Laser Induced breakdown spectroscopy in Water for elemental analysis.

1
Laser Induced breakdown spectroscopy in Water for
elemental analysis.

• Satyanarayan Ray Pitambar Mohapatra
• Project Guide Dr. R.K. Thareja

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Advantages of LIBS technique

• Can be used for rapid and remote analysis.
• Real time analysis possible.
• Complete elemental coverage can be achieved.
• The analysis spot size is small.
• Relatively low detection limit ( ppm/ppb).

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Possible application

• Detection of elements in nuclear reactors.
• Detection of elements inside deep sea.
• Space mission detection of elements in other
  planets.
• Environmental monitoring (soil contamination,
  particulates) .
• Materials analysis (metals, plastics).  
• Forensics and biomedical studies (teeth, bones
  analysis).  
• Military and safety needs (explosive particles,
  chemical and biological warfare agents e.g.
  Anthrax).  
• Art restoration/conservation (pigments,
  precious/ancient metals).  

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LIBS on Mars !

• A 300 mJ laser pulse can detect from 25m away.
• A 2 J laser pulse can detect from 100m away.
• photo credit
  Chemistry Division , Los Alamos National
  Laboratory

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Set up
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Setup specification

• Wavelength of laser radiation 355 nm
• Energy of laser radiation 18 mJ
• Focal length of Plano-convex quartz lens 10 cm
• Pulse repetition rate 10 Hz
• Gate width for time integrated spectra 2 micro
  second
• Gate width for time- resolved spectra 500 ns
• Gate delay with respect to laser pulse 300 ns

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Advantages of water based test samples

• Relatively low conc. Solution (ppm) can be
  prepared.
• Solution in water are more homogeneous than solid
  ( so spatial variation of concentration is not
  there).

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Why Na ?

• Easily available element to start with.
• To determine the concentration of Na in sea ice.
  
• Na concentration in blood and cells.

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Typical sodium lines time integrated

• Na I 589 nm
• ( 3s 2S-3p 2P0)( J 1)
• D1 line
• Na I 589.6 nm
• ( 3s 2S-3p 2P0)( J 0)
• D2 line

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Time resolved data for concentration 38 ppm
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Time resolved observation for concentration 102
ppm, gate delay 300 ns
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Time resolved data of Sodium line for
Concentration 409 ppm, gate delay 300 ns
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Calibration curve D2 line

• Detection limit 3s /m
• Detection limit observed (123 17) ppm

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Calibration curve for D1 line

• Detection limit 3s/m
• Detection limit observed (11613) ppm

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Calibration curve D2 line

• Detection limit 3s/m
• Detection limit observed (19 5) ppm

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Calibration curve for D1 line

• Detection limit 3s/m
• Detection limit observed (7.83) ppm

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Detection limit optimization

• Two types of background noise plasma continuum
  detector noise.
• Optimization
• Optimum gating time optimum position
• of detector.
• Study of temporal and spatial expansion of plasma
  in air.

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Problems to be fixed and future plans

• An actual set up should have the capability to
  distinguish among several elements.
• For that suitable wavelength of laser radiation
  to be decided.
• Suitable energy of laser radiation to be
  determined.
• Plasma parameters (plasma temperature, plasma
  density) to be determined for different
  elements.
• The LIBS method should be compared with other
  standard authentic methods.
• Salt solution of sodium and magnesium in the form
  of ice cubes to be analyzed.