DOCSLIB.ORG

Hydrogen Abstraction from Titanium and Zirconium Oxides

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Hydrogen Abstraction from Titanium and Zirconium Oxides The Pennsylvania State University The Graduate School Eberly College of Science NEW INSIGHTS IN THE GAS-PHASE ION CHEMISTRY OF GROUP IVB TRANSITION METAL OXIDES: CLUSTER MODELS FOR CATALYSIS A Dissertation in Chemistry by Christopher L. Harmon © 2016 Christopher L. Harmon Submitted in Partial Fulfillment Of the Requirements For the Degree of Doctor of Philosophy August 2016 The dissertation of Christopher L. Harmon was reviewed and approved* by the following: A. W. Castleman, Jr. Evan Pugh Professor of Chemistry and Physics Eberly Distinguished Chair in Science Dissertation Adviser Chair of Committee Nicholas Winograd Evan Pugh Professor of Chemistry Lasse Jensen Associate Professor of Chemistry Robert M. Rioux Friedrich G. Helfferich Associate Professor of Chemical Engineering Professor of Chemistry Kenneth S. Feldman Professor of Chemistry Graduate Program Chair *Signatures are on file in the Graduate School. ii Abstract The study of gas-phase cluster models has emerged as a useful tool to model catalytic active sites on surfaces. By observing how the reactivity of TMO clusters changes with cluster size, active site, and metal composition, we draw insights about the molecular factors governing reactivity and selectivity. The aim is to provide a conceptual framework to drive the development of improved catalysts with higher activity and selectivity. As group IVB transition metal oxides (TMOs) are widely used as catalysts and supports, we have undertaken mass spectrometric reactivity studies of titanium, zirconium, and hafnium oxide clusters with small organic molecules of interest in catalysis. We particularly note the differences in reactivity observed as the identity of the + metal in the cluster changes. We report the reactivity of MxO2x (M = Ti, Zr) clusters that contain radical atomic oxygen, O•−, with methane, ethane, propane, ethylene, and propylene. We observe that in many cases the titanium clusters undergo a type of “etching” reaction, where the cluster loses a TiO unit and associates the reactant gas. Zirconium oxides strongly prefer the hydrogen atom abstraction pathway, and no evidence for an etching type of reaction is found for zirconium clusters. Next, we examine + the reactivity of TixO2x+1 clusters that are theoretically predicted to contain a superoxide •− + active site, O2 , and find that the reactivity is quite different from ZrxO2x+1 . We also present one of the first studies of the reactivity of hafnium oxide clusters, and show that + + HfxO2x+1 acts very similarly to ZrxO2x+1 clusters, attributed to a superoxide active site. + However, Hf2O4 , which contains a radical oxygen atom, shows drastically different iii + reactivity from Zr2O4 . Finally, we discuss these studies in the context of isoelectronic superatoms. iv Contents List of Figures ..................................................................................................................... vii List of Tables ........................................................................................................................ x Acknowledgements ............................................................................................................. xi Introduction ....................................................................................................... 1 1.1 Catalysis .................................................................................................................. 1 1.2 Clusters: “Every Atom Counts” ............................................................................... 3 1.3 Clusters in Catalysis Research ................................................................................. 5 1.4 Outline of Dissertation .......................................................................................... 10 Experimental Apparatus .................................................................................. 11 2.1 Overview ............................................................................................................... 11 2.2 Vacuum System ..................................................................................................... 12 2.3 Ion Creation........................................................................................................... 13 2.4 TQMS System: Quadrupoles, Octopoles and Ion Optics ...................................... 15 2.5 Ion Detection ........................................................................................................ 18 2.6 Data Analysis ......................................................................................................... 19 Differing Selectivity and Reactivity of Stoichiometric Titanium and Zirconium Oxide Cations with Small Hydrocarbons: Observation of a TiO Etching Reaction ..... 22 3.1 Introduction .......................................................................................................... 22 3.2 Methods ................................................................................................................ 24 3.2.1 Experimental Methods ................................................................................ 24 3.2.2 Computational Methods .............................................................................. 26 3.3 Results and Discussion .......................................................................................... 27 3.3.1 Observation of a TiO Etching Reaction ........................................................ 27 3.3.2 Reactions with Methane .............................................................................. 30 3.3.3 Reactions with Ethane ................................................................................. 33 3.3.4 Reactions with Propane ............................................................................... 39 3.3.5 Reactions with Ethylene .............................................................................. 43 3.3.6 Reactions with Propylene ............................................................................ 46 3.3.7 Overall Relative Rates .................................................................................. 49 3.4 Conclusion ............................................................................................................. 52 + Further Reactions of Titanium Oxide Clusters: Superoxide Behavior of TixO2x+1 ? ..................................................................................................................................... 