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We report ion-mobility measurements with a modified triple quadrupole mass spectrometer fitted with an ion molecule reactor (IMR) designed to investigate ion molecule reactivity in organic mass spectrometry. Functionalized pentacene ions, which are generally unreactive were chosen for study to decouple drift/diffusion effects from reactivity (including clustering). The IMR is equipped with a variable axial electrostatic drift field (ADF) and is able to trap ions. These capabilities were successfully employed in the measurement of ion mobilities in different modes of IMR operation. Theoretical modeling of the drift dynamics and the special localization of the large ion packet was successfully implemented. The contribution of the quadrupole RF field to the drift dynamics also was taken into consideration.

In this study, a new design for electrospray ionization ion mobility spectrometry (ESI-IMS) was developed. This design has two important differences in comparison to the present ESI-IMS systems. First, a few centimeters of the cell comprising the electrospray needle was located outside of the oven used for heating the IMS cell. This modification prevents prespray solvent evaporation problems such as needle clogging and disturbance of the electrospray process. Second, in addition to the drift gas, a counterflow of a heated gas (desolvation gas) was used between the counter electrode and the ion gate to speed up the desolvation process (Hill, H. H., Jr. Anal. Chem. 1998, 70, 4929-4938). This modification increased the solvent evaporation and resulted in decreasing the drift time, increasing the peak intensity and increasing the resolving power (RP) or enhancing the resolution for separation of two adjacent ion peaks. In this work, the ion mobility spectra of different compounds including ethion, malathion, metalaxyl, fenamifos, methylamine, triethylamine, tributhylamine, codeine, and morphine were obtained to confirm enhancing of the resolving power of the ion peaks by using the desolvation gas. Furthermore, the method has also been applied to obtain the figures of merit for ethion as a test compound. The linear dynamic range for ethion was in the range 50-1000 g/L with a limit of quantification of the 50 g/L.

Electrospray mass spectrometry (ESI–MS) gas phase methods were extended by the addition of structural information by ion mobility spectrometry. In a first attempt a conventional Electrospray ionization tandem mass spectrometer (ESI–MS/MS) was used to determine collision cross sections for aniline-H+ and derivatives as well as for isobaric ions by applying retarding potentials at the exit of the collision cell. Literature values are reproduced, but the resolution is too low to achieve separation of analyte ions according to their collision cross sections. A literature evaluation of different ion mobility setups was made followed by successful construction of a high pressure high field mobility cell fitting to the entry of a TSQ 700 triplequad ESI–MS. The complete hardware setup including electronic supplies was developed as well as driver software and spectra workup routines for different measurement modes. Test measurements were performed with different analyte systems showing good performance and separation capabilities. A resolution factor of 50 (td/tfwhm) was achieved as well as base line separation at the level of 6% difference in collision cross section. Literature values for o-/m-/p-phthalic acid dimethylesters are well reproduced as well as for aniline-H+ and derivatives. Ion mobility measurements on different catalytic systems and organic compounds were performed. In most cases the application of ion mobility measurements was new. Collision cross sections were measured of most of these species but however in some cases the designated separation could not be achieved. Based on these (negative) results improvement proposals are made. On serine octamer clusters up to 8 different isobaric species were detected right at the border level of successful desolvation. The species could be assigned successfully to calculated literature structures. The detection of multiple species in this case is in VI Abstract contrast published results on a different measurement setup. Investigations on ethylene polymerization by access over quenching with DCC were made. A set of model compounds was used to measure the collision cross sections of differently branched isomers. The measurements and mobility calculations are in good agreement. Size selected Branching ratios were delimited by peak form integration. In another project reactivity studies on the ionic Ir(PHOX) complex, an asymmetrical hydrogenation catalyst, were performed using mass spectrometry gas–phase reactions. Mechanistical pathways could be explored by related complexes. The reaction indicate that the hydrogenation proceeds by an IrI / IrIII rather than by the previously proposed IrIII / IrV polyhydride route. Additionally a new, faster method for CID threshold measurements and improvements thereof in terms of energy distribution and reproducibility was introduced. The method is currently used for investigations on a large set of CuI (BOX) and CuI (PyBOX) complexes to measure absolute metal–ligand binding constants.

We describe the successful coupling of CEC and capillary HPLC with the recently developed atmospheric-pressure laser ionization (APLI) method. APLI is suitable for selectively and sensitively ionizing nonpolar aromatic compounds at ambient pressure for subsequent mass-selective detection. The polycyclic aromatic hydrocarbons used as analytes are first separated either by CEC on a silica-based monolithic column or by capillary HPLC. The eluent, along with a sheath flow, is volatilized by microelectrospray and then selectively ionized by excimer laser (KrF*) radiation via two-photon excitation. A QTOF-MS is used as mass-selective detector. This interface combination makes soft ionization of thermally labile nonpolar aromatic analytes possible.

