Trace element analysis of
geological materials by ICP-MS I
DSP analytical geochemistry
Markéta Holá, MU Brno
Tento učební materiál vznikl v rámci projektu Rozvoj doktorského studia chemie
č. CZ.02.2.69/0.0/0.0/16_018/0002593
C9067
Outline
1. Mass spectrometry. General introduction and history.
2. Ion sources for mass spectrometry. Inductively coupled plasma.
3. Interface. Ion optics. Mass discrimination. Vacuum system.
4. Spectral interferences. Resolution, ion resolution calculations.
5. Mass analyzers. Elimination of spectral interferences.
6. Non-spectral interference.
7. Detectors, expression of results.
8. Introduction of samples into plasma.
9. Laser ablation for ICP-MS.
10.Excursion in the laboratory.
“The basic principle of mass spectrometry (MS) is to generate ions from either inorganic or organic
compounds by any suitable method, to separate these ions by their mass-to-charge ratio (m/z) and
to detect them qualitatively and quantitatively by their respective m/z and abundance…“
(Kienitz, 1968)
Mass Spectrometry
basics
It follows directly from this definition that atoms or molecules need to carry an electric charge, i.e.,
they need to be transformed into ions, for MS to work.
Mass Spectrometry
basics
WHY IONS?
The electric charge acts like a handle that allows to grab these atoms or molecules. In
contrast to neutrals, ions can be accelerated and decelerated, can be shot into defined orbits
or other flight paths, and can finally be collected and detected. The “race tracks” of these ions
can be determined by application of electric and/or magnetic fields. While the Coulombic force is
exerted on ions in electric fields, the Lorentz force influences ions moving with a component
orthogonal to the magnetic field.
Mass Spectrometry
basics
Moving of particles in an electric field
+
++
-
The electric (Coulomb) force Fel exerted
by the field on the positive charge is:
𝑭 𝒆𝒍 = 𝒒 𝑬 =
𝒎 𝒗 𝟐
𝒓
q charge magnitude
E electric field (N·C−1; V·m−1)
m mass (kg)
v velocity (m·s−1)
r radius of the ion path
𝒓 =
𝒎 𝒗 𝟐
𝒒 𝑬
+ +
Mass Spectrometry
basics
Moving of particles in a magnetic field
++ -+ +
x x x x x x
x x x x x x
x x x x x x
x x x x x x
x x x x x x
Magnetic field going into the page
From north to South
The magnetic (Lorentz) force Fmag
exerted by the field on the positive
charge is:
𝑭 𝒎𝒂𝒈 = 𝒒 𝒗 𝑩 =
𝒎 𝒗 𝟐
𝒓
q charge magnitude
B magnetic induction (T; kg·s−2·A−1)
m mass (kg)
v velocity (m·s−1)
r radius of the ion path
𝒓 =
𝒎 𝒗
𝒒 𝑩
Mass Spectrometry
basics
𝒓 =
𝒎 𝒗
𝒒 𝑩
𝒓 =
𝒎 𝒗 𝟐
𝒒 𝑬
q ("quantum") is used as symbol for the electric charge, while z is used as unit for
the charge number, e.g. 1, 2, -1, -2 etc.
𝒎
𝒛
Ions can be separated due to the mass-to-charge ratio
𝒎
𝒛
= 50……..
𝟏𝟎𝟎
𝟐
𝐨𝐫
𝟓𝟎
𝟏 …the same separation for different analytes.
(dimensionless quantity)
Mass Spectrometry
basics
Mass number=(# protons)+(# neutrons)
1 AMU = 1 mu = 1 Da = 1.66053904020 x 10-27 kg
AMU atomic mass unit - It is a unit of mass used to express atomic or molecule
masses. When the mass is expressed in AMU, it roughly reflects the sum of the
number of protons and neutrons in the atomic nucleus (electrons have so much less
mass that they are assumed to have a negligible effect).
Mass number vs. Atomic mass unit
Mass number - also called atomic mass number or nucleon number, is the total
number of protons and neutrons (together known as nucleons) in an atomic nucleus.
56Fe amu 55.9349363
Mass number
mu = m(12C)/12
Mass number vs. Atomic mass unit
56Fe+
40Ar16O+
AMU: 40Ar16O 55.957 vs. 56Fe 55.935 It is possible to distinguish!
