Transcript Laser Induced breakdown spectroscopy in Water for

Laser Induced breakdown
spectroscopy in Water for
elemental analysis.
Satyanarayan Ray Pitambar
Mohapatra
Project Guide: Dr. R.K. Thareja
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).
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).
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
Set up
Setup specification
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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
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).
Why Na ?
• Easily available element to start with.
• To determine the concentration of Na in sea
ice.
• Na concentration in blood and cells.
Typical sodium lines time
integrated
• Na I 589 nm
( 3s 2S-3p 2P0)( J = 1)
D1 line
6000
D2
5000
Intensity --->
4000
D1
3000
Sodium lines
2000
1000
0
480
500
520
540
560
580
600
Pixel ( wavelength) --->
620
640
29 Sept. 2003
• Na I 589.6 nm
( 3s 2S-3p 2P0)( J = 0)
D2 line
Time resolved data for concentration = 38
ppm
Time resolved observation for concentration =
102 ppm, gate delay = 300 ns
Time resolved data of Sodium line for
Concentration = 409 ppm, gate delay = 300 ns
Calibration curve D2 line
• Detection limit = 3σ /m
• Detection limit observed
= (123 + 17) ppm
4000
Intensity (as number of counts) --->
3500
Resolution limit = 3/m
= 123 ppm
3000
2500
2000
1500
1000
D2 line of Na
500
0
0
200
400
Conc. in ppm --->
600
800
29 Sept. 2003
Calibration curve for D1 line
• Detection limit = 3σ/m
6000
Intensity (as number of counts) --->
5000
4000
• Detection limit observed
= (116+13) ppm
limit of resolution = 3/B
=116
3000
2000
1000
D1 line of Na
0
0
200
400
600
800
Conc. in ppm --->
29 Sept. 2003
Calibration curve D2 line
• Detection limit =
3σ/m
2200
Intensity (as number of counts)
• Detection limit
observed = (19+
5) ppm
2400
2000
1800
1600
D2 line of Na
1400
1200
0
10
20
30
40
50
60
Conc. in ppm
31 October, 2003
Calibration curve for D1 line
• Detection limit = 3σ/m
3200
• Detection limit
observed = (7.8+3)
ppm
Intensity ( as number of counts)
3000
2800
2600
2400
D1 line of Na
2200
2000
0
10
20
30
40
50
60
Conc. in ppm
31 October, 2003
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.
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.