properties that include a numbing or a pins and needles effect that is generally perceived on the lips and in the mouth when consumed. They occur in nature in a number of botanical species. Spilanthol and Pellitorine are important examples of tingle compounds. A number of homologs and analogs were synthesized to study the effect of chain length, double bond location, and amide moiety on the tingle effect. This also provided the opportunity to study the behavior of these compounds in the collision cell of a triple quadrupole mass spectrometer. The doubly allylic 2E,6Z-alkenamides, which made up the largest class studied, fragmented in a characteristic way to produce a distonic radical cation and a cyclopropene cation. Mechanisms for the formation of these ions are proposed. The mechanisms are supported by energy-resolved mass spectrometric data, the analysis of deuterated analogs and homologs that are not doubly allylic, and exact mass measurements. Exceptions to the proposed mechanisms are also presented. These data represent the first attempt to apply mechanistic principles to the product ions observed in the MS/MS spectra of these compounds. The authors believe the results of this study will facilitate the identification of these and similar compounds and contribute to the fundamental understanding of the behavior of alkenamides in the collision cell of a triple quadrupole mass spectrometer.     

A tandem quadrupole/time-of-flight mass spectrometer with a matrix-assisted laser desorption/ionization source: design and performance

A matrix-assisted laser desorption/ionization (MALDI) source has been coupled to a tandem quadrupole/time-of-flight (QqTOF) mass spectrometer by means of a collisional damping interface. Mass resolving power of about 10,000 (FWHM) and accuracy in the range of 10 ppm are observed in both single-MS mode and MS/MS mode. Sub-femtomole sensitivity is obtained in single-MS mode, and a few femtomoles in MS/MS mode. Both peptide mass mapping and collision-induced dissociation (CID) analysis of tryptic peptides can be performed from the same MALDI target. Rapid spectral acquisition (a few seconds per spectrum) can be achieved in both modes, so high throughput protein identification is possible. Some information about fragmentation patterns was obtained from a study of the CID spectra of singly charged peptides from a tryptic digest of E. coli citrate synthase. Reasonably successful automatic sequence prediction (>90%) is possible from the CID spectra of singly charged peptides using the SCIEX Predict Sequence routine. Ion production at pressures near 1 Torr (rather than in vacuum) is found to give reduced metastable fragmentation, particularly for higher mass molecular ions. Copyright 2000 John Wiley & Sons, Ltd.