1. Elemental Spectroscopy ICP-OES

2. Content: ICP-OES
Fundamentals of ICP-OES
Instrument Components

3. Theory of Inductively Coupled Plasma Optical Emission Spectroscopy

4. ICP is shorthand for ICP-AES or ICP-OES.
ICP Basics
ICP is shorthand for ICP-AES or ICP-OES.
What is ICP-AES? It is:
Inductively Coupled Plasma Atomic Emission Spectrometer.
What is ICP-OES? It is:
Inductively Coupled Plasma Optical Emission Spectrometer.
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5. Atomic Emission Theory
Atomic emission spectroscopy (AES or OES) uses quantitative measurement of the optical emission from excited atoms to determine analyte concentration
Analyte atoms in solution are aspirated into the excitation region where they are desolvated, vaporized, and atomised by a plasma

6. Atomic Emission Theory
Plasma Polychromator Detector
Inductively Coupled Plasma Atomic Emission Spectrometer

7. Excitation
Electrons can be in their ground state (unexcited) or enter one of the upper level orbitals when energy is applied to them. This is the excited state

8. Atomic Emission
A photon of light is emitted when an electron falls from its excited state to its ground state
+ hv
Excited State
Photon
Ground State

9. Element Wavelengths
Each element has a unique set of wavelengths that it
can emit
180nm
<-- uv -->
400nm
<-- visible -->
800nm 1 2 3 4 5

10. Atomic Emission explained
Atomic Emission – the wavelength regions
Lower wavelengths are shorter and have more energy, higher wavelengths e.g. in the Visible region, are longer and have less energy

11. Effect of Temperature on Emission
Wavelength increasing ->
5000 k As Pb Mn Mg Cu Ca Ba Na Li K
3000 k Mg Cu Ca Ba Na Li K
2000 k Ca Na Li K

12. Emission sources Flames Arcs / Sparks Direct Current Plasmas (DCP)
Inductively Coupled Plasmas (ICP)

13. Inductively Coupled Plasma (ICP) – source, plasma formation, plasma zones
Quartz torch surrounded by induction coil
Magnetic coupling to ionized gas
High temperature – equivalent to 10,000k

14. Plasma Advantages
High Temperature – allows for full dissociation of sample components
Argon is Inert – non reactive with sample
Linearity – analysis of samples from ppb to ppm range in the same method
Matrix tolerance – robust and flexible design with Duo and Radial options

15. Plasma Torch

16. Plasma Zones Plasma Zones
observation
region (mm)
TEMPERATURE ~ 2X NITROUS OXIDE ACETYLENE FLAME 25
6000 k 20
6500 k 15
7000 k
RESIDENCE TIME ~ 2MS
8000 k
10000 k
sample

17. Instrument Components
There are six basic components to an ICP
Sample Introduction
Energy Source
Spectrometer
Detector
Electronics
Computer and Software

18. Instrument Components
Sample Introduction
Energy Source
Spectrometer
Computer and Software
Electronics
Detector

19. Instrument Components
Sample Introduction
The sample solution cannot be put into the energy source directly. The solution must first be converted to an aerosol.
The function of the sample introduction system is to produce a steady aerosol of very fine droplets.

20. Instrument Components
Sample Introduction
There are three basic parts to the sample introduction system.
the Peristaltic pump draws up sample solution and delivers it to
the Nebulizer which converts the solution to an aerosol that is sent to
the Spray chamber which filters out the large, uneven droplets from the aerosol.

21. Instrument Components
Sample Introduction
the Peristaltic pump
the Nebulizer
the Spray chamber

22. Concentric Nebuliser

23. Instrument Components
Energy Source
= plasma
The sample aerosol is directed into the center of the plasma. The energy of the plasma is transferred to the aerosol.
The main function of the energy source is to get atoms sufficiently energized such that they emit light.
In the case of commercially available ICP’s, the ionized gas is argon. Helium plasmas are possible but for cost and performance reasons, argon is preferred. It is possible to form plasmas using molecular gases –O2, N2, CO2– but these require huge amounts of energy and can react chemically with the analytes being measured so inert gases are preferred.
Libraries

24. Instrument Components
Energy Source
There are three basic parts to the energy source.
the Radio frequency generator which generates an oscillating electo-magnetic field at a frequency of million cycles per second. This radiation is directed to
the Load coil which delivers the radiation to
the Torch which has argon flowing through it which will form a plasma in the RF field.
In the case of commercially available ICP’s, the ionized gas is argon. Helium plasmas are possible but for cost and performance reasons, argon is preferred. It is possible to form plasmas using molecular gases –O2, N2, CO2– but these require huge amounts of energy and can react chemically with the analytes being measured so inert gases are preferred.
Libraries

