Inductively coupled plasma mass spectrometry (ICP-MS) allows for analysis of elements at very low concentrations. It works by ionizing analyte atoms from liquid samples using plasma and then detecting the resulting ions using a mass spectrometer. ICP-MS provides high sensitivity, accuracy, and a wide linear dynamic range. It has numerous applications including environmental analysis, clinical analysis, and analysis of geological and metallurgical samples. The key components are the inductively coupled plasma ion source, interface between the plasma and mass spectrometer, quadrupole or time-of-flight mass analyzer, and detector.

1. Inductively Coupled Plasma
Mass Spectrometry ((ICP-MS)

2. Mass Spectrometry
• Mass spectrometry (MS) is similar to NMR in that it has historically been of great value in
structure elucidation of relatively small organic & biomolecules.
• MS analysis of proteins & other biopolymers was initially hindered because analytes are
usually measured in the gas phase.
• The development of new methods now makes it possible to study large molecules i.e.
sample preparation (ionization)
multiquadrupole analysis
tandem MS instruments
powerful computers

3. Ionization and Analysis of Proteins
• Mass spectrometer generally consists of three components (figure 7.17).
ionization device
mass analyzer
ion detector
• Neutral molecules are ionized, & their positively charged ion products are directed through an
electric and/or magnetic field, and separated on the basis of mass-to-charge ratio (m/z).
• A detector then records the ions after separation.
• The “spectrum” generated by MS displays ion intensity as a function of m/z.

8. multiquadrupole
analysis

11. Continue……..
• Ionization of small organic & biological molecules is done by electron impact while
nonvolatile & biological macromolecules requires special treatment.
• In the late 1980s, “soft ionization” method was introduced for the macromolecules.
• Electrospray ionization (ESI) involve spray of sample’s solution via a metal needle or
capillary tip held at a potential (+ 5000 V) that results in tiny droplets (+ve ions)
• Solvent evaporates, and ions are directed into the analyzer for separation.
• Pulses from N2 laser used to ionize proteins from surface (soft laser desorption; SLD)
• Both ESI & SLD are liquid-phase processes hence require purified samples

12. Electrospray ionization (ESI)

13. • Laser desorption has been modified to a solid phase method, matrix-assisted laser
desorption ionization (MALDI), widely used technique for protein analysis.
• In MALDI, sample is placed in matrix of small organic molecules & irradiated by laser pulse.
• Matrices absorb laser energy, causing ionization of macromolecular sample.
• Several types of mass analyzers are used for ion separation, including time-of-flight (TOF),
quadrupoles, and ion traps.
• The TOF-MS is most widely used technique in which each ion produced has same initial
kinetic energy, but speed varies with mass.
• Mass is determined by measurement of an ion’s time-of-flight to detector.
Continue……..

14. time-of-flight (TOF)

15. MS Applications in Biochemistry
• MS, becoming a standard tool in the analysis of biological molecules and biological
processes i.e.
• Identification of peptides & proteins
Identification of proteins is widely done by MS.
important ions resulting from the removal of an electron by ionization procedures are
+ ve charged molecular ions (m+) or protonated molecular ions (m+nh)n-1.
measurement of molecular mass provides the molecular weight of original molecule.
the accuracy of this method for molecular weight determination is about 0.01%.

16. some molecular ions are unstable & disintegrate to produce fragment ions.
these fragmentation processes are useful in structural elucidation of smaller molecules.
• One MS method for peptide identification is called peptide mass fingerprinting.
unknown sample is digested with trypsin to produce fragments & analyzed by MALDI-MS.
resulting spectrum displays the masses of peptide fragments.
used as a “fingerprint” of sample & compared with known fragmented patterns in a
sequence database.
Continue……..

17. • Characterization of post-translational modification processes
after translation, proteins are often modified by covalent attachment of specific functional
groups like
Phosphorylation
Glycosylation
these chemical modifications can easily be detected by MS
Continue……..

18. • Peptide Sequencing
small peptides & proteins may be sequenced by MS procedures.
the peptide sample is ionized & fragmented at the peptide bonds by collision-induced
dissociation.
size analysis of the series of fragments produced leads to the sequence of amino acids.
Continue……..

19. • Protein-protein interactions
most important goal of proteomics is to study how proteins interact with each other.
ESI-MS and MALDI-TOF are currently being used to investigate how proteins associate
to form biologically active multi subunit complexes.
Continue……..

20. ICP-MS
• The inductively coupled plasma (ICP) & the quadrupole mass analyzer caused an increase
in the use of atomic MS as an analytical tool.
• ICP-MS permits determination of most of elements at very-low-concentration levels.
• It has great advantages over other techniques for elemental analysis as it used to
determine most elements at high sensitivity & at a wide range of concentrations.
• Moreover, isotope ratios can be obtained, providing geochemical & geochronological
information.

21. • There are several properties of MS as an analyzer & the argon ICP as an ionization
source make ICP-MS an attractive combination.
• The ICP has a high ionization efficiency & it produces mainly singly charged +ve ions.
• Hence, mass spectra are very simple & elements are easily identified and the isotope
ratios can be easily measured.
• Moreover, the mass spectrometer is very sensitive, with detection limits up to three
orders of magnitude better than ICP-OES.
• And is linear over a wide dynamic range of up to five orders of magnitude.
• Table 10.21 presents some aspects of ICP-OES & MS that complement each other.
Continue……..

