1. Inductively Coupled Plasma
ICP OES/MS
Inductively Coupled Plasma
Optical Emission Spectrometry
&
Mass Spectrometry
Nima yadollahi
Postgraduate Student (MSc)
Materials Science Engineering
Corrosion & Protection of materials

2. Introduction:
Electrons of an atom absorb energy and jump to higher energy levels
When they return to normal states, they emit characteristic photons of energy.
By isolating these photon wavelengths, we can determine the types and
concentrations of the elements present.

3. Atomic spectrometry Atomic Absorption Atomic Emission
Light of specific characteristic wavelength is absorbed by promoting an electron to a higher energy level (excitation)
Light absorption is proportional to
elemental concentration -
Light of specific wavelength
from Hollow Cathode Lamp (HCL)
Atomic Emission
High energy (light and heat) promotes an electron to a higher energy level (excitation). Electron falls back and emits light at characteristic wavelength
Light emission is proportional to
elemental concentration -
Light and heat energy from high intensity source (flame or plasma) - -
Mass Spectrometry -
High energy (light and heat) ejects electron from shell (ionization). Result is free electron and atom with positive charge (Ion)
Ions are extracted and measured directly in mass spectrometer
Light and heat energy from high intensity source (plasma)

4. Crucial steps in atomic spectroscopies and other methods
Laser ablation ,etc.
M+ X-
MX(g)
Nebulisation
Solid/liquid sample
Solution
Molecules in gas phase
Desolvation
Sample
preparation
Vaporisation
Sputtering, etc.
M(g) + X(g)
Atomisation=Dissociation
Atoms in gas phase
Ionisation
Excitation M+
Ions
Excited Atoms
 ICP-MS and other MS methods
 AAS and AES, X-ray methods
Adapted from (Gary Hieftje)

5. Atomisation / Ionisation
In plasma, sample moves through several zones
Preheating zone (PHZ): temp = 8000 K: Desolvation/evaporation
Initial radiation zone (IRZ): K: Vaporisation, Atomisation
Normal analytical zone (NAZ): K: Ionisation
Start gas flow
Switch on RF power
Ionisation of argon gas
After leaving injector, sample moves at high velocity Punches hole in centre of plasma
Plasma generated

6. Viewing position of plasma
The plasma generated in an ICP can be viewed by the spectrometer,side-on or end-on. These viewing positions are called radial and axial viewing, respectively
Radial: light emitted from analyte has to pass only a short distance in plasma
i.e. less chance of self absorption and better for concentrated samples.
Axial: direct view into plasma, lower sensitivity, shifts detection range lower.

7. Nebulizer & Spray Chamber
Diagram of a Pneumatic Concentric Nebulizer.
Diagram of a Pneumatic Babington Nebulizer.
Diagram of a Pneumatic Cross-Flow Nebulizer.
Typical spray chambers used with ICP-OES. A - Scott double pass type, B - conical single-pass type with impact bead. A B

8. Overview of a Basic Inductively Coupled Plasma Atomic Emission Spectrometry
Demountable ICP Torch.

9. Types Of Spectrometers / ICP OES
There are several devices available:
Monochromators
(only isolate one line at any given instant)
Polychromators
Echelle spectrometer
(Interrogate several different lines simultaneously)
monochromators
Rowland circle (polychromators)
ICP source
Diffraction grating
Lens
Detectors
Exit slits
Echelle cross disperser (polychromator)

10. layout of a photomultiplier tube
Spectrometers
layout of a photomultiplier tube
(PMT)
Diffraction Gratings
Diffraction Grating is a mirrored surface that has closely spaced lines ruled or etched onto its surface.
The continuum light that hits the grating will be diffracted at an angle that is dependent upon the wavelength. nλ = 2dsinθ Bragg's Law
Most spectrometers use diffraction gratings to achieve dispersion.
Photocathode, dynode and anode

11. Sample preparation
Salt Fusions – typically lithium metaborate LiBO2 and sodium peroxide Na2O2.
Sample is mixed with lithium metaborate in a 1:9 ratio.
Mix is melted at 900C and dissolved in a nitric acid solution.
Acid Digestions – nitric HNO3, hydrochloric HCl, perchloric HClO4 and hydrofluoric HF, acid.
Certain materials require digestion in conc. HF.
Br2 or H2O2 can be added to conc. acids to give a more oxidising medium and increase solubility.
Sample is allowed to dissolve in an acid mix.
Sample is typically heated to speed dissolution.
Microwave Digestion – basically acid digestion in controlled temperature and pressure vessels.
Sample is allowed under controlled temperature and pressure conditions in a pressure vessel.
Graphite crucible with lithium metaborate in furnace
Acid digestion in a Pt dish
Rotor

12. Calculations
%E =[(Result ppm x dilution) / Sample ppm] x 100

14. Elements by ICP-OES
Different elements have different emission intensities.
e.g. Alkalis (Na, K, Rb, Cs) are weakly emitting.
Alkaline Earths (Be, Mg, Ca, Sr, Ba ) are strongly emitting.

