Introduction to Laser Induced Breakdown Spectroscopy (LIBS) for Glass Analysis
Module 4
José R. Almirall, Erica Cahoon, Maria Perez, Ben Naes, Emily Schenk and Cleon Barnett
Department of Chemistry and Biochemistry
International Forensic Research InstituteFlorida International University, