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Elemental
OES Basics
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Informations OES
Basics of OES Instrumentation Calibration
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Basics of OES
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Historical Overview
17th century (1666–1672): Isaak Newton
1. Prism
Spectral colors
2. Prism
white light
Sunlight
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Historical Overview
Isaak Newton: Christiaan Huygens:Light = Particle radiation Light = Wave phenomenon
(like sonic waves)
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Historical Review
1887: Heinrich Hertz
Light = Small part of the electromagnetic spectrum
1905: Albert Einstein
Light = Particles (Photons)
The 1921 physics Nobel prize was awarded to Einstein in most famous for his theory of relativity, but it is his discovery of photons that is mentioned by the Swedish Academy.
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Historical Review
Both is true:
Light behaves somtimes like a Wave,and sometimes as a Particle !
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Historical Review
1860: R. W. Bunsen and G. R. KirchhoffExistence of colors in flames =Processes in the atomsDifferent sort of atoms = Different colors in flames
Foundation Stone for the Spectral Chemical Analysis
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Basics OES
In the
Optical Emission Spectroscopy,
the atoms are exited by heat from an electrical discharge. The arising light is being dispersed into spectral wavelengths and the intensity of specific, atom related lines is measured.
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Basics OES
Atomic structure Niels Bohr theory
The atomic nucleus contains protons (+) and neutrons (). In special orbits electrons (-) are moving around the nucleus.
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Basics OES
If enough energy is transferred to the atoman electron can be moved from one orbit (shell) to a higher on. It is now in an “exited“ status
Energy transfer
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Basics OES
The electron´s position is not stable as long there is an unocupied position in an lower orbit. It falls back in a lower orbit. It must now get rid of the energy it got to move from a lower to a higher orbit. This is done by emitting light (Photons).
Radiation
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Basics OES
Wavelenghts and -ranges
Units 1 nm = 10-9 m 1 Å = 10-10 m
Ranges Infrared range > 800 nm...
Visible range: 400-800 nmUV-range: 200-400 nmVUV-range < 200 nm...
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Gamma- X- UV visible Infrared Radio-rays rays Spectrum
0.01 nm 1 nm 100 nm 400-800 nm 1 mm 1m 1 km
Basics OES
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Basics OES
Depending on the different possibilities of electron transfer between shells there are several specific wavelenght for an atom.
The OES uses the wavelength range 120 - 800 nm
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Atomic lines• Exitation of electrons in neutral atoms
Ionic lines• Exitation of electrons in an ion (ionized Electron)
(atom which lost one or more electrons)
Basics OESAtomic lines and Ionic lines
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Instrumentation
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Video Automatic system with grinding
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Spark Stand with sample
Keyboard, Mouse, Printer(PC not visible)
Instrumentation I
Sample Clamp
Start/Stop ButtonInstrumentation
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Vacuum Tank
Source Box
Read-out & Source Controller
Integrator Boards
Air ConVacuum Pump
Spark Stand
Power Supplies
Not visible:Personal ComputerKeyboard, Mouse, PrinterSoftware Package
Argon Block
Instrumentation II
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Instrumentation
Main components are:
- Exitation system- Optical system- Readout system- Computer
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Instrumentation
Components:
Exitation system Optical system Readout
Computer Printer
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Instrumentation
Exitation system:
- Between electrode and sample surface an electrical discharge is established- Material is being evapourated, partly atomized or ionized. - Atoms and ions are exited
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Digital generation of any current supply curves with max. 250 A peak current
Discharge 10 µs to 2 ms Max. 1000 Hz spark frequency
Instrumentation Exitation Source
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Optical System:
- The exited light from the exitation source is transfered into the optical system- It is dispersed into the wavelengths contained in the exited light- The intensity of the atom dependend wavelenght is measured.
Instrumentation
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CPM detector
CPM detectors
Rowland Circle
sample
Instrumentation
Electrode
CPM detector
Entrance Slit
Grating
Exit Slit
Exit Slit
Exit Slit
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Instrumentation
OPTIC
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Optical System:
Grating and slits are mounted on a circle (Rowland circle), which diameter equals the concave radius of the grating. The spectral lines are images of the entrace slit on the position of a specific wavelength. They exist exactly on the Rowland circle.(Paschen Runge mounting)
Instrumentation
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Instrumentation
Optical System:
- The entrance slit width is usually 10 µm, its hight up to 20 mm.
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Optical System
Grating:
As dispersive medium a concave grating between 1800 and 3600 groves/mm is used. The light is dispersed and reflected on the surface of this grating.
Instrumentation
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Direct lightpath
Grating
Entrance slit
Exitslits and CPMs
HV
Connection toreadout system
Instrumentation
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Instrumentation
Channel - Photomultiplier (CPM) Since 1995 on the market Developed and produced in Germany Compact High sensitivity High dynamic range Extrem low dark current High amplification Wavelenght coverage: 110-850 nm
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Photomultiplier:
CCD Detector (Charged Coupled Device)
Both detectors convert light into an electrical signal (current).