54 4.1 Introduction .......................................................................................................... 54 4.2 Methods ................................................................................................................ 55 4.2.1 Experimental Methods ................................................................................ 55 4.2.2 Computational Methods .............................................................................. 55 4.3 Results and Discussion .......................................................................................... 56 + 4.3.1 Calculated Structures of Ti2O2x+1 Clusters .................................................. 56 4.3.2 Revisiting Superoxide-Containing Zirconium Cluster Reactions: Correcting Assigned Reaction Products ............................................................................ 57 4.3.3 Titanium Superoxide Behavior ..................................................................... 60 v 4.4 Conclusion ............................................................................................................. 66 Preliminary Studies on Hafnium Oxide Reactivity ........................................... 67 5.1 Introduction .......................................................................................................... 67 5.2 Experimental Methods ......................................................................................... 69 5.3 Results and Discussion .......................................................................................... 69 + 5.3.1 HfxO2x+1 Reactions ....................................................................................... 69 + 5.3.2 Hf2O4 with Ethylene: Preference for the Oxidative Dehydrogenation Pathway........................................................................................................... 75 5.4 Conclusion ............................................................................................................. 78 Superatoms ...................................................................................................... 80 6.1 Development of the Concept of “Superatoms” .................................................... 80 6.2 Physical Explanations for the Phenomena ............................................................ 84 Conclusion and Future Directions .................................................................... 93 Appendix A. Theory of Quadrupole Operation ................................................................. 95 A-1. The Mathieu Equations of Motion ...................................................................... 95 A-2. Applications to Quadrupole Operation ............................................................. 102 Appendix B. Operating the Merlin Software .................................................................. 104 B-1. How Mass Scanning Works ................................................................................ 104 B-2. Data Collection Macros for the Merlin Software
Load more

Recommended publications
  • MASS SPECTROSCOPY APPLIED to GAS LEAK DETECTION and FUEL IONIZATION by JAYANTH POTHIREDDY a THESIS PRESENTED to the GRADUATE
    MASS SPECTROSCOPY APPLIED TO GAS LEAK DETECTION AND FUEL IONIZATION By JAYANTH POTHIREDDY A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2003 Copyright 2003 by Jayanth Pothireddy To my friends ACKNOWLEDGMENTS I would like to sincerely thank Dr. Corin Segal for giving me this wonderful opportunity and for his unlimited support, understanding and incredible patience without which I would not have successfully completed my thesis. I would also like to thank Dr. David Mikolaitis and Dr. Martin Vala for their support and Dr. Norman Fitz-Coy for his valuable suggestions. Many thanks go to Mr. Jan Szczepanski for giving me “first lessons” on mass spectrometry, invaluable suggestions, tremendous support and help in developing the mass spectrometry system. My heartfelt thanks go to my friends Venkat, Sujith, Gopi, Anand, “Iranian bros” Amir and Omid, Weizhong, Sampath, Harsha, Adil, Anant, Sasidhar, Charan, Danny, Jonas, Nelson, Zhu Wei, Ron, “Dr” Amit, Errol, Anurag, Priya, Amit “Saale” and Balaji for their support and understanding. I thank Ron Brown for constructing a nice model of the Space Shuttle aft compartment and for his help in moving the mass spectrometer cart to and fro from “chemistry” to “aero.” iv TABLE OF CONTENTS Page ACKNOWLEDGMENTS.................................................................................................. iv LIST OF FIGURES...........................................................................................................vii
    [Show full text]
  • Mass Spectrometry (Part-II) Electrostatic Acceleration System
    S.O.s. in environmental chemistry Jiwaji university, gwalior Presentation on:- Mass Spectrometry (part-II) Electrostatic Acceleration System:- 1) The positive ions formed in the ionisation chamber are withdrawn by the electric field which exists between the first accelerator plate and the second repeller plate. 2) A strong electrostatic field between accelerator and repeller plate accelerates the ions of masses m1 m2 m3... to their final velocities. 3) The ions which escape through slit having velocities and kinetic energies give. 2 2 2 eV=1/2m1v1 =1/2m2v2 =1/2m3v3 ...... Vacuum system:- 1) A high vacuum is to be maintained. 2) The inlet system is generally maintained at 0.015 torr, the ion source at 10-15 torr and analyzer tube at 10-7 torr or as low as possible. 3) Oil diffusion and mercury diffusion pumps are commonly used in different types of combination Mass analyzers:- 1) Separate ions based on their mass-to-charge ratio (m/z) 2) Operate under high vacuum (keeps ions from bumping into gas molecules) 3) Actually measure mass-to-charge ratio of ions (m/z) Types of mass analyzers:- 1) Quadrupole mass analyzer 2) Time of flight analyzer (TOF) 3) Magnetic sector mass analyzer a) Single focusing b) Double focusing 4) Quadrupole ion trap mass analyzer Quadrupole mass analyzer:- 1) It consists of 4 voltage carrying rods. 2) The ions are pass from one end to another end 3) During this apply the radiofrequency and voltage complex oscillations will takes place. 4) Here the single positive charge ions shows the stable oscillation and the remaining the shows the unstable oscillations Magnetic Sector Mass Analyzer:- In magnetic sector analyzers ions are accelerated through a flight tube, where the ions are separated by charge to mass ratios.
