Final Report

∙ We have succeeded in developing simulation methods that reliably predict performance of ion trap mass spectrometers including the relationship between geometry, electric fields, ion motion, and mass spectra ∙ These procedures have been used to optimize cylindrical ion traps (CITs) including those used in the commercial Griffin Analytical Technologies instruments ∙ We have generalized the simulation program (ITSIM) to allow calculation of ion motion and of mass spectra in 3D electric fields of any arbitrary shape ∙ We have invented the rectilinear ion traps (RIT), a version of linear ion trap which traps an order of magnitude more ions than previous 3D (Paul) ion traps ∙ We have simulated and built arrays of ion traps suited to multiplexed mass analysis and other purposes ∙ Practical applications of our ion traps in miniature mass spectrometers include air monitoring applications (DHS supported) and explosives monitoring experiments (TSA supported) both based on the fundamental DOE-supported work ∙ Applications and simulations of ion motion in the newly commercialized high resolution mass spectrometer (Orbitrap) employed for the understanding of ion motion and its control developed using the ITSIM program ∙ Large inverse KIEs have been discovered in halogen cluster ions and are interesting for their magnitude and mechanistic implications (threshold angular momentum effects on rotational predissociation) ∙ The kinetic method of thermochemical estimation has been extended to quantitative chiral analysis and the methodology has been transferred to the pharmaceutical industry through lectures, discussions and collaborations ∙ The kinetic method has also been successfully applied to the quantatitave analysis of structural isomers, especially isomeric peptides ∙ The serine octamer has been generated by sublimation; this magic-number cluster exists in two isomeric forms and has a strong preference for homochirality. The implications of these and related observations on sprayed serine for the origin of homochirality on earth confirm our work in this are

Sampling of aryldiazonium, anilino, and aryl radicals by membrane introduction mass spectrometry: Thermolysis of aromatic diazoamino compounds

Membrane introduction mass spectrometry (MIMS) is used to sample free radicals generated by thermolysis at atmospheric pressure. This is done by heating the solid sample in a custom-made probe that is fitted with a silicone membrane to allow selective and rapid introduction of the pyrolysates into the ion source of a triple quadrupole mass spectrometer. Phenyldiazonium radical (C6H5N2) and some of its ring-substituted analogs, the methoxy anilino radical CH3OC6H4NH, and aryl radicals are generated by gas phase thermolysis of symmetrical aryl diazoamino compounds (ArNH-N2Ar). The radicals are identified by measurement of their ionization energies (IE) using threshold ionization efficiency data. A linear correlation between the ionization energy of the phenyldiazonium radicals and their Brown σ+ values is observed, and this confirms the formation of these species and validates the applicability of MIMS in sampling these radicals. The ionization energies of the aryldiazonium radicals are estimated as IE (p-CH3O-C6H4N2·), 6.74 ± 0.2 eV; IE (p-CH3-C6H4N2·), 7.72 ± 0.2 eV; IE (C6H5N2·), 7.89 ± 0.2 eV; IE (m-Cl-C6H4N2·), 7.91 ± 0.2 eV; IE (p-F-C6H4N2·), 8.03 ± 0.2 eV; and IE (m-NO2-C6H4N2·), 8.90 = 0.2 eV. The ionization energies of the aryl radicals are estimated as IE (p-CH3O-C6H4·), 7.33 ± 0.2 eV; IE (p-CH3-C6H4·), 8.31 ± 0.2 eV; IE (C6H5·), 8.44 ± 0.2 eV; IE (m-Cl-C6H4·), 8.50 ± 0.2 eV and IE (p-F-C6H4), 8.54 ± 0.2 eV. Also, the ionization energy of the p-methoxyanilino radical (p-CH3O-C6H4NH·) is estimated as 7.63 ± 0.2 eV

C-F and C-C bond activation by transition metals in low energy atomic ion/surface collisions