Instrumentation
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CCD (Charged-Couple-Device)
CCD detectors known from scanners and bar code readers or Cameras
Function based on semiconductor Technology Cheap detector Developed in early 1970‘s
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CCD (Charged-Couple-Device)
CCD Basics CCD imaging is performed in a three-step process:
1. Exposure, which converts light into an electronic charge at discrete sites called pixels 2. Charge transfer, which moves the packets of charge within the silicon substrate 3. Charge-to-voltage conversion and output amplification.
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CPM (Channel-Photo-Mulitiplier)
© graphics by Olympus Microscope & Perkin Elmer optoelectronics37
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Wavelenght 1st order
Used CPM
Used Filter
Wavelenght 2nd Order
Used CPM
Used Filter
800nm-580nm 963 GG475
580nm-540nm 934 GG475 414nm-330nm 934
540nm-317nm 934 330nm-317nm 934 UG5
317nm-210nm 933 317nm-250nm 933 UG5
210nm-162nm 932 250nm-165nm 922
165nm-120nm 911 165nm-120nm 911
Instrumentation CPM at Bruker Elemental OES
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Developed by Bruker (Quantron) and Perkin Elmer
Optimized on CPM detectors
Frequency up to 250 kHz
Single Spark Evaluation(only with CPM)
Time Resolved Spectroscopy with up to 4 windows in any source parameter (only with CPM)
Instrumentation Readout
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Instrumentation
Readout system:
CPM/CCD Integrator ADC PC
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Instrumentation
Instrument to measure intensities of light
- up to now the described instrument is able to measure intensities of light emitted by the source system, dispersed by the optical system and measured via the sensors by the readout system.
- It is now an
“Instrument to measure intensities of light“
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Calibration
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Calibration
An “Instrument to measure intensities of light“ only by calibration becomes an analytical instrument to analyze concentrations of Elements in an sample.
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Calibration
The intensity of light related to an element is proportional to the concentration of the element in the sample.
The calibration is established by using calibration samples with known concentration of elements inside.
The analysis of unknown samples is related to the calibration with the calibration samples. The method is a relative one.
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Calibration samplesCalibration samples should have the following properties:- The composition should be similar to the unknown sample(s)- They should be homogeneous
- The concentration should be as “true“ as possible. This is the case when using CRMs (certified reference material)
Calibration
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Calibration
CRM:
The composition is of such a sample is analyzed by 5 or moreindependent laboratories
The manufacturer uses an international approved statisticalprocedure to calculate the best average and the deviationof this interlaboratory results. A certificate is part of the sample which describes all procedures used and the results.
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Calibration
With CRMs and possibly customer samples (secondary standards or RM) the instrument is calibrated.
For different elements different wavelenght are selected. Rule:
- for low concentrations a sensitive line is selected- for high concentrations a less sensitive line is used
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Calibration
Example of a calibration curve (Cu in steel) % Concentration Cu
Intensity (x 1000)X = Calibration samples
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Calibration
From measuring intensities to display the concentrations in %(weight) there are several steps of calculation.
This steps are explained next:
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Calibration
1. Intensity
2. Intensity ratio
3. IE (inter Element) Corrected intensity ratios
4. IE (inter Element) Corrected standardized intensity ratios
5. Concentration ratios
6. Concentrations
7. Typestandardized concentrations
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The intensity of a spectral line is divided by the intensity of the „matrix element“. The matrix element is the element which is 50% or more in the sample. In steel its Fe. The intensity of the matrix element is called reference intensity.
Calibration- Intensity ratio -
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Why are ratios used?The rationing compensates changings of the status of the instrument during time. This changes are caused by:- Changes of the excitation system (i.e. change in the sample composition)- Pollution by condensate in spark stand- Pollution of optical components (windows, lenses etc.)
Calibration- Intensity ratio -
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Intensity changes are compensated by calculating the ratio:
Measurement now : Measurement later :
Intensity Ni = 1000 Intensity Ni = 900----------------------------- ---------------------------Intensity Fe = 10000 Intensity Fe = 9000
The ratio is in both cases 0.1
Calibration- Intensity ratio -
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Intensity ratios :
- The intensity ratio is multiplied by a so called “typical value“ to get numbers which are looking like intensities and not like concentrations. It is just a “cosmetic“ procedure. - The typical value is usually the intensity of the reference element line running the “pure sample“, that means pure Fe in steel matrix.
Calibration- Intensity ratios -
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Example:
Int. element Cr 1000-------------------------------- X typ. Int. Fe 10000 =Int. Reference Fe 10000 1000--------- · 10000 = 1000 10000
Now the intensity has dropped 20 %» Conclusion
800 --------- · 10000 = 1000 Instrument is stabile! 8000
Calibration- Intensity ratios -
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Corrected intensity ratio :
So called additive and multiplicative corrections are done to the ratios:
- Additive interferences caused by line interference
- Multiplicative interferences caused by matrix effects
WHATS THAT??
