Reactive Tandem Ion Mobility Spectrometry with Electric Field

Subscriber access provided by UNIV OF LOUISIANA

Article

REACTIVE TANDEM ION MOBILITY SPECTROMETRY WITH ELECTRIC FIELD FRAGMENTATION OF ALCOHOLS AT AMBIENT PRESSURE Hossein Shokri, Maika Vuki, Ben Gardner, Hsein-Chi W Niu, Umesh Chiluwal, Bhupendra K Gurung, David B Emery, and Gary A Eiceman Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.9b01057 • Publication Date (Web): 10 Apr 2019 Downloaded from http://pubs.acs.org on April 13, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

REACTIVE TANDEM ION MOBILITY SPECTROMETRY WITH ELECTRIC FIELD FRAGMENTATION OF ALCOHOLS AT AMBIENT PRESSURE

Hossein Shokri, Maika Vuki,1 Ben Gardner,2 Hsein-Chi Niu,2 Umesh Chiluwal, Bhupendra K. Gurung, David B. Emery, and Gary A. Eiceman Department of Chemistry and Biochemistry New Mexico State University Las Cruces, NM 88003 1Chemistry

Department

University of Guam Mangilao, Guam 96913 2Collins

Aerospace, Pomona, CA 91767

March 28, 2019

ACS Paragon Plus Environment

Analytical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT A tandem ion mobility spectrometer at ambient pressure with a reactive stage produced fragment ions by water elimination from protonated monomers of alcohols with carbon numbers three to nine. Protonated monomers of individual alcohols were mobility isolated in a first drift region and were fragmented to carbocations at 64 to 128 Td and 45 to 89˚C. Precursor and fragment ions were mobility characterized in a second drift region. Enthalpies for fragmentation of ROH2+ to primary carbocations were calculated as 76 to 97 kJ/mole and enthalpies for subsequent charge migration to 2˚ carbocations were -49 to -58 kJ/mole. Plots of drift times for pairs of protonated monomer and fragment ions from alcohols, esters, alkanes, and aldehydes produced distinctive trend lines attributed to fragmentation paths characteristic of chemical class. Specific combinations of drift times for fragments and precursor ions provide additional chemical information for spectral interpretation in ion mobility spectrometry.

Key Words: Tandem, Ion Mobility Spectrometry, Reactive, Alcohols


Page 2 of 24

Page 3 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Ion mobility spectrometry (IMS) has been a selective detector for substances of military or security significance for 30+ years with hand-held or benchtop analyzers operated at ambient pressure in purified air.1,2 Although drift tubes in these analyzers are comparatively low resolving power, selectivity of response is provided by preferential ionization and mobility characterization of ions derived from target analytes. Soft chemical ionization and limited resolving power yield simple spectral patterns without structural detail as found with electron ionization mass spectra3 or collision induced dissociation in tandem mass spectrometry (MS).4 Consequently, while used as a sensitive detector, mobility spectrometers have been historically unsuitable for molecular identification of substances. The existence of some structural information in mobility spectra was suggested from the classification of spectra, even with unfamiliar compounds, by chemical class using artificial neural networks (ANNs).5-7 Classification had been associated with a specific narrow region of drift times thought to contain fragment ions generated in-source with beta emission. Performance of ANNs for a wide range of chemical classes suggested indirectly that fragmentation of gas phase ions in air was a general process, though at low abundances near baseline noise. Intensities of fragment ions could be increased significantly by increasing the energies of precursor ions, such as protonated monomers, using thermal sources or electric fields as demonstrated with esters and alcohols.8,9 Protonated monomers of alcohols have been fragmented using a range of techniques including chemical ionization mass spectrometry (MS),10,11 collision induced dissociation in tandem MS,12 and ion flow drift tube-MS,13 each with water elimination to carbocations as the initial reaction. Ions of alcohols also have been fragmented in IMS under thermal conditions.14 Further increases in ion energy by increased ratios of electric field strength (E) to number density (N) with proton transfer-mass spectrometry (PTR-MS), resulted in further fragmentation of carbocations with loss of C2H4 and later H2.15 Methods to fragment ions in electric fields have been described for IMS drift tubes16-18 and were implemented recently with a tandem ion mobility spectrometer for decomposition of negative ions of explosives and interferences at E/N of 120 Td.19 Mobility selection of ions before decomposition provided a direct association between the precursor ion and electric field decomposed ions, increasing selectivity of response and spectral clarity on an uncluttered baseline. Chloride adducts were decomposed through substitution reactions, hydrogen abstractions, and adduct dissociations.19