23. • The instrument is an ICP interfaced with a quadrupole MS as shown in figure 10.36a.
• This ICP source is horizontal, with argon plasma concentric to the mass spectrometer
inlet.
• Figure 10.36b shows the layout of a new ICP-MS, the Perkinelmer nexion 300, with the
plasma vertical to the mass spectrometer.
• This instrument has a quadrupole ion deflector (QID) above the torch.
• The QID turns positively charged ions from the plasma 90° to the left, into the mass
analyzer, while nonionized material flows straight up & out of the system.
Instrumentation

25. • While the instrument has a QID & a quadrupole reaction cell, it has only one analyzing
quadrupole
• ICPS operate at atmospheric pressure & at a temperature of about 10,000 k.
• While, the MS requires a high vacuum (10−4–10−6 torr) & operates at room
temperature.
• Most ICP-MS systems have an interface similar to the one shown in figure 10.37, but the
nexion 300 shown in figure 10.36b has three cones.
• In figure 10.37, the argon ICP plasma is on the right side of the diagram.
• Ions from the plasma enter into mass spectrometer through a two-stage interface.
Continue……..

27. • Plasma is centered on sampler cone, & ions & plasma gas pass through the orifice in
the cone into a vacuum-pumped region.
• Most of argon gas is pumped away in this region.
• The remaining ions pass through the skimmer cone into the mass spectrometer.
• The design of this cone restricts the flow of ions into the mass spectrometer to the
central part of the flow initially coming from plasma.
• Region behind the skimmer cone is evacuated to a pressure of about 10−4 torr by a
turbomolecular pump.
• This region can be isolated from the higher pressure of the interface region by a gate
valve
Continue……..

28. • This permits the sampler & skimmer cones to be removed for cleaning without breaking
the vacuum in mass spectrometer.
• Both sampler & skimmer cones are made of either nickel or platinum & are water cooled
by contact with water flowing within the interface chamber.
• The hyper skimmer cone in the perkinelmer instrument is designed to focus the ions
even more tightly, with the aim of increasing stability & eliminating drift.
• Series of ion-focusing elements similar to those developed for double-focusing mass
spectrometers have been utilized to introduce the ions into the quadrupole.
Continue……..

29. • Interference effects due to the presence of large numbers of photons reaching detector
are eliminated by photon stops in older designs or off-axis ion lenses in newer one
• Background signals have been largely eliminated in modern ICP-MS instruments.
• Other mass analyzers are used with ICP ionization source, including high-resolution
magnetic sectors & TOFS.
• ICP-TOF mass analyzer systems as well as other designs have advantage of
simultaneous measurement of ions.
• Simultaneous measurement is critical for accurate determination of isotope abundances
as well as for accurate quantitative work using isotope dilution.
Continue……..

30. Applications of Atomic MS
• ICP-MS is particularly useful for rapid multi element determination of metals &
nonmetals at concentrations of ppq, ppt, and ppb.
• Only unit mass (low) resolution is required to discriminate between different elements,
as isotopes of different elements differ by 1 unit mass.
• There are only a few isotopic overlaps between elements, so one can usually find an
isotope to measure for any given element.
• The applications discussed are from many forms of atomic MS, including ICP-MS,
GDMS, and coupled chromatography-ICP-MS.

31. • Uses for ICP-MS include analysis of
environmental samples for ppb levels of trace metals & nonmetals.
body fluids for elemental toxins such as lead & arsenic
trace elements in geological samples, metals & alloys, & isotope ratios
Analysis of ceramics, semiconductors, pharmaceutical, forensic & cosmetic samples
Determination of platinum group catalysts in polymers, elemental analysis in petroleum
& chemical industries
Metal determinations in clinical chemistry & food chemistry.
Applications of ICP-MS

32. • Most common samples analyzed by ICP-MS are aqueous solutions.
• Sample is dissolved in acid, digested or fused in molten salt, & then diluted to desired
volume with water.
• All reagents must be of extremely high purity, given the sensitivity of the ICP-MS
• Aqueous solution is introduced into plasma using a peristaltic pump, nebulizer, & spray
chamber system.
• Solid samples can be analyzed by laser ablation ICP-MS or by coupling an electrothermal
vaporization (ETV) or electrothermal atomizer (ETA) to the ICP-MS.
Analysis of Sample

33. • Solids can also be analyzed by GDMS and spark source MS.
• Laser ablation ICP-MS can measure elements in fluid inclusions in rocks, microscopic
features in heterogeneous materials, & individual crystals in samples like granite.
• It can be used for analysis of artworks & jewelry.
• Quantitative analysis by ICP-MS is usually done with external calibration standards &
the addition of internal standards to all standards & samples.
• For determination of large number of elements, it is usual to add Li, Y, In, Tb, and Bi &
measure the ions 6Li, 89Y, 115In, 159Tb, and 209Bi as internal standards.
Continue……..

34. • Internal standard that is most closely matched in first ionization potential to the analyte is
generally used.
• Results obtained using this approach are generally very accurate & precise.
• Table 10.23 presents typical spike recovery & precision data for ICP-MS determination
of 25 elements in a certified reference material (crm) “trace elements in drinking water”
from high-purity standards, Charleston, SC
Continue……..

36. Recommended book
Biochemistry Laboratory: Modern Theory and Techniques
Rodney Boyer (Hope College)
Second Edition
Chapter 7: Spectroscopic Analysis of Biomolecules (D.
Mass Spectrometry)
Undergraduate Instrumental Analysis
James W. Robinson (7th Edition)
Chapter 10: Mass Spectrometry II: Spectral Interpretation and
Applications (10.4.1 ICP-MS)