The Mass Spectrograph

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The Mass Spectrograph Average Atomic Mass
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Inventor

• Francis William Aston won the 1922 Nobel Prize in
  Chemistry for his work in mass spectrometry

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The First Mass Spectrograph
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How Does it Work?
Schematics of a simple mass spectrometer with
sector type mass analyzer. This one is for the
measurement of Carbon dioxide isotope ratios
(IRMS) as in the carbon-13 urea breath test
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The Detector

• A continuous dynode particle multiplier detector.

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The Data
Mass Spectrograph of a protein
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The Data as a Bar Graph
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The Modern Mass Spectrograph
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• Use of Inductively Coupled Plasma-Mass
• Spectrometry in Boron-lO Stable Isotope
• Experiments with Plants, Rats, and Humans
• Richard A. Vanderpool1, Deb Hoff1, and Phyllis E.
  Johnson2
• 'United States Department of Agriculture,
  Agricultural Research Service, Grand Forks, North
  Dakota 2United
• States Department of Agriculture, Agricultural
  Research Service, Albany, California
• The commercial availability of inductively
  coupled plasma-mass spectrometry technology
  (ICP-MS) has presented the opportunity to measure
  the
• boron concentrations and isotope ratios in a
  large number of samples with minimal sample
  preparation. A typical analytical sequence for
  fecal samples
• consists of 25 acid blanks, 1 digestion blank, 5
  calibration solutions, 4 standard reference
  material solutions, 10 samples, and 4 natural
  abundance
• bias standards. Boron detection limits (3 x 1a)
  for acid blanks are 0.11 ppb for '0B, and 0.40
  ppb for " B. Isotope ratios were measured in
  fecal
• samples with 20 to 50 ppb boron with lt2 relative
  standard deviation. Rapid washout and minimal
  memory effects were observed for a 50 ppb
• beryllium internal standard, but a 200 ppb boron
  biological sample had a 1.0 ppb boron memory
  after a 6-min washout. Boron isotope ratios in
  geological
• materials are highly variable apparently this
  variability is reflected in plants. The lack of a
  fixed natural abundance value for boron requires
  that
• a natural abundance ratio be determined for each
  sample or related data set. The natural abundance
  variability also prevents quantitation and
  calculation
• of isotope dilution by instrument-supplied
  software. To measure boron transport in animal
  systems, 20 pg of 'B were fed to a fasted rat.
  During
• the 3 days after a 10B oral dose, 95 of the '0B
  was recovered from the urine and 4 from the
  feces Urinary isotope ratios, I B/0B, changed
  from
• a natural abundance of 4.1140 to an enriched
  value of 0.9507, a 77 change. The 'B label in
  perfused rat livers peaked within 3 hr (gt90
  recovery,
• 56 change in " B/B) and returned to a natural
  abundance ratio within 24 hr. In summary, boron
  concentrations and enriched isotope ratios have

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Note

• Percent out of 100
• Relative abundance out of one whole
• Average Atomic Mass the average mass of all the
  naturally occuring isotopes of an element
  expressed in atomic mass units.

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The Mass Spectrograph for the common isotopes of
Boron
The relative sizes of the peaks gives you a
direct measure of the relative abundances of the
isotopes. The tallest peak is often given an
arbitrary height of 100 - but you may find all
sorts of other scales used. It doesn't matter in
the least. You can find the relative abundances
by measuring the lines on the stick diagram. In
this case, the two isotopes (with their relative
abundances) are boron-10 18.70, 10.013
g/mol boron-11 81.30, 11.009 g/mol

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Sample Problems

• What is average atomic mass of Lithium if 7.42
  exists as 6Li (6.015 g/mol) and 92.58 exists as
  7Li (7.016 g/mol)?
• Two isotopes of silver are found using the mass
  spectrograph. Silver 107 has an atomic mass of
  106.91 amu and an abundance of 51.86 . The
  second isotope has an abundance of 48.14 , but
  its atomic mass was unable to be determined.
  What is the atomic mass and the mass
  number(identity) of this isotope?