FIU CHM 4130 - CHAPTER 11_Xiao_Atomic Mass Spectrometry_2018 (123 pages)

Previewing pages 1, 2, 3, 4, 5, 6, 7, 8, 57, 58, 59, 60, 61, 62, 63, 64, 65, 116, 117, 118, 119, 120, 121, 122, 123 of 123 page document View the full content.
View Full Document

CHAPTER 11_Xiao_Atomic Mass Spectrometry_2018



Previewing pages 1, 2, 3, 4, 5, 6, 7, 8, 57, 58, 59, 60, 61, 62, 63, 64, 65, 116, 117, 118, 119, 120, 121, 122, 123 of actual document.

View the full content.
View Full Document
Unformatted text preview:

Atomic Mass Spectrometry Nearly all elements in the periodic table can be determined by mass spectrometry More selective and sensitive than optical instruments Simple spectra Isotope ratios Much more expensive instrumentation An Overview of Elemental Analysis via Atomic Spectroscopy Atomic spectrometry systems 1 5 Figure 1 3 Atomic spectrometry systems containing free atoms and ions of the element of interest Figure 1 3 shows the instrumental arrangements for four different techniques used to detect these atoms or ions sorts the radiation by wavelength The radiation is detected and turned into electronic signals that are converted into concentration information for the analyst A representation of the layout of a typical ICP OES instrument is shown in Figure 3 1 ICP OES Instrument ICP Quadrupole Mass Analyzer The four main components of a Atomic mass spectrometer All ions Selected ions Detector Inlet Ionization Source Ion Accelerator Mass Analyzer Lets talk about mass Atomic mass of Carbon Atomic mass of Chlorine Atomic mass of Hydrogen Lets talk about mass Atomic mass of Carbon 12 000000000000000000000000000 amu Atomic mass of Chlorine 35 4527 amu Atomic mass of Hydrogen 1 00794 amu 1amu atomic mass units 1 dalton Da What about isotopes Atomic mass of Carbon 12 000 amu for 12C but 13 3355 for 13C Atomic mass of Chlorine 34 9688 amu for 35Cl and 36 9659 for 37Cl Atomic mass of Hydrogen 1 00794 amu for H and 2 0141 for D Just for clarification Atomic mass amu atomic mass units Da or Dalton kD kiloDalton for macromolecules 1 amu 1 Da 1 66056 10 27 kg proton mp 1 67265 10 27 kg neutron mn 1 67495 10 27 kg Ways to define and calculate the mass of an atom molecule or ion Average mass calculated using the atomic weight which is the weighted average of the atomic masses of the different isotopes of each element in the molecule find it in periodic table Nominal mass calculated using the mass of the predominant isotopes of each element rounded to the nearest integer value that corresponds to the mass number Monoisotopic mass calculated using the extract mass of the most abundance isotope for each constituent element Use monoisotopic mass if possible in MS Average mass Mass Weights of Atoms and Molecules element C H nominal exact Percent average mass mass abundance mass 12 12 00000 98 9 13 13 00335 1 1 1 1 007825 99 98 2 2 0140 0 02 12 00115 1 00794 Mass or Molecular Weight of molecules C20H42 Average Nominal Monoisotopic 20 x 12 011 42 x 1 00794 282 5535 20 x 12 42 x1 282 u 20 x12 42 x 1 007825 282 33 C100H202 Average Nominal Monoisotopic 100x12 011 202x1 00794 1404 7039 100x12 202x1 1402u 100x12 202x1 007825 1403 5807 Exact Masses of Some Common Elements and Their Isotopes Element Symbol Exact Mass u Rel Abundance Hydrogen 1H 1 007825037 100 0 Deuterium 2H or D 2 014101787 0 015 Carbon 12 12C 12 00000 100 0 Carbon 13 13C 13 003354 1 11223 Nitrogen 14 14N 14 003074 100 0 Nitrogen 15 15N 15 00011 0 36734 Oxygen 16 16O 15 99491464 100 0 Oxygen 17 17O 16 9991306 0 03809 Oxygen 18 18O 17 99915939 0 20048 Fluorine 19F 18 998405 100 0 Sodium 23Na 22 9897697 100 0 Silicon 28 28Si 27 9769284 92 23 Silicon 29 29Si 28 9764964 