    [Show full text]
  • Quadrupole and Ion Trap Mass Analysers and an Introduction to Resolution a Simple Definition of a Mass Spectrometer
    Quadrupole and Ion Trap Mass Analysers and an introduction to Resolution A simple definition of a Mass Spectrometer ◗ A Mass Spectrometer is an analytical instrument that can separate charged molecules according to their mass–to–charge ratio. The mass spectrometer can answer the questions “what is in the sample” (qualitative structural information) and “how much is present” (quantitative determination) for a very wide range of samples at high sensitivity Components of a Mass Spectrometer Atmosphere Vacuum System Sample Ionisation Mass Data Detector Inlet Method Analyser System How are mass spectra produced ? ◗ Ions are produced in the source and are transferred into the mass analyser ◗ They are separated according to their mass/charge ratio in the mass analyser (e.g. Quadrupole, Ion Trap) ◗ Ions of the various m/z values exit the analyser and are ‘counted’ by the detector What is a Mass Spectrum ? ◗ A mass spectrum is the relative abundance of ions of different m/z produced in an ion source -a “chemical fingerprint” ◗ It contains – Molecular weight information (generally) – Structural Information (mostly) – Quantitative information What does a mass spectrum look like ? ◗ Electrospray mass spectrum of salbutamol + 100 MH 240 OH NH tBu HO Base peak HO % at m/z 240 241 0 60 80 100 120 140 160 180 200 220 240 260 280 300 What information do you need from the analysis ? ◗ Low or High Mass range ◗ Average or Monoisotopic mass (empirical) ◗ Accurate Mass ◗ Quantitation - precision, accuracy, selectivity ◗ Identification ◗ Structural Information
    [Show full text]
  • Mechanistic Study of Carbazole and Triphenylamine Dimerization and Pyrrolidine
    Mechanistic Study of Carbazole and Triphenylamine Dimerization and Pyrrolidine Dehydrogenation Using Mass Spectrometry A thesis presented to the faculty of the College of Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Master of Science Brian E. Hivick May 2019 © 2019 Brian E. Hivick. All Rights Reserved. 2 This thesis titled Mechanistic Study of Carbazole and Triphenylamine Dimerization and Pyrrolidine Dehydrogenation Using Mass Spectrometry by BRIAN E. HIVICK has been approved for the Department of Chemistry and Biochemistry and the College of Arts and Sciences by Hao Chen Professor of Chemistry and Biochemistry Joseph Shields Interim Dean, College of Arts and Sciences 3 ABSTRACT HIVICK, BRIAN E., M.S., May 2019, Chemistry Mechanistic Study of Carbazole and Triphenylamine Dimerization and Pyrrolidine Dehydrogenation Using Mass Spectrometry Director of Thesis: Hao Chen Mass spectrometry is one of the most powerful techniques used in analytical chemistry today. It has been utilized in a wide variety of fields, from synthesis to pharmaceuticals to analyzing medicinal samples. One of its greatest strengths is its ability to be combined with other techniques to further improve the collected data. In this work, the ability to couple mass spectrometry with electrochemistry in the dimerization of two aromatic amines, carbazole and triphenylamine, is explored, and insight into the underlying dimerization mechanism is achieved. In addition, photochemistry is also coupled with mass spectrometry, and the potential dehydrogenation of pyrrolidine is explored. 4 DEDICATION I dedicate this work to my parents and siblings, who have done so much for me throughout my life and have unequivocally supported me in all of my decisions.