AMU: 40Ar 39.96238312 vs 40Ca 39.9625909 No mass spectrometer has sufficient resolving power!
number of protons and neutrons (mass number) 56, charge number is +1
𝒎
𝒛
= 56
Mass Spectrometry
in general
• Analytical method
• works with the resolution according to the m/z ratio, where m is the
mass and z is the charge of the fragment-ion (molecule, part of the
molecule, atom)
• determination of molecular weight, elucidation of chemical structure
of peptides or other organic compounds, determination of elemental
composition of sample
• the principle of mass spectrometry is based on ionization of molecules
or atoms, their subsequent separation by m/z and detection
Mass Spectrometry
of organic compounds
• structural analysis
• identification of substances
Mass Spectrometry
of organic compounds
Different compounds can be uniquely identified by their mass
CH3CH2OH
N
OH
HO
-CH2-
-CH2CH-NH2
COOH
HO
HO
Butorphanol L-dopa Ethanol
MW = 327.1 MW = 197.2 MW = 46.1
Mass Spectrometry
inorganic
• elemental trace analysis
• isotopic ratio – radiometric dating
• elemental imaging
Mass Spectrometry
in general
The first mass spectrometer - originally called a parabola spectrograph - was constructed in 1912 by J.J.
Thomson, best known for his discovery of the electron in 1897. He used the mass spectrometer to
uncover the first evidence for the existence of nonradioactive isotopes. His device for the
determination of mass-to-charge ratios of ions was based on turn-of-the-century research on
kanalstrahlen, the streams of positive ions formed from residual gases in cathode ray tubes, initially
found emitted from channels cut in the cathode plate. Local magnetic and electrostatic fields deflected
these positive rays depending on their mass, resulting in diverging traces on a photographic plate.
Mass Spectrometry
history
Glow
discha
rge
hollowcathode
magnet+
electrodes
vacuum pump
photographicplate
glow
discharge
in Ne
In following decades, the development of mass spectrometry continued (Aston, Dempster, Bainbridge,
Nier and others), initially for the purpose of discovering new stable isotopes, determining their
representation and exact atomic weight, even before the second world war this technique was used in
the study of metabolism.
In the 1940s, mass spectrometry was used in the military as part of the "Manhattan" project in the
production of the atomic bomb and as an analytical tool in monitoring the products of the oil industry,
which in the following years it started commercial production mass spectrometers, especially in the
sector arrangement. Principles of TOF analyzers, ion cyclotron resonance and quadrupole analyzer
were described in 1946-1953 and these instruments were also subsequently marketed, although not
always initially successfully.
Mass Spectrometry
history
Mass Spectrometry
history
The combination of mass spectrometry with gas chromatography in the 1960s and with liquid
chromatography in the 1970s, it heralded a wide use in the multicomponent analysis of complex
mixtures of organic substances. The possibilities of tandem arrangement for quantitative analysis were
also discovered during this period. Main however, the problem lay in the limited possibilities of
ionization techniques, when the problem was, for example, the ionization of very polar substances or
biomacromolecules. The breakthrough was the introduction of ionization using electrospray or MALDI
in the 1980s, which widened the applicability mass spectrometry for the indicated types of
compounds.
Mass Spectrometry
history
https://link.las.iastate.edu/2018/04/20/setting-a-standard-for-security/
Houk devised, demonstrated and improved an experiment
called inductively coupled plasma mass spectrometry (ICPMS),
which can distinguish and measure even trace levels of
elements like lead in a sample. No other method can
measure such a low of concentration of elements.
Sam Houk discovered papers from Alan Gray’s research at
the Applied Research Laboratories in England. Gray was
experimenting with mass spectrometry using a different
plasma source, which sparked Houk’s idea of using
inductively coupled plasma for mass spectrometry. He
would just need to build instrumentation that could extract
the atoms from the plasma for analysis by the mass
spectrometer.
In 1977, Houk built the first functional model of
an ICP-MS spectrometer, which was a significant
advancement in combining plasma technology
with mass spectrometry. This spectrometer was
named the "Plasma-Mass Spectrometer".
Mass Spectrometry
history
Mass Spectrometry
history
"NOAA's "PALMS" instrument aboard the NASA WB-57
high-altitude research aircraft. The Particle Analysis by
Laser Mass Spectrometry instrument characterized the
chemical composition of seeds in individual cirrus
crystals sampled during several research flights over
North America and Central America."
https://commons.wikimedia.org/wiki/File:WB-57_PALMS_Mount.jpg
Replica of Francis William Aston's third mass spectrometer.
Inductively Coupled Plasma Mass Spectrometry, www.thermofisher.com
Mass Spectrometry
history
The first mass spectrometer in Czech Republic (ČSSR) – construction by V. Čermák, V. Hanuš, Č. Jech, J.
Cabicar in 1953 at Institute of Physical Chemistry and Electrochemistry of the Czechoslovak Academy of
Sciences (ČSAV).
Chem. Listy 104, 955-990 (2010)
Founders of MS in the Czech Republic:
RNDr. Vladimír Hanuš, CSc. (1923-2009) and
RNDr. Vladimír Čermák, DrSc. (1920-1980)