In the present work, protonated monomers of alcohols are fragmented in a set of wire grids over a range of gas temperatures and electric field strengths in air using a low resolving power drift tube. Comparisons of trends in plots of drift times of precursor and fragment ions with several other chemical families including esters, alkanes, and aldehydes suggest reactive tandem IMS may provide new capabilities in chemical measurements using IMS methods at ambient pressure. EXPERIMENTAL Instrumentation A tandem ion mobility spectrometer shown in Figure 1 was built in-house with stainless steel drift rings (1.1 mm thick x 14.7 mm ID x 25.6 cm OD) and virgin Teflon insulators (1.9 mm thick x 14.7 mm ID x 25.6 cm OD). The ion source was a planar stainless steel disk (14.4 mm OD) plated with 6 mCi 63Ni. Drift tube dimensions included a 41.8 mm reaction region, a 21.4 mm long first drift region with ion shutter 1 and a 22.0 mm long second drift region with ion shutter 2. Ion shutters were Tyndall Powell type with metal etched grids separated by a 0.05 mm thick Teflon insulator. Each grid was 0.1 mm thick x 13.0 mm ID with wires inter-digitated at 0.63 mm between centers. Ion shutters were controlled using in-house electronics where a master clock established a time base for data acquisition and ion shutters 1 and 2 were both referenced to this time base. Pulse width for ion shutters was 200 µs. A uniform electric field of ~293 V/cm in the drift tube was provided by a high voltage supply of ~2.7 kV DC. An aperture grid was located at 0.7 mm from the Faraday plate detector. Electric fields for ion fragmentation were formed between two metal etched grids placed 1.2 mm from ion shutter 2. Ion fragmentation occurred when Grid 2 (Fig. 1) was provided a ~3.4 MHz sinusoidal waveform on a DC voltage of 754 V from a Modular Intelligent Power Sources (MIPS), version 2, from GAA Custom Engineering, LLC (Benton City, WA). Amplifier and high voltage power supplies were based on in-house designs. Spectra were acquired using a 18 bit interface card PCI-6281 DAQ (National Instruments, Austin, TX) and Lab View software (Linear 2018 version 2.0) referenced to the master clock for operation of both ion shutters. The drift tube was placed in an oven for uniform heating throughout the drift tube (±3˚C). Drift gas of 220 ml/min was air purified using 5Å molecular sieve providing 1 to 5 ppm moisture. The tandem IMS drift tube was connected to a model 5890 series II gas chromatograph (Hewlett-Packard, Co., Avondale, PA) for sample pre-fractionation. The gas chromatograph was equipped with a split-splitless injector, 10 meter long x 0.18 mm ID RTX-200 capillary column (Restek


Page 4 of 24

Page 5 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Corporation, Bellefonte, PA), and a 56 cm long x 6 mm OD x 3 mm ID stainless steel tube interface at 150°C containing a 62 cm HT5 (AQ) (0.32 mm ID, SGE Analytical Science) capillary column. A drift tube without ion shutters, for full ion transmission, was attached to the capillary inlet of a model 2010 mass spectrometer (Shimadzu Corp., Kyoto, Japan). The drift tube was comprised of Teflon ring insulators and stainless steel drift rings as described20 and was equipped with a 10 mCi 63Ni ion source. Total drift tube length was 11.43 cm with drift field of 300 V/cm. A wire grid pair for electric field fragmentation was placed in the drift tube 6 cm from the capillary inlet. Purified air at 1.2 L/min was added to the drift tube near the capillary interface of the mass spectrometer with 1 L/min drawn into the mass spectrometer and 200 ml/min passed counter-flow through the drift tube, venting through the 63Ni

ion source. The drift tube was attached to a model 5890 series II gas chromatograph (Hewlett-

Packard, Co., Avondale, PA) as described above for the tandem drift tube. Chemicals and Reagents All chemicals were obtained at more than 97% purity from Sigma-Aldrich Chemical Co. (Milwaukee, WI) and include 2,6-Di-tert-butylpyridine, 1-propanol, isobutanol, 1-butanol, 2-butanol, 1-pentanol, 1hexanol, cyclohexanol, 1-heptanol, 1-octanol, and 1-nonanol. Dichloromethane (99.7% purity) from Alfa Aesar (Tewksbury, MA) was used for preparation of solutions of individual alcohols at 100 ng/µL. Procedures GC Analyses- Injection volumes were 1 µL with 30 second purge off in split-less mode. Injection port temperature was 2000 and oven temperature program was 100°C to 250°C at 20°C/min. Mobility spectra were obtained during elution of an alcohol, well-separated from the solvent peak. Collection of mobility spectra- Mobility spectra were obtained in four modes for operating the ion shutters and wire grid pair for fragmentation: (a) Mode 1, ion shutter 1 is active with both ion shutter 2 and the wire grid pair are inactive. (b) Mode 2, both ion shutters are active and a mobility peak of interest is isolated using a delay of ion shutter 2 from ion shutter 1. The wire grid pair is inactive. (c) Mode 3 a peak is mobility isolated as in Mode 2 and the wire grid pair is active. (d) Mode 4 is the same as Mode 1 and the wire grid pair is active. Every alcohol sample was measured using each of these four modes at 45, 58, 67, and 89°C. In Modes 3 and 4, waveform amplitude was applied in six steps from 13.1 to 23.0 kV/cm on Grid 2. In drift tubemass spectrometer studies, mixtures of alcohols were injected with a GC temperature ramp from 30 to



