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15.1.3 Uses of Mass
spectrometry -
Uses & applications of mass
spectroscopy in analysis, investigating molecular structure & identification of compounds
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Dr Phil Brown PhD:
Doc Brown's advanced level organic chemistry exam revision notes
on mass spectrometry suitable for students of UK based A level and IB chemistry courses & US K12 grade
11, grade 12 and AP honors chemistry courses
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All my advanced A level organic chemistry notes
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15.1.0
An introduction to
mass spectrometry and its applications
(written before
the extra sections and links below, so, some overlap!)
15.1.1
Index of mass spectra of
organic compounds
15.1.2
Mass spectrometry
applied to organic molecules - interpreting spectra -
fragmentation patterns
15.1.3
More on the uses and applications of mass spectrometry,
mainly in organic chemistry
(THIS PAGE)
15.1.4
Database of accurate m/z values and
possible identity of ions formed in mass spectrometry
15.1.3 Sub-index for this page
- more on the uses and applications of mass spectrometry
(a)
Application of
isotopic analysis
(b)
Advantages of using mass
spectrometry as an analytical technique
(c)
Indentifying a
molecule from the molecular ion peak and fragmentation pattern
(d)
Analysis and
identification using gas chromatography linked with mass spectrometry
(a)
Applications of isotopic analysis
(these sections open up in a new window for convenience)
(i) Analysing the ratio of isotopes of an element
You can measure
very accurate masses of specific isotopes to at least 9 significant figures with high resolution
mass spectrometers.
You can measure the relative abundances of
the isotopes for a specific element - from this you can calculate the
relative atomic mass of an element to at least 9 significant figures
(which can also be measured from chemical analysis).
Simple examples are
described and explained via the three links below.
The mass spectrum of chlorine -
isotope peak ratios - calculating relative atomic mass
The mass spectrum of strontium -
isotope peak ratios - calculating relative atomic mass
Analysing the mass spectrum of bromine
- isotope peak ratios
(ii) Radiocarbon dating in archaeology
Archaeological dating
of material using the isotope
carbon-14 residue
(iii) Dating rocks
Geological dating of igneous rocks
by measuring isotope ratios
TOP OF PAGE
and sub-indexes
(b) Advantages of using mass
spectrometry as an analytical technique
Like other modern instrumental analytical techniques used in
chemistry in the 20th-21st centuries, mass spectrometry has several
advantages over traditional methods of chemical analysis e.g.
It is a very sensitive
technique, only requiring tiny amounts of material for analysis
and only tiny amounts might be available e.g. in forensic
analysis of a crime scheme, drug analysis.
It is a very accurate
technique, but the mass spectrometer does require careful
calibration e.g. relative to carbon-12 isotope given an
arbitrary value of
12.0000 atomic mass units and quality instruments rarely make a
mistake.
The analysis can be done
quickly AND continuously.
A sampling system connected to a mass spectrometer
system can monitor pollution or a chemical production process
24/7!
A mass spectrometer can be
linked to other analytical instruments e.g. you can set up a
mass spectrometer to sample the separate molecules exiting from
a gas chromatograph column. see
section (d)
As a result of improved technology, the
applications of mass spectrometry include forensic toxicology,
drug development and identification of active ingredients, drug
testing and discovery, food contamination detection, pesticide
residue analysis in water or soil samples and protein
identification.
It is possible to detect extremely low levels
of organic compounds in the most complex of mixtures,
including sports anti-doping analysis and chemical warfare agent
detection
TOP OF PAGE
and sub-indexes
(c) Indentifying a molecule from the molecular ion peak and
fragmentation pattern
You
can
identify a molecular formula using a high resolution mass
spectrometer from a very accurate molecular mass.
However, if isomers
are possible, you need more data to ascertain its molecular
structure.
It
is possible to investigate aspects of a molecular structure from the
mass spectrum fragmentation pattern.