The transition metal ions, Cr+·, Mo+·, W+· and Re+, abstract one or more fluorine atoms or CmFn groups (m = 1,2; n = 1-5) in collisions with fluorocarbon self-assembled monolayers (F-SAMs). The number of atoms abstracted increases with collision energy, and with W+· and Re+ it is possible to maximize a specific scattered product ion by selecting the appropriate collision energy. The collision energy dependence suggests that dissociation of the products of multiple abstractions is not an important source of any of the observed ion/surface reaction products. The ions W+· and Re+ activate and insert into C-C as well as C-F bonds. In Re+ collisions, products of C-C bond activation are of comparable intensity to the C-F activation products. The reactivity of the ions towards fluorine abstraction is observed to be Cr+· <Mo+· <W+· <Re+. The data are interpreted in terms of reaction at the surface and are rationalized by considering three factors (i) the electronic structures of the ions, (ii) the thermochemistry of fluorine abstraction, and (iii) the degree of orbital overlap of the metal ion and the F-SAM substrate

Covalent chemical modification of self- assembled fluorocarbon monolayers by low- energy CH<SUB>2</SUB>Br<SUB>2</SUB><SUP>+&#183;</SUP> ions: a combined ion/surface scattering and X-ray photoelectron spectroscopic investigation

Specific covalent chemical modification at the outermost atomic layers of fluorinated self-assembled monolayers (F-SAMs) on gold is achieved by bombardment with low-energy polyatomic ions (&lt;100 eV). The projectile ion CH2Br2+&#183; (m/z 172), mass and energy selected using a hybrid ion/surface scattering mass spectrometer and scattered from the F-SAM surface, CF3(CF2)7(CH2)2-S-Au, undergoes ion/surface reactions evident from the nature of the scattered ions, CH2F+ (m/z 33), CHBrF+ (m/z 111), and CF2Br+ (m/z 129). The chemical transformation of the reactive F-SAM surface was independently monitored by in situ chemical sputtering with the projectile Xe+&#183;. Representative species sputtered from the modified surface include CF2Br+, an indicator of terminal CF3 to CF2Br conversion. X-ray photoelectron spectroscopy (XPS) was used to confirm the presence of organic bromine at the surface; Br (3P3/2) and Br (3P&#189;) peaks were present at binding energies of 182 and 190 eV, respectively. XPS analysis also revealed increased surface modification at higher collision energies in these reactive ion bombardment experiments, as exemplified by the increased hydrocarbon/fluorocarbon peak ratio in the C(1s) region and incorporation of oxygen in the surface seen in the observation of an O(1s) peak

Atmospheric Pressure Thermal Dissociation of Phospho- and Sulfopeptides

Several phospho- and sulfopeptides were subjected to atmospheric pressure thermal dissociation (APTD), which was effected by passing peptide ions generated by electrosonic spray ionization (ESSI) through a heated coiled metal tube. Sequence informative fragment ions including a-, b-, c-, and y-types of ions were observed with increased relative intensities under APTD compared with collision-induced dissociation (CID), performed inside the ion trap. A certain degree of preservation of phosphate and sulfate ester moieties was observed for some fragments ions under APTD. The neutral fragments generated outside the mass spectrometer were further analyzed via on-line corona discharge to provide rich and complementary sequence information to that provided by the fragment ions directly obtained from APTD, although complete losses of the modification groups were noted. Improved primary sequence information for phospho- and sulfopeptides was typically obtained by analyzing both ionic and neutral fragments from APTD compared with fragment ions from CID alone. Localization of the modification sites of phospho- and sulfopeptides was achieved by combining the structural information acquired from APTD and CID

Direct analysis of camptothecin from Nothapodytes nimmoniana by desorption electrospray ionization mass spectrometry (DESI-MS)

Desorption electrospray ionization was employed for fast and direct ambient detection of the anti-tumor drug, camptothecin, and its derivative, 9-methoxycamptothecin in Nothapodytes nimmoniana. Different parts of the plant such as leaves, stems and bark were examined. The ion intensities suggest that the concentration in bark is higher than that in the leaves and stems. The method does not require any sample preparation or preseparation. The identity of the alkaloids was further confirmed by tandem mass spectrometry

Spatial Segmentation and Feature Selection for Desi Imaging Mass Spectrometry Data with Spatially-Aware Sparse Clustering.