200˚C at 5˚C/min with the mass spectrometer scanning from 35 to 500 Da every 1.8 s. Data sets were collected with the wire grid pair inactive as a control and with the wire grid pair active.

Computational Modeling Enthalpies for individual reactions from the dehydration and fragmentation of protonated monomers of alcohols were calculated using Spartan 10 (Wavefunction, Inc., Irving, CA ) using density functional theory and the 6-311+G(d,p) basis set. Enthalpy values were computed for step-wise dehydration of MOH2+(H2O)n from n=3 to 2, n=2 to 1, and n=1 to 0. Enthalpies were determined also for water elimination from MOH2+ to a primary carbocation and for a last step of charge and hydrogen migration to a secondary carbocations (except for iso-butanol, a tertiary carbocation and cyclohexanol and 2butanol, both secondary carbocations).

RESULTS AND DISCUSSION Mobility spectra of alcohols in a single drift region Ion mobility spectra for three primary alcohols are shown in Figure 2 (dashed line) from GC/IMS analysis of individual solutions and combined drift regions of the tandem drift tube (Fig. 1). Electric fields in ion shutter 2 and the wire grid pair were inactive (Mode 1). Spectra without alcohol vapor contained only a single peak at 4.95 ms drift time at 67°C (reduced mobility coefficient (Ko) of 2.08 cm2/Vs) with 1.75 ppm moisture in purified air. This peak or reactant ion peak (RIP)21 is a hydrated proton (H+(H2O)n) with calculated distributions of n=2,5.0%; n=3, 88.2%; and n=4, 6.8%.22 Intensity of the RIP decreased during chromatographic elution of an alcohol yielding protonated monomers (ROH2+(H2O)n) and proton bound dimers (ROH)2H+) whose intensity was dynamically established by vapor concentrations of sample in the ion source. Amounts of sample were chosen so vapor concentrations in the ion source did not exceed 1 to 3 mg/m3, or 80% depletion of RIP intensity. Values of Ko for ions of alcohols were determined using a chemical standard, 2,6 di-t-butyl pyridine, and are shown in Table 1 matching favorably with literature values.23-24 Proton bound trimers of alcohols, seen at low temperatures,25 were not observed at temperatures in these measurements. Performance of this tandem drift tube was governed by small dimensions, a design goal of the research program. Resolving power (td/w) for peak width at baseline


Page 6 of 24

Page 7 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(w) ranged from 12 to 14 for 1-propanol to 1-pentanol and for peak width at half height ranged from 28 to 31. Signal to noise averaged 70 for the RIP background and 58 to 67 for 1-propanol to 1-pentanol. Electric field fragmentation of all ions (Mode 4)- When ions were heated at 120 Td by an electric field of 22.5 kV/cm in the wire grid pair, intensities for protonated monomers were decreased with simultaneous appearance of a peak at drift times between the RIP and the protonated monomer (Figure 2, solid lines). Drift times for these new ions were, for example, 4.71 ms for 1-pentanol, 5.24 ms for 1heptanol and 5.87 ms for 1-nonanol. Values of Ko for these ions (corrected for formation roughly midway in the drift region) are shown in Table 1 and suggested ion masses larger than RIP and smaller than protonated monomers. Intensities of these ions were proportional to electric field strength in the wire grid pair (see Fragmentation Efficiency below). Mass Analysis of Ions- Mass analysis of ions without electric field fragmentation in the drift tube-mass spectrometer showed proton bound dimers, protonated monomers, and carbocations, generated thermally14 and, perhaps, in the vacuum interface. An example is given in Supporting Information (Figure S1, A) where 1-nonanol at 60˚C showed 289 Da ((ROH)2H+) 163 Da (ROH2+) and 127 Da (C9H19+). When the electric field in the wire gird pair is increased to 168 Td, this carbocation becomes the base peak (Fig. S1, B) with loss of protonated monomer. The carbocation C9H19+ arises from ROH2+ ------> H2O + C9H19+ matched findings from IMS-MS14, PT-MS15, and DMS.9 Since protonated monomer, when dehydrated (i.e., ROH2+), undergoes fragmentation,14 ROH2+(H2O)n with n= 3 in the tandem drift tube should be preceded by dehydration (hydrates of protonated monomer were not observed in mass spectra presumably from ion heating in the vacuum interface). Carbocations were identified by mass analysis for all other alcohols in Table 1. Although intensities for proton bound dimers in spectra (Figure 2) were unchanged at 120 Td, within measurement error, increases of only 48 Td (to 168 Td) resulted in significant decreases in peak intensities (e.g., 1-nonanol in Fig. S1, B). Thus, the enthalpies of 125 to 138 kJ/mole, for dissociation of proton bound dimers of alcohols,26 are bracketed roughly between field strengths of 120 to 168 Td. In planar structures for fragmentation, complete dissociation of proton bound dimers of alcohols was observed near 120 Td9 suggesting lessened efficiency with wire grid pairs compared to planar structures. In addition to the expected water elimination for electric field fragmentation of 1-hexanol (85 Da, C6H13+ produced from loss of H2O), close inspection of the baseline (Fig. S1, C) showed ion intensities well above background for 57 Da (C5H11+ produced from loss of H2O and C2H4) and 43 Da (C3H7+ produced from loss of H2O and C3H6). These findings were consistent with PT-MS findings and demonstrate that



