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OES Basics

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Informations OES

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Basics of OES Instrumentation Calibration

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Basics of OES

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Historical Overview

 17th century (1666–1672): Isaak Newton Sunlight 1. Prism Spectral colors 2. Prism white light

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Historical Overview

 Isaak Newton: Light = Particle radiation Christiaan Huygens: Light = Wave phenomenon (like sonic waves)

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Historical Review

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1887: Heinrich Hertz

Light = Small part of the electromagnetic spectrum 7 

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. Kirchhoff Existence of colors in flames = Processes in the atoms Different sort of atoms = Different colors in flames

Foundation Stone for the Spectral Chemical Analysis Elemental

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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 11 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 atom an 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 1 Å = 10 -9 = 10 -10 m m Ranges Infrared range > 800 nm...

Visible range: 400-800 nm UV-range: 200-400 nm VUV-range < 200 nm...

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Basics OES

Gamma X rays rays UV visible Infrared 0.01 nm 1 nm 100 nm 400-800 nm 1 mm Radio Spectrum 1m 1 km Elemental

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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Basics OES

Atomic lines and Ionic lines  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)

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Instrumentation

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Video Automatic system with grinding 19

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Instrumentation I

Keyboard, Mouse, Printer (PC not visible) Instrumentation Sample Clamp Start/Stop Button Spark Stand with sample

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Instrumentation II

Air Con Power Supplies Vacuum Tank Source Box Vacuum Pump Integrator Boards Spark Stand Read-out & Source Controller Argon Block Not visible: Personal Computer Keyboard, Mouse, Printer Software Package

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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 23 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 24

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Instrumentation

Exitation Source    Digital generation of any current supply curves with max. 250 A peak current Discharge 10 µs to 2 ms Max. 1000 Hz spark frequency 25

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Instrumentation

 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.

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Instrumentation

sample Entrance Slit Electrode CPM detector Exit Slit CPM detector Exit Slit Exit Slit CPM detectors

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Rowland Circle Grating Elemental

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Instrumentation OPTIC

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Instrumentation

 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)

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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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Instrumentation

 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.

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32 Grating

Instrumentation

Exitslits and CPMs Connection to readout system

HV

Direct lightpath Entrance slit

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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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Instrumentation

 Photomultiplier:  CCD Detector (Charged Coupled Device) Both detectors convert light into an electrical signal (current).

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35 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 optoelectronics 37

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Instrumentation

CPM at Bruker Elemental OES

Wavelenght 1st order 800nm-580nm 580nm-540nm Used CPM Used Filter 963 GG475 934 GG475 540nm-317nm 317nm-210nm 210nm-162nm 165nm-120nm 934 933 932 911

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Wavelenght 2nd Order Used CPM Used Filter 414nm-330nm 330nm-317nm 317nm-250nm 250nm-165nm 165nm-120nm 934 934 UG5 933 UG5 922 911 Elemental

Instrumentation

Readout  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) 39

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Instrumentation

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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

 Calibration samples Calibration 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)

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Calibration

CRM: The composition is of such a sample is analyzed by 5 or more independent laboratories The manufacturer uses an international approved statistical procedure to calculate the best average and the deviation of 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 48 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

50  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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Calibration

- Intensity ratio 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.

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Calibration

- Intensity ratio  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.)

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Calibration

- Intensity ratio  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

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Calibration

- Intensity ratios  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.

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Calibration

- Intensity ratios  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

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Calibration

 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??

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Calibration

 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?

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Calibration

- Corrected intensity ratio Example of a line overlap (

additive interference

): Mo Mn 58 Exit slit On the peak maximum of Mo there is a significant interference of Mn

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Calibration

- Corrected intensity ratios X X X X X X The intensity caused by Mn must be subtracted (corrected) from the intensity of Mo.

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Calibration

- Corrected intensity ratio  Multiplicative interference: Interference caused by physical and chemical properties of the sample which influences the discharged plasma.

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Calibration

 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).

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Calibration

- Corrected standardized intensity ratios  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.

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Calibration

- Corrected intensity ratio    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.

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Calibration

- Corrected intensity ratio  Calculation:

Int. HS expected

Factor = ------------------------------------

Int. HS actual - Int. LS - Int. LS expected actual Int. HS actual * Int. LS expected - Int. HS expected * Int. LS actual

Offset = ----------------------------------------------------------------

Int. HS actual - Int. LS actual Elemental

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Calibration

- Corrected intensity ratio  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

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Calibration

 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

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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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69 Example on instruments Q2 ION Q4 MOBILE Q4 TASMAN Q8 MAGELLAN

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70 Automation, possible configurations.

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Future?

Inclusion Analysis / Steel Cleanliness Determination by Spark OES Characterization of inclusions in steel by OES Pulse Discrimination Analysis (OES-PDA)

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Reference Method for Inclusion Analysis: SEM/EDS with Bruker Quantax 400 EDS 72

Scanning electron microscope with energy dispersive x-ray spectroscopy

Universal method: differentiation of carbides, oxides, nitrides, sulfides Large observation area Imaging method Highest accuracy Surface method, low penetration depth (~1µm) Costly, long measurement time (~3 10h) Highly educated operating staff

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73 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 oxygen Fast measurement (~80s) High analysed sample mass (~1000mg) Demanding sample preparation Limited 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 analysis Determination of various oxide and sulfide inclusions Calculation of total oxygen Simple sample preparation (grinding w/ SiC paper or milling) Fast measurement (~5s/burn, multiple burns recommended, e.g. 5x) User friendly software for „normal“ OES operator Feasibility study advisable 74

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75 Single Spark Evaluation Identification of Coincidences

Example for single spark signals with the Q8 Magellan

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Comparison of Methods Capital investment (approx. k€) Operating costs Reference method / norm compliance Penetration depth (of sample), approx.

Tested area (of sample), approx.

PDA/MCI-Measurement time, approx.

Ease-of-use (instrument) Sample preparation Analytical performance / value

SEM/EDS

550 High Yes 1-3 µm 200 mm² 10 h Complex Medium High

ON/(H)

60 Medium Partly Complete Complete 80 s )* Medium Complex Limited

OES MCI

80 Low No 10 µm 7 mm² )* 5 s )* Easy Easy Medium 76

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Thank you very much for your attention!

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www.bruker-elemental.com

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