Spark OES - Trinity College Dublin

Spark Optical Emission Spectroscopy
Analytical
Workshop 2012
Dr Heath Bagshaw – CMA, Trinity College Dublin

Why Use Spark OES Analysis?
• Quick, reliable and reproducible analysis technique
• Can analyse wide range of elements
• Usually used for metals\alloy analysis, such as :-
Steel, cast iron and high alloyed steels
Non-ferrous metals and their alloys
AI: wrought alloys, casting alloys, etc.
Cu: bronze, brass, cupronickel, etc.
Mg, Zn alloys, solders
Nitrogen in steel
P in aluminium
Ultra low carbon analysis
Elements such as Se, La, Te, etc.
• Good limit of detection for most materials - generally less then 50 ppm although 10
ppm detection limits are typical.
• Higher resolution spectrometers (using PMTs) have limits of detection of

Colours - Flame Testing
• When an element is burned it burns with a distinct colour –
Barium Strontium Potassium
• These colours are due to the emission spectrum of the element.
Analytical
Workshop 2012

Analytical
Workshop 2012
Basic Theory

• The emitted radiation\light is split using a prism or diffraction grating to produce a
spectrum.
More Basic Theory
Analytical
Workshop 2012

Basics cont
• modern equipment uses a slightly different set up:-
• A diffraction grating is used to produce the spectrum and mirrors focus the radiation
onto detectors.
Analytical
Workshop 2012

Emission Spectra
• In the case of optical emission spectroscopy the EM radiation is in the visible\optical
region of the EMS which we see as different colours depending on the
wavelength\energy of the emitted photon.
• The energy of a photon and it’s wavelength are related by the following equation:-
E = hc
Analytical
Workshop 2012
λ
where h is Planck's constant (6.626 × 10 -34 joules) and c is the
speed of light (2.998 × 10 8 m/s).

Examples of Emission Spectra
Emission spectrum of H
Emission spectrum of Fe
Analytical
Workshop 2012

The System
Sample
‘sparked’ to
produce a
‘burn’
Emitted Light
Polychromatic light
CCD measures the
light intensity at
each wavelength
Diffraction Grating,
Produces a
dispersion spectrum
Computer
Calculation of results
Comparison to Standards
Data output and storage
Analytical
Workshop 2012

The Spectrometer (Schematic)
• The diffraction grating Is like a concave mirror with lines ruled on it.
• Modern Gratings have up to 4000 rules/mm.
Entrance Slit
130 – 800 nm
Grating
• The incoming light is reflected and diffracted, producing the spectrum
Analytical
Workshop 2012

The Spectrometer (Real)
Entrance Slit
130 – 800 nm
• The CCD chips simultaneously detect all incident light and determine the intensity of
each wavelength.
Analytical
Workshop 2012

The Sample
• Generally speaking the sample is metallic, flat and freshly ground.
• The sample is clamped in place and ‘sparked’ to generate a spectrum
– this leaves ‘burn’ marks on the sample:-
‘Burn’ marks
Sample
• If the sample does not ‘burn’ correctly spurious results can be produced.
• Poor burning can be caused by poor grinding and rough\uneven surfaces.
Analytical
Workshop 2012

Analysis
• The Intensity of an emission line (colour) is proportional to concentration – allows
measurement of ‘how much’ of each element is present.
• A number of standards are run first to set up a calibration curve, these take into
account any matrix matching difficulties (i.e. overlap of elements in some materials).
Take the example of Fe
Requires six standards to correctly calibrate the instrument
for Fe analysis.
Analytical
Workshop 2012

Analysis Continued
• Once calibration is completed numerous samples can be analysed.
• The sample is simply clamped into place, ‘sparked’ and a spectrum collected.
• The spectrometer collects the intensity of light at all wavelengths and compares this
to the values for the calibration standard. This gives an accurate value of the elements
present in the sample.
• Multiple sparks are collected until concordant results are obtained within an
acceptable standard deviation.
• Further samples of the same alloy type can then be analysed.
• Different alloys require re-calibration before analysis can occur.
Analytical
Workshop 2012

System Types
• Spark Optical Emission Spectrometers come in all shapes and sizes for a multitude of
uses.
• Foundry\steel making applications – usually floor standing to analyse composition of
metals during production – quality control.
• Portable units often used in manufacturing plants to assess
metal composition.
• Portable units to analyse large immovable materials
• Hand held units to assist in scrap sorting
• The smaller the unit the less accuracy In the measurements
– so convenience over quality – still useful as analysis can be
Performed anywhere.