additional fragmentation in the tandem drift tube may occur at ambient pressure when electric fields increased above the present 120 Td limit. While measurements of all ions in Mode 4 and the drift tube mass spectrometer can provide a broad measure of decomposition, mobility selection of an ion should improve confidence in linking precursor ions to fragment ions and may yield fragment ion spectra to aid assignment of spectra to chemical class using field fragmentation, rather than in-source fragmentation.57

Tandem IMS with Mobility Isolated Protonated Monomers. Mobility isolation of Ions (Mode 2)- In mobility selection of ions, ion shutter 2 is synchronized and delayed from ion shutter 1 to isolate a peak in the first, 21.4 mm long, drift region (Fig. 1) with subsequent mobility analysis of ions in a second, 22.0 mm long, drift region. In the absence of electric field fragmentation (Mode 2), mobility selected spectra were comprised of protonated monomers only (Figs. 3 and 4, dashed lines), lacking RIP or proton bound dimers. Resolving power (FWHM) of 36 for 1pentanol was the same, within experimental error, to the longer drift region (Mode 1) and the same ion identities from matching Ko values. Electric Field Fragmentation of Mobility Selected Ions (Mode 3)- When mobility isolated ions were heated in the wire grid pair with E/N at 128 Td, fragment ions appeared with loss of intensity of the protonated monomers (solid lines, Figures 3 and 4). Single fragment ions in each spectrum paralleled findings of Mode 4 and Ko values compared favorably for carbocations (Table 1). The absence of fragment ions with still lower drift times suggests that energy delivered by electric field fragmentation at 128 Td was insufficient for further fragmentation observed in thermal decomposition,13 field fragmentation14 and combined thermal-field fragmentation.9 While comparisons between these findings and others are qualitatively favorable, differences in residence times and complex potential contours in the wire grid pair19 limit quantitative comparisons. Computational values for ion fragmentation were undertaken to provide estimates of reaction energies within the wire grid pair of the reactive tandem drift tube. Calculations on Reaction Enthalpies and Ion Energies Fragmentation of isobutanol (2-methyl-1-propanol) was proposed to proceed through ROH2+ but not hydrated forms14 and general for other alcohols suggests that waters of hydration should be removed in the small tandem drift tube within the wire grid pair at 120Td, prior to on-set of fragmentation. Enthalpy values to dehydrate ROH2+(H2O)3 to ROH2+ show a stepwise increase in energy (Table 2) and


Page 8 of 24

Page 9 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


enthalpies to remove n=3 and n=2 are comparable with stepwise hydrations of a proton.22 The slight increase in enthalpy for the change n=1 to n=0 is also consistent with removal of the first water of hydration which is correctly the dissociation of a heterogeneous proton bound dimer, i.e, ROH·H+·H2O. Water loss from the asymmetric bond RO∙∙∙∙∙H+∙∙∙∙OH2 at ~100 kJ/mol is only 20 to 30 kJ/mol greater than loss of a second or third water of hydration. Trends in enthalpy to form a primary carbocation decreases with increased carbon number (Supporting Information, Fig. S2, A) and can be attributed to inductive stabilization from R. Enthalpy for hydrogen or charge migration to form a secondary carbocation (Supporting Information, Fig. S2, B) becomes more favorable with increased carbon chain length, also attributed to inductive stabilization. The energy needed to dehydrate and fragment protonated monomers from ROH2+(H2O)3 to CnH2n+1+ ranges from 344 kJ/mol for 1-propanol to 320 kJ/mol for 1-nonanol and was 1-hexanol > 1-heptanol > 1-octanol > 1-butanol > 1nonanol > 1-propanol. Similarly intercepts (all negative for E/N= 0Td) from linear regression increased in the order 1-pentanol < 1-hexanol < 1-butanol < 1-heptanol < 1-octanol < 1-nonanol < 1-propanol. These


