Working
•In a typicalprocedure, a sample, which may be solid, liquid, or gas,
is ionized, for example by bombarding it with electrons.
•This may cause some of the sample’s molecules to break into
charged fragments. These ions are then separated according to their
mass-to-charge ratio, typically by accelerating them and subjecting
them to an electric or magnetic field:
•Ions of the same mass-to-charge ratio will undergo the same
amount of deflection.
•The ions are detected by a mechanism capable of detecting charged
particles, such as an electron multiplier. Results are displayed as
spectra of the relative abundance of detected ions as a function of
the mass-to-charge ratio.
•The atoms or molecules in the sample can be identified by
correlating known masses (e.g. an entire molecule) to the identified
22.
Detectors
Mass spectrometry detectorsare vital for identifying and
quantifying compounds by measuring their mass-to-charge ratios.
Here are some common types of detectors used in mass
spectrometry:
1.Electron Multiplier Detector (EMD): Amplifies the signal of ions
by converting them into electrons.
2.Faraday Cup Detector: Captures ions directly and measures the
resulting current, providing high accuracy.
3.Photomultiplier Tube (PMT): Converts ions into light photons and
then into electrons for signal amplification.
4.Microchannel Plate Detector (MCP): Uses an array of tiny
channels to amplify the ion signal through secondary electron
emission.
23.
Detector
5.Time-of-Flight (TOF) Detector:Measures the time it
takes for ions to travel a set distance, offering high
mass accuracy.
6.Quadrupole Detector: Utilizes oscillating electric
fields to filter ions by their mass-to-charge ratio.
7.Orbitrap Detector: Traps ions in an electrostatic field
and measures their oscillation frequencies for high-
resolution mass analysis.
8.Ion Trap Detector: Traps ions using electric or
magnetic fields and sequentially releases them for
detection.
Index of HydrogenDeficiency (IHD)
In a hydrocarbon where all the C atoms have only single bonds and no rings are
involved, the compound would have the maximum number of H atoms. If any of the
bonds are replaced with double or triple bonds, or if rings are involved, there would be a
“deficiency” of H atoms. By calculating the index of hydrogen deficiency (IHD), we can
tell from the molecular formula whether and how many multiple bonds and rings are
involved. IHD is also called the Degree of Unstaturation. This will help cut down the
possibilities one has to consider in trying to come up with all the isomers of a given
formula.
Here is a summary of how the index of hydrogen deficiency (IHD) works.
•A double bond and ring each counts as one IHD.
•A triple bond counts as two IHD.
Nitrogen Rule
• Thenitrogen rule states that a molecule that has no or even
number of nitrogen atoms has an even nominal mass whereas a
molecule that has an odd number of nitrogen atoms has an odd
nominal mass.
Time of FlightMS
• Time-of-flight mass spectrometry, commonly known as
TOF MS, is a detection method for gas-phase ions that
determines their mass-to-charge ratio (m/z) based on
measuring how quickly they travel a known distance.
51.
This is acommon form of mass spectrometry, where all particles
of the sample to be analysed are ionised to form 1+ ions.
These 1+ ions are then accelerated to high speeds, deflected
through the spectrometer and then arrive at the detector
As they hit the detector, the mass spectrum graph is produced
The whole of the apparatus is kept under a high vacuum to
prevent any ions that are produced from colliding with
molecules in the air
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Applications
•Environmental monitoring andanalysis (soil, water, and air
pollutants, water quality, etc.)
•Geochemistry – age determination, soil, and rock composition, oil
and gas surveying
•Chemical and Petrochemical industry – Quality control
•Identify structures of biomolecules, such as carbohydrates, nucleic
acids
•Sequence biopolymers such as proteins and oligosaccharides
•Determination of the molecular mass of peptides, proteins, and
oligonucleotides.
•Monitoring gases in patients’ breath during surgery.
•Identification of drug abuse and metabolites of drugs of abuse in
blood, urine, and saliva.
•Analyses of aerosol particles.
•Determination of pesticides residues in food.