Calibration
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Additive interference:
The line of an other than the considert element is so close that it adds a part of ist intensity to the intensity considert. By carefull selection of the lines this can be reduced but never eliminated.
WHATS THAT?
Calibration
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Example of a line overlap (additive interference):
Exit slit
Mo
Mn
On the peak maximum of Mo there is a significant interference of Mn
Calibration- Corrected intensity ratio -
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XXX
XX
X
The intensity caused by Mn must be subtracted (corrected)
from the intensity of Mo.
Calibration- Corrected intensity ratios -
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Multiplicative interference:
Interference caused by physical and chemical properties of the sample which influences the discharged plasma.
Calibration- Corrected intensity ratio -
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Corrected standardized intensity ratio:
During “standardisation“ the actual measured intensity ratios (actual values) are transformed by mathematical calculations into those measured during calibration (desired values).
Calibration
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Why standardizing?
Every spectrometer shows changing in the intensities with the time. This changes have the same reason why ratioing is neccessary:- Changes of the exitation system (i.e. change in the sample composition)- Pollution by condensate in spark stand- Pollution of optical components (windows, lenses etc.)To be able to use the original calibration curves after those changes standardizing is neccessary.
Calibration- Corrected standardized intensity ratios -
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For every calibration curve a sample with low concentration (low sample) and one with high element concentration (high sample) is selected.
This samples are measured during the calibration and the intensity ratios are stored as desired values.
Performing a standardisation later, the measured intensity ratios (actual values) are compared with the desired ones and a transformation equation is calculated.
Calibration- Corrected intensity ratio -
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Calculation: Int. HSexpected - Int. LSexpected
Factor = ------------------------------------Int. HSactual - Int. LSactual
Int. HSactual * Int. LSexpected - Int. HS expected * Int. LSactual Offset = ---------------------------------------------------------------- Int. HSactual - Int. LSactual
Calibration- Corrected intensity ratio -
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Factor and Offset are the coefficients for the transformation of actual intensities into the intensities during calibration:
Standardized corrected intensity ratios =
corrected intensity ratios * Factor + Offest
Calibration- Corrected intensity ratio -
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Concentration ratio:
- Since the calibration is done using concentration ratios instead of concentrations the first result using the calibration curve is concentration ratio. - It is calculated: % Element ---------------- · 100 % Matrix
Calibration
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Calibration
Concentration ratio:
- The concentration of the matrix element is calculates as 100% - Sum(% elements)
- To calculate the matrix concentration it is neccessary that almost all elements are analyzed by the instrument
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Calibration- Concentration -
Concentration:
After calculating the matrix concentration the software calculates each element concentration interactively for its concentration ratio.
Now the final CONCENTRATION is displayed
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Example on instruments
Q2 ION
Q4 MOBILE
Q4 TASMAN
Q8 MAGELLAN
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Automation, possible configurations.
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Future?
Inclusion Analysis / Steel Cleanliness Determination by Spark OES
Characterization of inclusions in steel byOES Pulse Discrimination Analysis (OES-PDA)
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Reference Method for Inclusion Analysis:SEM/EDS with Bruker Quantax 400 EDS
Scanning electron microscope with energy dispersive x-ray spectroscopyUniversal method: differentiation of carbides, oxides, nitrides, sulfidesLarge observation areaImaging methodHighest accuracySurface method, low penetration depth (~1µm)Costly, long measurement time (~3-10h)Highly educated operating staff
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Reference Method for Oxygen Analysis:melt extraction with G8 GALILEO
Melt extraction with carrier gas method for the determination of oxygen
Accurate analysis of total oxygenFast measurement (~80s)High analysed sample mass (~1000mg)Demanding sample preparationLimited to oxygen only
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Rapid Method for Inclusions & Oxygen:OES-PDA = MCI = Metal Cleanliness Inspection
Inclusion characterization & oxygen determination by Optical Emission Spectrometry with Pulse Discrimination Analysis
Complete elemental analysisDetermination of various oxide and sulfide inclusionsCalculation of total oxygenSimple sample preparation (grinding w/ SiC paper or milling)
Fast measurement (~5s/burn, multiple burns recommended, e.g. 5x)
User-friendly software for „normal“ OES operatorFeasibility study advisable
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Single Spark EvaluationIdentification of Coincidences
Example for single spark signals with the Q8 Magellan
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Comparison of Methods
SEM/EDS ON/(H)OES-MCI
Capital investment (approx. k€) 550 60 80
Operating costs High Medium Low
Reference method / norm compliance
Yes Partly No
Penetration depth (of sample), approx.
1-3 µm Complete 10 µm
Tested area (of sample), approx. 200 mm² Complete 7 mm² )*
PDA/MCI-Measurement time, approx.
10 h 80 s )* 5 s )*
Ease-of-use (instrument) Complex Medium Easy
Sample preparation Medium Complex Easy
Analytical performance / value High Limited Medium
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Thank you very much for your attention!
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www.bruker-elemental.com
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