Page 11 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


trends demonstrate maximum fragmentation (at a given E/N) with 5 to 7 carbon numbers and decreased efficiency with lower and higher carbon numbers. The relative positions of plots in Fig. 6 (also, Table S2, Supporting Information) do not follow ion mass with decreased efficiency of fragmentation at mass extremes (3,4, 8 and 9 carbon number). The apparent maximum with carbon numbers 5 and 6 suggest two or more opposing influences on efficiency fragmentation. One might include heat capacity of ions (low mass ions favored) with increased efficiency with small ions which would be off-set by poor inductive stabilization of carbocations (large mass ions favored). Large ions might be favored by stabilization energy off-set by large energy to heat the ions. Finally, compounds forming secondary or tertiary carbocations directly (cyclohexanol, isobutanol, and 2-butanol) seem preferred over equivalent carbon number primary alcohols. Critically, the E/N to achieve a threshold of 10% fragmentation to carbocation increased (in Td) in the pattern as 68.28, 1-heptanol; 69.74, 1-octanol; 71.53, 1-pentanol; 74.76, 1-hexanol; 83.26, 1-nonanol; 86.14, 1butanol; and 128.91, 1-propanol. Values for other alcohols were 57.19, cyclohexanol; 71.62, 2-butanol; and 75.18, iso-butanol. This patterns are more complex than those observed for acetates and esters where ion mass seemed to govern relative efficiency of fragmentation.8 CONCLUSIONS Reactive tandem ion mobility spectrometry can provide additional features in mobility spectra concerning a substance, from the protonated monomer, through the fragmentation of mobility selected ions and subsequent mobility analysis of fragment ions. In the instances of protonated monomers of alcohols, elimination of water is a characteristic fragmentation pathway providing trend lines which are easily distinguished from esters, alkanes, and aldehydes. Comparisons of pairs of drift times for precursor ions and fragment ions with trend lines for particular chemical classes provide content, in the interpretation of ion mobility spectra, beyond the commonly available Ko values only. The sophistication of this content and broad analytical value may be enhanced with ions produced from second and third fragmentation paths at higher E/N used in these studies. The findings suggest that reactive tandem mobility spectrometers may enhance the analytical value of IMS measurements and establish foundations for molecular identification.



ACKNOWLEDGEMENT This research was funded by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), through an AFRL contract. All statements of fact, opinion or conclusions contained herein are those of the authors and should not be construed as representing the official views or policies of IARPA, the ODNI, or the U.S. Government. The Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright annotation thereon. We gratefully acknowledge conversations with Dr. J.A. Stone, Queens University Kingston Ontario Canada on computational modeling and chemistry of gas phase ions.

REFERENCES (1)

Karpas, Z. Ion Mobility Spectrometry: A Tool in the War against Terror. Bull. Isr. Chem. Soc. 2009, No. 24, 26–31.

(2)

Sferopoulos, R. A Review of Chemical Warfare Agent ( CWA ) Detector Technologies and Commercial-Off-The-Shelf Items. Aust. Gov. Dep. Def. 2009, 98.

(3)

Interpretation of Mass Spectra, 4th Ed. (McLafferty, Fred W.; Turecek, Frantisek). J. Chem. Educ. 1994, 71 (2), A54.

(4)

McLuckey, S. A.; Goeringer, D. E. Slow Heating Methods in Tandem Mass Spectrometry. J. Mass Spectrom. 1997, 32 (5), 461–474.

(5)

Bell, S.; Nazarov, E.; Wang, Y. F.; Rodriguez, J. E.; Eiceman, G. A. Neural Network Recognition of Chemical Class Information in Mobility Spectra Obtained at High Temperatures. Anal. Chem. 2000, 72 (6), 1192–1198.

(6)

Bell, S.; Nazarov, E.; Wang, Y. F.; Eiceman, G. A. Classification of Ion Mobility Spectra by Functional Groups Using Neural Networks. Anal. Chim. Acta 1999, 394 (2–3), 121–133.

(7)

Eiceman, G. A.; Nazarov, E. G.; Rodriguez, J. E. Chemical Class Information in Ion Mobility Spectra at Low and Elevated Temperatures. Anal. Chim. Acta 2001, 433 (1), 53–70.

(8)

An, X.; Eiceman, G. A.; Rodriguez, J. E.; Stone, J. A. Gas Phase Fragmentation of Protonated Esters in Air at Ambient Pressure through Ion Heating by Electric Field in Differential Mobility Spectrometry. Int. J. Mass Spectrom. 2011, 303 (2–3), 181–190.