15. Detection Limit / ICP-OES (ppb - μgr/Lit)
Common Problems in ICP-OES
Sampling and Sample Preparation
Spectral Interference
Matrix Effects
Instrumental Drift

16. Schematic diagram of an ICP-MS instrument
Mass analyzer
Lens optics
ICP torch
Detector
RF generator
Sampler cone
Nebulizer and spray chamber
Skimmer cone
Turbomolecular pump
Mechanical pump

17. ICP-MS - Ionization + Analyte present as M+ ions
Aerosol is dried
Particles are decomposed and dissociated
Atomized and then ionized
Analyte present as M+ ions
Highest M+ population should correspond to lowest polyatomic population
Hottest part of plasma is ~8000K
Sample channel is ~6700K

18. Inductively Coupled Plasma Mass Spectrometry
Mass spectrometry method:
Detects ions distinguished by their
mass-to-charge ratio (m/z value)
Based on ions moving under influence of electrical or magnetic field
Mass analysers generally require operation under vacuum, to avoid ions colliding with other particles

20. ICP-MS – Interface (Ion Focusing)
Focusing lens:
+ve charged metallic cylinder which repels ions and refocus the ion beam. It Requires optimization.
Grounded Shadow Stop:
Traps photons and unionized materials from the plasma

21. ICP-MS – Mass analyzer (quadrupole)
Four short, parallel metal rods are arranged symmetrically around the ion beam.
DC and AC electrical potential is applied to the rods with opposite rods having a net negative or positive potential.
The combined field causes the ions to oscillate about their central axis.
Only those isotopes with certain mass to charge ratio can pass through the array without being removed.
+ d.c. -
+ a.c. -
m/e = H2 r2 / 2v

22. ICP-MS – detector Electron Multiplier (EM) Dynode
Electrons
Ion M + e -
Fast analogue detection
Pulse counting detection
Ion striking the 1st dynode causes the release of e- from the dynode surface. These e- are attracted to the 2nd dynode causing further release of e- and so on down the multiple detector dynodes.

23. Analysis using ICP-MS – interferences
Isobaric Interference
“Isobaric overlaps” produced by different isotopes of other elements in the sample that create spectral interferences at the same mass as the analyte.
Matrix effect
The signal of the analyte suppressed by the matrix component. There are basically two types of matrix induced interferences.
Analyte
Interference
39K+
38Ar1H+
40Ca+
40Ar+
51V+
35Cl16O+
52Cr+
40Ar12C+
56Fe+
40Ar16O+
63Cu+
23Na40Ar+
75As+
40Ar35Cl+
80Se+
40Ar2+
Sample transport effect
Impact on ionization temperature of the plasma
Polyatomic interference
Interferences arising from the component of the plasma and the sample matrix. For example, Cl- in sample matrix interferes with 75As by 40Ar35Cl+

24. Principles of Dynamic Reaction Cell (DRC)
sampler
skimmer
lens
reaction cell
mass analyzer
vent
Polyatomic interference can be eliminated by DRC method.
DRC is a quadrupole placed inside an enclosed reaction chamber. This enclosed quadrupole is positioned between the ion optics and the analyzer quadrupole. A reaction gas such as NH3, CH4, H2 and He2 is used to pressurize the reaction chamber to eliminate the interference by either to:
convert interfering ions into new polyatomic species which no longer interfere; or
convert the analyte ion to a new polyatomic species at a new m/z ratio which is not interfered

25. Ion-molecule reactions and collisions
Example of ICP- DRC –MS
Reactive Fill Gas Inlet (NH3)
Quadrupole Ion
Guide Control Ar + + + +
50Ar16O+ + + + + + +
56Fe+
Quadrupole + +
56Fe+ + + =
Isobaric
Ion-molecule reactions and collisions
NH3+ O
ArO+ + NH3
O + Ar + NH3+

26. Principles of Octopole Reaction System (ORS)
The stainless steel ORS cell, which can be pressurized with a gas, typically hydrogen or helium, is positioned between the ion lens assembly and the quadrupole mass filter. As analyte ions enter the cell, they interact with the gas, resulting in the reduction of the molecular interference .
Hydrogen mode:
Charge transfer: Ar+ + H2  H2+ + Ar
Proton transfer: ArH+ + H2  H3+ + Ar
Helium mode:
CID: When the collision energy between the He atom and polyatomic ion is significantly above the dissociation energy of the polyatomic ion, fragmentation occurs.
ED: the larger polyatomic species collide more frequently with the cell gas, so they lose more energy than the smaller analyte species. The cell acts as a molecular filter by resolving low energy (polyatomic) and higher energy (analyte) ions from each other in the ion beam.

27. ICP-MS System with Collision Reaction Cell (CRC)
Multi-element interference removal by on-axis octopole reaction cell
Fast simultaneous dual mode detector
Reaction Gas Inlet
High temperature 27MHz plasma generator
Plasma
Octopole
Off-axis Lens
High frequency hyperbolic quadrupole
Low flow sample introduction system

28. Typical detection limits of ICP-MS instrument

29. Price/Performance – How does ICP-MS Compare With Other Inorganic Techniques ?
200
Inductively Coupled Plasma Mass Spectrometry (Quadrupole)
Typically 1ppt to 100ppm
150
Typical price range US$k
Inductively Coupled Plasma Optical Emission Spectroscopy
Typically 1ppb to >1000ppm (Simultaneous)
100
Graphite Furnace Atomic Absorption Typically 10ppt to 100ppb 50
Flame Atomic Absorption
Typically 50ppb to 500ppm
1ppt
10ppt
100ppt
1ppb
10ppb
100ppb
1ppm
10ppm
100ppm
1000ppm
Typical measurement range

30. ICP-OES Advantages Disadvantages multielement, fast
flexible element selection
well documented methods
very good tolerance to dissolved solids
good linear dynamic range
Disadvantages
relatively poor detection limits
many spectral interferences
sample consumption high (1 to 5 mL/min)

31. ICP-MS Disadvantages Advantages
excellent detection limits for most elements (ppb - ppt)
most elements in Periodic Table available
good sample throughput
much simpler spectra than optical techniques
low sample volume consumption
mass spec - so isotopic information available
Disadvantages
dissolved solids/matrix effects - need to dilute samples more than other techniques
capital cost high
requires knowledgeable operator

32. Some websites for ICP-AES and ICP-MS:
and

33. the end !!