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

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CHAPTER 11_Xiao_Atomic Mass Spectrometry_2018



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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



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