(9)

Ruszkiewicz, D. M.; Thomas, C. L. P.; Eiceman, G. A. Fragmentation, Auto-Modification and Post Ionisation Proton Bound Dimer Ion Formation: The Differential Mobility Spectrometry of Low Molecular Weight Alcohols. Analyst 2016, 141 (15), 4587–4598.

(10)

Field, F. H. Chemical Ionization Mass Spectrometry. XII. Alcohols. J. Am. Chem. Soc. 1970, 92 (9), 2672-2676.


Page 12 of 24

Page 13 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(11)

Munson, B.; Feng, T. -M; Ward, H. D.; Murray, R. K. Isobutane Chemical Ionization Mass Spectra of Unsaturated Alcohols. Org. Mass Spectrom. 1987, 22 (9), 606–609.

(12)

Karpas, Z.; Eiceman, G. A.; Ewing, R. G.; Harden, C. S. Collision Induced Dissociation Studies of Protonated Alcohol and Alcohol-Water Clusters by Atmospheric Pressure Ionization Tandem Mass Spectrometry. Part 2. Ethanol, Propanol and Butanol. Int. J. Mass Spectrom. Ion Process. 1994, 133 (1), 47–58.

(13)

Smith, S. C.; McEwan, M. J.; Giles, K.; Smith, D.; Adams, N. G. Unimolecular Decomposition of a Polyatomic Ion in a Variable-Temperature Selected-Ion-Flow-Drift Tube: Experiment and Theoretical Interpretation. Int. J. Mass Spectrom. Ion Process. 1990, 96 (1), 77–96.

(14)

Bell, A. J.; Giles, K.; Moody, S.; Watts, P. Studies on Gas-Phase Positive Ion—molecule Reactions of Relevance to Ion Mobility Spectrometry The Reactions of 2-Methyl-2-Propanol (t-Butyl Alcohol) with Protonated Water Clusters in an Ion Mobility System. Int. J. Mass Spectrom. Ion Process. 2003, 173 (1–2), 65–70.

(15)

Brown, P.; Watts, P.; Märk, T. D.; Mayhew, C. A. Proton Transfer Reaction Mass Spectrometry Investigations on the Effects of Reduced Electric Field and Reagent Ion Internal Energy on Product Ion Branching Ratios for a Series of Saturated Alcohols. Int. J. Mass Spectrom. 2010, 294 (2–3), 103–111.

(16)

Atkinson, J.R.; Clark, A.; Taylor S.J.; Munro, W.A., “Detection apparatus”, Patent Application 20090039248, Filed: April 20, 2006, Publication date: February 12, 2009.

(17)

Atkinson, J.R., “Combination ion gate and modifier”, Patent number: 9236233 Filed: January 20, 2012, Date of Patent: January 12, 2016.

(18)

Atkinson, J.R.; Clark, A.; Grant, B.; Taylor, S.J., “Ion Modification – A New Technology to Enhance the Selectivity of TOF-IMS Detectors,” Abstract Number: 150-8, March 8th, 2015, New Orleans, LA.

(19)

Chiluwal, U.; Lee, G.; Rajapakse, Y.; Willy, T.; Lukow, S.; Schmidt, H.; Eiceman, G.A., Tandem Ion Mobility Spectrometry at Ambient Pressure and Field Fragmentation of Mobility Selected Ions of Explosives and Interferents, Analyst 2019, 144, 2052-2061.

(20)

Eiceman, G. A.; Nazarov, E. G.; Rodriguez, J. E.; Stone, J. A. Analysis of a Drift Tube at Ambient Pressure: Models and Precise Measurements in Ion Mobility Spectrometry. Rev. Sci. Instrum. 2001, 72 (9), 3610–3621.

(21)

Kim, S. H.; Betty, K. R.; Karasek, F. W. Mobility Behavior and Composition of Hydrated Positive Reactant Ions in Plasma Chromatography with Nitrogen Carrier Gas. Anal. Chem. 1978, 50 (14), 2006–2012.

(22)

Kebarle, P.; Searles, S.K.; Zolla, A.; Scarborough, J.; Arshadi, M., The Solvation of the Hydrogen Ion by Water Molecules in the Gas Phase. Heats and Entropies of Solvation of Individual Reactions: H+(H20)n-1 + H20 - H+(H2O), J. Am.. Chem. Soc. 1967, 89, 6393-6399.

(23)

Wessel, M. D.; Sutter, J. M.; Jurs, P. C. Prediction of Reduced Ion Mobility Constants of Organic Compounds from Molecular Structure. Anal. Chem. 1996, 68 (23), 4237–4243.