    [Show full text]
  • Agilent 6545 Q-TOF Mass Spectrometer
    The Agilent 6545 Q-TOF mass spectrometer The Agilent 6545 Q-TOF mass spectrometer, which is shown in the following picture, is a state-of-the-art quadrupole time-of-flight (Q-TOF) mass spectrometer that performs both high resolution mass spectrometry (HRMS) and high-resolution tandem mass spectrometry (HRMS/MS). It consists of a quadrupole mass analyzer, a hexapole collision cell, and a high resolution TOF mass analyzer. During HRMS analysis, the quadrupole mass analyzer and the hexapole collision cell are simply used as ion guides to transport ions. During HRMS/MS analysis, the quadrupole mass analyzer selects precursor ions that are fragmented in the hexapole collision cell into product ions, which are then impelled to the TOF mass analyzer, at an angle perpendicular to the original path. 1 The following Figure shows the ion optics of the Agilent 6545 Q-TOF mass spectrometer, with major improvements over the Agilent 6540 Q-TOF mass spectrometer identified. 1. Enhanced Wide Bore Lens 2. Identical to the lens 2 design used in the 6560, a larger orifice is used in the 6545. Ions are still conditioned via DC and RF voltages prior to quad transmission or isolation, but ions will not get in close proximity to the lens surface. The possible risk of ion deposition on the surface is greatly reduced, leading to an increased robustness of the system under high ion current conditions. 2. Slicer design. The slicer design on the 6545 is identical to the 6550. It has 2 different sizes of the opening: a larger one for high sensitivity applications, and a smaller one for high resolution applications.
    [Show full text]
  • Mass Spectrophotometry: an Advanced Technique in Biomedical
    s in que Bio ni lo h g c y e T & d M e e Paital, Adv Tech Biol Med 2016, 4:3 c Advanced Techniques in d n i c a i v n DOI: 10.4172/2379-1764.1000182 d e A ISSN: 2379-1764 Biology & Medicine Review Article OpenOpen Access Access Mass Spectrophotometry: An Advanced Technique in Biomedical Sciences Biswaranjan Paital* Department of Zoology, CBSH, Orissa University of Agriculture and Technology, Bhubaneswar, 751003, Odisha, India Abstract Present century is the era of life sciences and metabolomics is the dominating field in present day over genomics and proteomics. Powerful techniques in the later cases are useful to determine the qualitative and quantitative studies of the levels of metabolites in bio-medical samples. In past time, biochemistry had very least role because the analyses of metabolites using individual conventional biochemical techniques had been used from past centuries. Owing to this limitation, mass spectrometry (MS) was introduced in bio-medical sciences. The fundamental rule in MS is that it ionizes individual chemical species and sorts the fragmented samples at charged state (ions) on the basis of their mass to charge (m/z) ratio. Therefore, each molecule in purified form or in homogenate can be identified and quantified based on their unique m/z ratio. In other words, MS measures the masses of the fragmented samples by enabling them to be charged during measurement. This particular technique has therefore, many applications starting from quantitative to qualitative analyses of metabolites under normal, experimental and diseased conditions in organisms including human being.