5 0634 Silicon 30 30Si 29 9737717 3 3612 Phosphorus 31P 30 9737634 100 0 Sulfur 32 32S 31 972074 100 0 Sulfur 33 33S 32 9707 0 78931 Sulfur 34 34S 33 96938 4 43065 Sulfur 36 36S 35 96676 0 02105 Chlorine 35 35Cl 34 968854 100 0 Chlorine 37 37Cl 36 965896 31 97836 Mass to Charge Ra o Unitless ratio of its mass number to the number of fundamental charge m z For 12C1H4 m z 16 0313 1 16 0313 For 13C1H42 m z 17 0346 2 8 5173 The mass to charge ratio is termed as mass due to singly charged ion Types of Atomic Mass Spectrometry Basic components of a mass spectrometry system Ionization Source Inlet Mass Analzyer all ions Detector selected ions Data System Laser ablation LA ICP MS Ablation cell Ablation cell Ablation cell 1 Ionization Source 8 000 to 10 000 oC Plasma Torches ICP MS interface Accelerated positive Ion beam The interface region of an ICP MS Sampler Skimmer Photo by A L Gray Dr Houk Presentation 2002 Two cone design vs three cone design After the ion beam exists the interface Ion deflection device separating ions from neutrals and photons After the ion beam exists the interface The collision reaction cell removing minor large interferences from the analyte ions standard mode for elements where interferences are not present in collision mode for removal of minor interference in reaction mode for removal of large interferences Basic components of a mass spectrometry system Ionization Source Inlet Mass Analzyer all ions Detector selected ions Data System Different types of Mass Analyzers which differ in the physical properties they manipulate Electric Quadrupole which depends on AC DC Currents Magnetic which depends on Voltage Time of Flight which depends on Mass Common to these Mass Analyzers is the separation of particles on the basis of mass to charge ratios m q Separation of Masses in a Mass Spectrometer 2 Mass Analyzer Quadrupole Schematic of quadrupole mass filter Quadrupole Analyzer y z x Ion trajectories in a Quadrupole with ac without dc voltage x z y http www youtube com watch v pjCun7QF19U http www youtube com watch v L k AnlLn2s How does it work U Vcoswt m z 900 m z 1000 m z 990 M1 M2 M3 U Vcoswt m z 1010 m z 1100 Quadrupole Benefits Classical mass spectra Good reproducibility Relatively small and low cost systems Limitations Limited resolution Peak heights variable as a function of mass mass discrimination Peak height vs mass response must be tuned Not well suited for pulsed ionization methods Applications Majority of benchtop GC MS and LC MS systems Triple quadrupole MS MS systems Sector quadrupole hybrid MS MS systems Time of Flight Mass Analyzers Time of Flight Mass Analyzers Extraction grid Steering grid repeller plate accelerating grid skimmer B A D C E F Mass Separation Potential energy relationship in a reflector TOF MS Reflector TOF MS E is the extraction pulse potential s is the length of flight tube over which E is applied d is the length of field free drift zone t is the measured time of flight of the ion Linear potential Reflectrons ion mirrors have two properties that enhance the resolving power of an instrument 1 The length of the flight path is increased greater flight time and greater time between the arrival of similar m z increase t 2 The arrival time distribution at the detector is reduced a reduction in the arrival time distribution decrease


View Full Document

Access the best Study Guides, Lecture Notes and Practice Exams

Loading Unlocking...
Login

Join to view CHAPTER 11_Xiao_Atomic Mass Spectrometry_2018 and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view CHAPTER 11_Xiao_Atomic Mass Spectrometry_2018 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?