(24)

Han, HY; Huang, GD; Jin, SP; Zheng, PC; Xu, GH; Li, JQ; Wang, HM; Chu, YN, Determination of alcohol compounds using corona discharge ion mobility spectrometry, J. Environ. Sci. 2007, 19, 751-755.

(25)

Jurado-Campos, N.; Garrido-Delgado, R.; Martínez-Haya, B.; Eiceman, G. A.; Arce, L. Stability of Proton-Bound Clusters of Alkyl Alcohols, Aldehydes and Ketones in Ion Mobility Spectrometry. Talanta 2018, 185, 299–308.

(26)

Bomse, D. S.; Beauchamp, J. L. Thermochemistry and Proton Bond Energies of Gas-Phase Proton-Bound Dimers of Aliphatic Alcohols. J. Phys. Chem. 1981, 85 (5), 488–492.

(27)

Ewing, R. G.; Eiceman, G. A.; Harden, C. S.; Stone, J. A. The Kinetics of the Decompositions of the Proton Bound Dimers of 1,4-Dimethylpyridine and Dimethyl Methylphosphonate from Atmospheric Pressure Ion Mobility Spectra. Int. J. Mass Spectrom. 2006, 255–256 (1–3), 76–85.

(28)

Eiceman, G. A.; Shoff, D. B.; Harden, C. S.; Snyder, A. P. Fragmentation of Butyl Acetate Isomers in the Drift Region of an Ion Mobility Spectrometer. Int. J. Mass Spectrom. Ion Process. 1988, 85 (3), 265–275.

(29)

Rajapakse, R. M. M. Y.; Stone, J. A.; Eiceman, G. A. An Ion Mobility and Theoretical Study of the Thermal Decomposition of the Adduct Formed between Ethylene Glycol Dinitrate and Chloride. Int. J. Mass Spectrom. 2014, 371 (3), 28–35.

(30)

Wanneer, G. H. On the Motion of Ions in a Strong Electric Field. I, Phys. Rev., 1951, 83 (c), 281– 289.

(31)

Wannier, G. H. Motion of Gaseous Ions in a Strong Electric Field. II, Phys. Rev., 1952, 87 (1), 795– 798.


Page 14 of 24

Page 15 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Values of Ko obtained at 89˚C for protonated monomers, proton bound dimers, and fragment ions from Mode 3 and Mode 4 with a reactive tandem ion mobility spectrometer. Compound

Ko MOH2+(H2O)n

Ko M2H+

propanol 1-butanol 1-pentanol 1-hexanol 1-heptanol 1-octanol 1-nonanol

1.91 1.79 1.65 1.54 1.47 1.41 1.34

1.69 1.47 1.35 1.23 1.15 1.09 1.02

2-butanol iso-butanol cyclohexanol

1.79 1.83 1.64

1.54 1.50 1.33

Ko Ko Fragment Fragment Mode 4 Mode 3 Primary alcohols 2.19 2.26 2.06 2.11 2.19 2.10 2.10 2.02 1.96 1.97 1.88 1.81 1.76 1.73 Other alcohols 2.15 2.21 2.15 2.21 2.10 2.07


ΔKo MOH2+(H2O)n - Fragment

Ko Ref23 MOH2+(H2O)n

0.28 0.31 0.54 0.50 0.49 0.47 0.42

1.93 1.80 1.71 1.62 1.54 1.47 1.40

0.36 0.37 0.47

1.85 1.84 -


Page 16 of 24

Table 2. Consecutive reaction enthalpies (kJ/mol) toward the final stable fragment ion of alcohols

Primary Alcohols Step

Other Alcohols

C3H7OH

C4H9OH

C5H11OH

C6H13OH

C7H15OH

C8H17OH

C9H19OH

2- C4H9OH

I

67.6

68.1

66.2

66.5

67.6

64.0

65.7

65.9

66.6

63.3

II

74.1

73.1

73.7

64.5

72.9

73.4

72.3

71.5

72.9

68.2

III

105.7

103.4

105.4

109.7

96.6

102.8

104.9

92.4

102.6

94.0

IV

97.1

85.9

81.6

76.5

78.1

76.6

76.8

69.5

43.9

61.8

Sum I to IV V

344.5

330.5

326.9

317.2

315.2

316.8

319.7

299.3

286

287.3

-52.1

-49.7

-51.6

-55.4

-49.1

-57.9

-56.8

-

-64.9

-

Net

292.4

280.8

275.3

261.8

266.1

258.9

262.9

299.3

221.1

287.3

*Key to Steps: I. Loss of water of hydration, n = 3 to n=2; ROH2+(H2O)3→ ROH2+(H2O)2+H2O II. Loss of water of hydration, n = 2 to n=1; ROH2+(H2O)2→ROH2+(H2O)+H2O III. Loss of water of hydration, n = 1 to n=0; ROH2+(H2O)→ROH2++H2O IV. Water loss to primary carbocation; ROH2+→M+’+H2O V. Charge/hydrogen migration to secondary carbocation M+’→M+’’ ‘primary carbocation ‘’secondary carbocation