    [Show full text]
  • Mass Spectrometry Interfaced with Ion Mobility Or
    MASS SPECTROMETRY INTERFACED WITH ION MOBILITY OR LIQUID CHROMATOGRAPHY SEPARATION FOR THE ANALYSIS OF COMPLEX MIXTURES A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Danijela Smiljanic December, 2011 MASS SPECTROMETRY INTERFACED WITH ION MOBILITY OR LIQUID CHROMATOGRAPHY SEPARATION FOR THE ANALYSIS OF COMPLEX MIXTURES Dissertation Danijela Smiljanic Approved: Accepted: ________________________________ _________________________________ Advisor Department Chair Dr. Chrys Wesdemiotis Dr. Kim C. Calvo ________________________________ _________________________________ Committee Member Dean of the College Dr. Bi-min Zhang Newby Dr. Chand K. Midha ________________________________ _________________________________ Committee Member Dean of the Graduate School Dr. David Perry Dr. George R. Newkome ________________________________ _________________________________ Committee Member Date Dr. Yi Pang ________________________________ Committee Member Dr. Peter Rinaldi ii ABSTRACT This dissertation focuses on coupling separation techniques such as ion mobility (IM) and liquid chromatography (LC) to mass spectrometry and their application to characterization of complex mixtures. Non-covalent complexes between poly(ethylene imine) (PEI) and single stranded oligodeoxynucleotides (ODNs), as well as components from black raspberries, were characterized utilizing ion mobility mass spectrometry (IM- MS) and liquid chromatography mass spectrometry (LC-MS),
    [Show full text]
  • M T T F Mass Spectrometry of Proteins, Peptides and Other Proteins
    MttfMass spectrometry of proteins, peptides and other analytes: principles and priilincipal meth hdods MttRMatt Ren frow January 7, 2011 Objectives of the Lecture 1. MkMake ions 2. Separate/Analyze 3. Detect ions 4. What is mass resolution and mass accuracy? What does a mass spectrometer do? 1. It measures mass better than any other technique. 2. It can give information about chemical structures. What are mass measurements good for? To identify, verify, and quantitate: metabolites, recombinant proteins, proteins isolated from natural sources, oligonucleotides, drug candidates, peptides, synthetic organic chemicals, polymers How is mass defined? Assigning numerical value to the intrinsic property of “mass” is based on using carbon-12, 12CasaC, as a reference point. One unit of mass is defined as a Dalton (Da). One Da lton is de fine d as 1/12 t he mass o f a s ing le carbon-12 atom. Thus, one 12C atom has a mass of 12.0000 Da. Isotopes +Most elements have more than one stable isotope. For example, most carbon atoms have a mass of 12 Da, but in nature, 1.1% of C atoms have an extra neutron, making their mass 13 Da. +Why do we care? Mass spec trome ters can “ see” i so tope peak s if th ei r resol uti on is high enough. If an MS instrument has resolution higggh enough to resolve these isotopes, better mass accuracy is achieved. Stable isotopes of most abundant elements of peptides Element Mass Abundance H 1.0078 99.985% 2.0141 0.015 C 12.0000 98.89 13.0034 1.11 N 14.0031 99.64 15.
    [Show full text]
  • 7. Atomic-Level Analysis and Catalytic Activity of Size-Selected Pt Clusters Deposited on Tio 2
    R&D Review of Toyota CRDL, Vol.42 No.1 (2011) 51-62 51 Special Feature: Automotive Exhaust Catalyst Research Report Atomic-level Analysis and Catalytic Activity of Size-selected Pt Clusters Deposited on TiO2(110) Yoshihide Watanabe, Noritake Isomura, Hirohito Hirata and Xingyang Wu Report received on Jan. 20, 2011 A new experimental setup to study catalytic and electronic properties of size-selected clusters on metal oxide substrates for developing heterogeneous catalysts, such as automotive exhaust catalysts, has been developed. The apparatus consists of a size-selected cluster source, a photoemission spectrometer, a scanning tunneling microscope (STM), and a high-pressure reaction cell. The high-pressure reaction cell measurements provide information on catalytic properties under conditions close to those in n practical uses. We investigated size-selected Ptn ( = 4, 7-10, 15) clusters deposited on TiO2(110) under soft- landing conditions. The catalytic activity measurements showed that the catalytic activities have a cluster size dependence. We obtained atomic-resolution images of size-selected clusters on surfaces, enabling the identification of atomic alignment in the clusters. Clusters smaller than Pt7 lay flat on the surface with a n planar structure, and a planar-to-three-dimensional (3D) transition occurred at = 8 for Ptn clusters on TiO2. f n The binding energies of Pt 4 7/2 decreased steeply with increasing cluster size up to = 7 for Ptn, and decreased gradually for n ≥ 8. This inflection point (n = 8) agrees well with the cluster size at the planar-to- 3D transition. It was found that the core-level shifts of size-selected Pt clusters on TiO2 are closely correlated with cluster geometries.