A number of carboxylate anions spanning a mass range of 87-253 amu (pyruvate, oxalate, malonate, maleate, succinate, malate, tartarate, glutarate, adipate, phthalate, citrate, gluconate, 1,2,4-benzenetricarboxylate, and 1,2,4,5-benzenetetracarboxylate) were investigated using electrospray ionization ion mobility spectrometry. Measured ion mobilities demonstrated a high correlation between mass and mobility in both N2 and CO2 drift gases. Such a strong mass-mobility correlation among structurally dissimilar ions suggests that the carboxylate functional group that these ions have in common is the source of the correlation. Computational analysis was performed to determine the most stable conformation of the studied carboxylate anions in the gas phase under the current experimental conditions. This analysis indicated that the most stable conformations for multicarboxylate anions included intramolecular hydrogen-bonded ring structures formed between the carboxylate group and the neutral carboxyl group. The carboxylate anions that form ring confirmations generally show higher ion mobility values than those that form extended conformations. This is the first observation of intramolecular hydrogen-bonded ring conformation of carboxylate anions in the gas phase at atmospheric pressure.

Chemical standards for positive ion mode electrospray ionization ion mobility spectrometry/mass spectrometry (ESI(+)-IMS/MS) are suggested. The low clustering tendency of tetraalkylammonium halides makes them ideal chemical standards for ESI(+)-IMS/MS. A homologous series of these compounds forms a useful external standard for instrument testing and resolution calibration of an IMS instrument. Selected homologues or a mixture of tetraalkylammonium halides can be used as mobility standards in the analytical runs. Absolute and relative reduced mobilities were calculated for C2C8, C10 and C12 tetraalkylammonium halides. Absolute reduced mobilities in nitrogen were 1.88, 1.56, 1.33, 1.15, 1.02, 0.92, 0.84, 0.73, and 0.67 cm2 V-1 s-1, for C2C8, C10 and C12 tetraalkylammonium halides, respectively. Relative reduced mobilities (relative to 2,6-di-tert-butylpyridine) for the same compounds were 1.20, 1.00, 0.855, 0.743, 0.658, 0.59, 0.54, 0.47, and 0.43, respectively. Copyright © 2005 John Wiley & Sons, Ltd.

A series of isobaric disaccharide-alditols, four derived from O-linked glycoproteins, and select trisaccharides were rapidly resolved using tandem high resolution atmospheric pressure ion-mobility time-of-flight mass spectrometry. Electrospray ionization was used to create the gas-phase sodium adducts of each carbohydrate. Using this technique it was possible to separate up to three isobaric disaccharide alditols and three trisaccharides in the gas phase. Reduced mobility values and experimentally determined ion-neutral cross sections are reported for each sodium-carbohydrate complex. These studies demonstrated that ion mobility separations at atmospheric pressure can provide a high-resolution dimension for analysis of carbohydrate ions that is complementary to traditional mass spectral (m/z) ion analysis. Combining these independent principles for separation of ions provides a powerful new bioanalytical tool for the identification of isomeric carbohydrates.

We present a design for a low-cost ion mobility spectrometer that can be built using the equipment on hand in many electronics-oriented undergraduate laboratories. The construction of this system is based upon the use of printed circuit boards and does not require the specialized drift and sheath gases, vacuum pumps, heater assemblies, high voltage pulsers, or precision pumps that are characteristic of the systems generally reported in the literature. We demonstrate the system in the separation of ions of methanol and water in air. Despite the low cost of this system it has a performance comparable to more complex systems, with a sensitivity of approximately 100 ppm for the protein cytochrome c. This system is suitable for use as an electronics or signal-processing project, or even a biotechnology demonstration. ©2004 Am

As part of an ongoing effort to explore the utility of high-resolution electrospray ionization ion mobility spectrometry (ESI-IMS) for the detection and identification of organic molecules on other planetary bodies, pursuant to NASA objectives, the reduced ion mobilities of 14 amino acids that have been identified in meteoritic material were determined in both N2 and CO2 drift gases. A (12,4) hard core potential model of the ion-neutral interaction was applied to a combined data set of amino acid mobilities from the present work (abiotic) and an earlier investigation of twenty common biotic amino acids (Beegle, L. W.; Kanik, I.; Matz, L.; Hill, H. H. Anal. Chem. 2001, 73, 3028-3034). The model was used to investigate the protonated amino acid mass-mobility correlation to extract details of the ion-neutral interaction and to gain insight into the structural details of these ions.