i- C4H9OH

C6H11OH

Page 17 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


LIST OF FIGURES 1. Schematic of reactive tandem ion mobility spectrometer with dual ion shutters and wire grid pair (Grid 1 and 2) for electric field fragmentation of ions. Supporting electronics and utilities are not shown. 2. Ion mobility spectra without (dashed lines) and with (solid lines) electric field fragmentation at 120 Td and 67˚C. 3. Ion mobility spectra for mobility selected protonated monomers of alcohols at 67˚C without (dashed line) and with (solid line) electric field fragmentation at 120 Td. Carbon numbers 3 to 5. 4. Ion mobility spectra for mobility selected protonated monomers of alcohols at 67˚C without (dashed line) and with (solid line) electric field fragmentation at 120 Td. Carbon numbers 6 to 9. 5. Plots of drift time (Ko) for fragment ion against drift time (Ko) for protonated monomer for four chemical classes from reactive tandem ion mobility spectrometry. Chemical identities given in Supporting Information. 6. Fragmentation efficiency for mobility isolated protonated monomers from 68 to 121 Td at 67˚C.



Page 18 of 24

TABLE OF CONTENTS GRAPHIC

Product Ions from Source Region

Ion Mobility Separation

Mobility Isolation

Product Ions from Source Region

Electric Field Fragmentation


Page 19 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56


Figure 1. Shokri, et al Two Column Size (3.06″*7″)

First Drift Region (21.4 mm)

Ion Source and Reaction Region (41.8 mm) Front Flange

63 Ni

Second Drift Region (22.0 mm) Grid 1

Back Flange

Aperture Grid

Ion Source Combi ned Drift Length (43.4 mm)

Drift Gas Vent

Faraday Plate (Detector) Gri d 2 to Detector Length (19.5mm)

Inlet for Effluent from Gas Chromatograph

Ion Shutter 1

Ion Shutter 2


Grid 2

Drift Gas In

Figure 2. Shokri, et al Page 20 of 24 One Column size (3.3″*4.37″)


H+(H2O)n

A

0.8 MH+(H2O)n-x

C9H19+

0.4

Detector Response (V)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

0.0 0.8

M2H+

MH+(H2O)n-x

H+(H2O)n

B

C7H15+

0.4

M2H+

0.0 H+(H2O)n

1.6

C MH+(H2O)n-x

C5H11+

0.8 M2H+

0.0 5

6

7

8

9

Drift Time (ms)


10

Page 21 of 24

0.8

Figure 3. Shokri, et al One Column size (3.3″*4.52″)

MH+(H2O)n-x

C5H11+

1-pentanol

0.0 1.0


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56


MH+(H2O)n-x

1-butanol

MH+(H2O)n-x

isobutanol

C4H9+

0.0

0.8

C4H9+

0.0 0.8

2-butanol

MH+(H2O)n-x

C4H9+

0.0 1-propanol

MH+(H2O)n-x

0.8

0.0 1

C3H7+

2

3

4

Drift Time (ms)


5


MH+(H2O)n-x

C9H19+

1-nonanol

0.2

0.0

1-octanol C8H17+

MH+(H2O)n-x

0.2


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

Page 22 of 24 Figure 4. Shokri, et al One Column size (3.3″*4.33″)

0.0 0.4

1-heptanol MH+(H2O)n-x

C7H15+

0.0 1-hexanol

MH+(H2O)n-x

C6H13+

0.4

0.0 C5H11+

cyclohexanol

MH+(H2O)n-x

0.4

0.0 1

2

3

4

Drift Time (ms)


5

Page 23 of 24

Figure 5 One column Size 3.27″*4.17″

Ko of monomer gas ion (cm2 / V.s) 1.74

1.58

1.45

1.34

1.24

1.16

1.58

5.0

Ko of fragment gas ion (cm2 / V.s)

5.5

td of fragment gas ion (ms)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56


1.74

aldehydes

alcohols

1.93

4.5

acetates

4.0

2.17

alkanes

5.0

5.5

6.0

6.5

7.0

td of monomer gas ion (ms)


7.5


95 C6(cyc)

C5

Fragmentation Efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

24etofal24 Figure 6. Page Shokri, one column size (3.3″*4.18″)

C6

50 C7

C9 C8

C4 C4(iso) C3

C4(sec)

0 68

95

E/N(Td)


121

Reactive Tandem Ion Mobility Spectrometry with Electric Field

Recommend Documents