If the molecule is
known and the mass spectrum obtained for a pure sample,
identification of an organic molecule is possible from
its unique fragmentation patterns
(a mass spectra fingerprint) - but the database data must be
obtained under the same experimental conditions i.e. the same instrument
settings on the mass spectrometer.
For examples of
identifying molecular formula from the molecular ion peak see
Isotopic masses and accurate molecular ion peaks
to identify molecules and molecular formulae
show a comparison of spectra e.g. isomers
TOP OF PAGE
and sub-indexes
(d)
Analysis
and identification using gas chromatography linked with mass
spectrometry (GC-MS)
The diagram below shows how a gas
chromatograph can be linked to a mass spectrometer.
The chromatographic column coating
(stationary immobile phase surface) separates the components
in the mixture as they are carried along by the carrier
gas (mobile phase).
The detector (many types) measures
the amount of each component as they come through the
column and simultaneously a sample can be tapped off to
the mass spectrometer.
(I've shown the sampling for the mass
spectrum immediately after the detector, but if it was a
flame ionization detector, you would have to sample
immediately before the detector).
Each component molecule can be identified
from the very accurate molecular ion peak m/z and the
fragmentation pattern, assuming the molecule is known in the
database.
Even if it cannot be identified, the
molecular formula can be obtained from a very accurate m/z
value for the parent molecular [M]+ ion.
High temperature gas chromatography can be
used to analyse for large molecules including fats and oils,
so finds a use in developing biofuels.
Fragrances - perfumes can be developed by
analysing natural oils from plants.
In astrochemistry GC-MS systems were
taken to Mars by the Viking program. Venera 11 and 12 and
Pioneer Venus analysed the atmosphere of Venus with GC-MS.
The Huygens probe of the Cassini–Huygens mission landed one
GC-MS on Saturn's largest moon, Titan.
The MSL Curiosity rover's sample analysis at
Mars (SAM) instrument contains both a gas chromatograph and
quadrupol mass spectrometer that can be used in tandem as a
GC-MS. The material in the comet 67P/Churyumov–Gerasimenko
was analysed by the Rosetta mission with a chiral GC-MS in
2014.
In
clinical medicine,
dozens
of congenital metabolic diseases also known as inborn errors
of metabolism (IEM) are now detectable by newborn screening
tests, especially the testing using gas chromatography–mass
spectrometry.
GC-MS can determine compounds in urine
even in minor concentration.
These compounds are normally not
present but appear in individuals suffering with
metabolic disorders.
This is increasingly becoming a
common way to diagnose IEM for earlier diagnosis and
institution of treatment eventually leading to a
better outcome.
It is now possible to test a newborn
for over 100 genetic metabolic disorders by a urine
test at birth based on GC-MS.
In combination with isotopic labeling of
metabolic compounds, the GC-MS is used for determining
metabolic activity.
Most applications are based on the
use of 13C as the labelling and the
measurement of 13C-12C ratios
with an isotope ratio mass spectrometer (IRMS); an
MS with a detector designed to measure a few select
ions and return values as ratios.
TOP OF PAGE
and sub-indexes
Key words & phrases: Explaining how to use gas chromatography
and mass spectrometry in tandem - diagram explaining how to connect a gas
chromatograph to a mass spectrometer.
Associated links
mass spectrometry index
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Phil Brown 2000+. All copyrights reserved on revision notes, images,
quizzes, worksheets etc. Copying of Doc Brown's pre-university
advanced level chemistry website material is NOT
permitted. Exam revision summaries & references to science course specifications
are unofficial. These organic chemistry revision notes on
spectroscopy (on the uses and applications of mass spectrometry) suitable for use of pre-university students studying AQA advanced level
chemistry, Edexcel advanced level chemistry, OCR advanced level
chemistry, IB advanced level chemistry, WJEC (Eduqas) advanced level
chemistry, CIE advanced level chemistry, CCEA advanced level chemistry, US grade 11-12 AP honors
chemistry courses and they will also prove useful to
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