    [Show full text]
  • Collision-Induced Dissociation of 4-Imidazolone Ions, Isomers of [Bn
    Collision-induced dissociation of 4-imidazolone ions, isomers + of [bn] derived from peptides after water loss Ka Hang Brian Lam A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE GRADUATE PROGRAM IN CHEMISTRY YORK UNIVERSITY TORONTO, ONTARIO April 2018 © Ka Hang Brian Lam, 2018 Abstract + Collision-induced dissociation spectra of protonated peptides [(aminoacid)n + H] form, after the loss of + water, nominal [bn] ions which are dependent on both peptide length and amino acid sequence. Protonated tetraglycine loses water predominantly from the first amide; loss from the second amide is a + minor channel. The resultant [b4] ions have identical CID spectra, indicating interconversion prior to dissociation. Protonated pentaglycine loses water from the first and second amides in high abundances, + and the resulting CID spectra of the [b5] ions are different, suggesting that interconversion is no longer + the dominant pathway. The [b6] ions of hexaglycine, formed from the first three amides are in high abundance and their CID spectra are not identical. The substitution of an alanine or proline for a glycine + of tetraglycine generally showed reduced water loss and the [b4] ions had different fragmentation + pathways than those of the [b4] ions of tetraglycine. ii Acknowledgements I would like to thank my supervisors Alan C. Hopkinson and K.W. Michael Siu for their support, for which I am eternally grateful. Professor Hopkinson has been instrumental in teaching me about gas phase fragmentation by collision-induced dissociation. I have learned a lot about mass spectrometry as well as life.
    [Show full text]
  • Mass Spectrometry-Based Analysis to Investigate the Pharmacokinetics and Proteomic Properties of a Viral Sensitizer
    Mass Spectrometry-based Analysis to Investigate the Pharmacokinetics and Proteomic Properties of a Viral Sensitizer by Emma Anne Wistaff A thesis submitted to the Faculty of Graduate and Postdoctoral Affairs in partial fulfillment of the requirements for the degree of Master of Science in Chemistry Carleton University Ottawa, Ontario © 2021, Emma Anne Wistaff Abstract Attenuated oncolytic viruses (OVs) are a promising alternative cancer therapy to mainstream methods such as radiotherapy and chemotherapy. OV therapy takes advantage of the defective antiviral response present in most cancer cells however heterogeneity amongst target cells and attenuation of OVs to increase their safety profiles has limited the efficacy of this treatment. Our collaborative research group has developed novel small molecules named viral sensitizers (VSes) capable of enhancing viral infection and cancer- specific cell death. In this study, liquid chromatography-mass spectrometry (LC-MS) methods were developed to study the pharmacokinetic (PK) metabolic activity of VSe1-28 through in vitro time course experiments. Furthermore, glutathione (GSH) was identified as an active target for VSe1-28 and two GSH metabolites were identified in vitro. It was found that VSe1-28 has a half-life of 3.90 hrs in lysate and 4.83 hrs in growth media. Parallel to this work, proteomic experiments were conducted to confirm the molecular target and mechanism of action of VSe1-28. VSe1-28 has been suspected to inhibit the nuclear translocation of NF-kB p65 in viral resistant cancer cells through in vitro and in vivo VSe1-28 modified protein experiments. An MRM method was developed to monitor the formation of the suspected molecular target of interest and a modified tryptic digestion protocol was developed specifically for our work.
    [Show full text]
  • Mass Spectroscopy Reference Books: 1) Analytical Chemistry by Gary D
    Mass Spectroscopy Reference Books: 1) Analytical Chemistry by Gary D. Christian 2) Principles of instrumental Analysis by Skoog, Holler, Crouch 3) Fundamentals of Analytical Chemistry by Skoog 4) Basic Concepts of analytical Chemistry by S. M. Khopkar Mass Analyzers Several devices are available for separating ions with different mass-to-charge ratios. Ideally, the mass analyzer should be capable of distinguishing minute mass differences. In addition, the analyzer should allow passage of a sufficient number of ions to yield readily measurable ion currents. These two properties are not entirely compatible, and design compromises must be made. Resolution of Mass Spectrometers The capability of a mass spectrometer to differentiate between masses is usually stated in terms of its resolution R, which is defined as 푚 푅 = ∆푚 where ∆푚 is the mass difference between two adjacent peaks of equal intensity that are just resolved and m is the nominal mass of the first peak (the mean mass of the two peaks is sometimes used instead). Two peaks are considered to be separated if the height of the valley between them is no more than a given fraction of their height (often 10%). Thus, a spectrometer with a resolution of 4000 would resolve peaks at m/z values of 400.0 and Magnetic Sector Analyzers Magnetic sector analyzers use a permanent magnet or an electromagnet to cause the beam from the ion source to travel in a circular path, most commonly 180°, 90°, or 60°. Figure shows a 90° sector instrument in which ions formed by EI are accelerated through slit B into the metal analyzer tube, which is maintained at an internal pressure of about 10-5 Pa.
    [Show full text]