Recent experimental advances in matrix-assisted laser desorption/ionization (MALDI) and desorption electrospray ionization (DESI) have demonstrated the usefulness of these technologies in the molecular imaging of biological samples. However, development of computational methods for the statistical interpretation and analysis of the chemical differences present in the distinct regions of these samples is still a major challenge. In this poster, we propose statistically-minded methods and computational tools for analyzing DESI imaging experiments. Specifically, we present techniques for signal processing and unsupervised multivariate image segmentation, which are also applicable to other imaging mass spectrometry (IMS) methods such as MALDI

Mass Spectrometry in the Home and Garden

Identification of active components in a variety of chemical products used directly by consumers is described at both trace and bulk levels using mass spectrometry. The combination of external ambient ionization with a portable mass spectrometer capable of tandem mass spectrometry provides high chemical specificity and sensitivity as well as allowing on-site monitoring. These experiments were done using a custom-built portable ion trap mass spectrometer in combination with the ambient ionization methods of paper spray, leaf spray, and low temperature plasma ionization. Bactericides, garden chemicals, air fresheners, and other products were examined. Herbicide applied to suburban lawns was detected in situ on single leaves 5 d after application

Rephasing Ion Packets in the Orbitrap Mass Analyzer to Improve Resolution and Peak Shape

A method is described to improve resolution and peak shape in the Orbitrap under certain experimental conditions. In these experiments, an asymmetric anharmonic axial potential was first produced in the Orbitrap by detuning the voltage on the compensator electrode, which results in broad and multiply split mass spectral peaks. An AC waveform applied to the outer electrode, 180° out of phase with ion axial motion and resonant with the frequency of ion axial motion, caused ions of a given m/z to be de-excited to the equator (z = 0) and then immediately re-excited. This process, termed “rephasing,” leaves the ion packet with a narrower axial spatial extent and frequency distribution. For example, when the Orbitrap axial potential is thus anharmonically de-tuned, a resolution of 124,000 to 171,000 is obtained, a 2- to 3-fold improvement over the resolution of 40,000 to 60,000 without rephasing, at 10 ng/μL reserpine concentration. Such a rephasing capability may ultimately prove useful in implementing tandem mass spectrometry (MS/MS) in the Orbitrap, bringing the Orbitrap\u27s high mass accuracy and resolution to bear on both the precursor and product ions in the same MS/MS scan and making available the collision energy regime of the Orbitrap, ∼1500 eV

Rephasing Ion Packets in the Orbitrap Mass Analyzer to Improve Resolution and Peak Shape

A method is described to improve resolution and peak shape in the Orbitrap under certain experimental conditions. In these experiments, an asymmetric anharmonic axial potential was first produced in the Orbitrap by detuning the voltage on the compensator electrode, which results in broad and multiply split mass spectral peaks. An AC waveform applied to the outer electrode, 180° out of phase with ion axial motion and resonant with the frequency of ion axial motion, caused ions of a given m/z to be de-excited to the equator (z = 0) and then immediately re-excited. This process, termed “rephasing,” leaves the ion packet with a narrower axial spatial extent and frequency distribution. For example, when the Orbitrap axial potential is thus anharmonically de-tuned, a resolution of 124,000 to 171,000 is obtained, a 2- to 3-fold improvement over the resolution of 40,000 to 60,000 without rephasing, at 10 ng/μL reserpine concentration. Such a rephasing capability may ultimately prove useful in implementing tandem mass spectrometry (MS/MS) in the Orbitrap, bringing the Orbitrap\u27s high mass accuracy and resolution to bear on both the precursor and product ions in the same MS/MS scan and making available the collision energy regime of the Orbitrap, ∼1500 eV