25. Instrument Components
Energy Source
the Radio Frequency generator
the Load coil
the Torch
In the case of commercially available ICP’s, the ionized gas is argon. Helium plasmas are possible but for cost and performance reasons, argon is preferred. It is possible to form plasmas using molecular gases –O2, N2, CO2– but these require huge amounts of energy and can react chemically with the analytes being measured so inert gases are preferred.
Libraries

26. Plasma Configuration
Axial
Radial
Axial and Radial

27. Radial or Axial Configuration
Radial design – Robust, fewer interferences
Petrochemical
Metallurgy
Axial design – best sensitivity,
lowest detection limits
Environmental
Chemical

28. Axial Advantage
Much more light available. This gives you the opportunity to achieve Lower Detection Limits than Radial Plasma
BUT- unfortunately, you also get...
More Matrix Interferences
Slightly Reduced Dynamic Range

29. Duo viewing
Axial view plasma looks down the central channel of the plasma, this provides the best sensitivity and detection limits
DUO – this is an axially configured plasma that also allows for radial view through a hole in the side of the axial torch

30. Dual View Optics
Radial view
Axial view

31. Instrument Components
Spectrometer
Once the atoms in a sample have been energized by the plasma, they will emit light at specific wavelengths. No two elements will emit light at the same wavelengths.
The function of the spectrometer is to diffract the white light from the plasma into wavelengths.
Libraries

32. Simultaneous Optics – Echelle Spectrometer
ICP-Source
Detector
Prism
Grating
The iCAP 6000 is echelle spectrometer. A shell spectrometer utilizes a prism and a grating working together To split the spectrum of byte order and wavelengths and end the entire spectrum onto the square or rectangular detector.
This impulse cannot take on this alliance demonstrates the design of the echelle spectrometer.
In the bottom right of the slide you can see the source which in this case is the ICP .
Excited atoms In the ICP emit light at characteristic wavelengths which are focused into the spectrometer.
The limited lights passes through a prism and is reflected off a grating to produce the echelle spectrum.
As I mentioned in the previous slight the echelle spectrum is a square or rectangular shape and can be captured using a detector that matches exactly the shape of the spectrum.
By adopting a national spectrometer design we can use a custom designed solid state detector to analyze the signal .

33. Instrument Components
Spectrometer
There are several types of spectrometers used for ICP. Regardless of type, all of them use a diffraction grating.
For the iCAP, an echelle spectrometer is used. The components in this spectrometer are shown at left.
CID Detector
Focusing
Mirror
Prism
Collimating
Shutter
Slit
(dual)
Echelle grating

34. iCAP Optics - Polychromator
High resolution
200nm
High image quality & low stray light
aberration compensation over whole CID
High energy throughput
double pass prism
All lines on chip
anamorphic magnification
Stable
thermal insulation & heater control to 0.10C

35. Instrument Components
Detector
Now that there are individual wavelengths, their intensities can be measured using a detector. The intensity of a given wavelength is proportional to the concentration of the element.
The function of the detector is to measure the intensity of the wavelengths.
Libraries

36. Charge Injection Device Array Detector
>291,600 addressable silicon-based photo detectors
Full Spectrum Imaging
Random Access Integration (RAI)
Inherently Anti-blooming
Non Destructive Readout (NDRO), allows the S/N ratio to be improved by repeatedly reading each pixel

37. Instrument Components
Detector
The detector is a silicon chip that is composed of many individual photo-active sections called “picture elements”. These picture elements, or pixels, will build up charge as photons impinge on them. Individual pixels are of a size such that they can be used to measure individual wavelengths.
Libraries

38. Emission lines appear as points of light
177 nm
800 nm
740 nm
178 nm

39. Readout Subarray - CID 28 by 28 mm detector element Intensity
Wavelength
28 by 28 mm
detector element

40. What you get
Full, continuous wavelength coverage; never miss an analyte

41. Power and flexibility Rapid qualitative analysis
Ability to analyze for elements in the future without rerunning samples
Fingerprinting
Matrix or spectral subtraction

42. Instrument Components
Electronics
The output from the detector is processed by a set of electronics. The electronics control the detector as well as collect the readings from the pixels
The function of the electronics is to measure and process the output of the detector.
Libraries

43. Instrument Components
Computer and Software
The software, via a computer, controls and runs the instrument. Not only are measurements made but the other five components of the instrument are controlled and monitored by the computer and software,
The function of the computer and software is to operate, monitor, and collect data from the instrument.
Libraries

44. ICP Basics ICP Performance
Typical analysis time for ICP is ~2-3 minutes. This includes flush time, multiple repeats, printing, etc. (Analysis time is independent of the number of elements being determined)
Typical precision, amongst repeats within an analysis, is ~0.5%
Typical drift is ≤ 2% per hour
Typical detection limits are ~ 1-10 parts per billion
Libraries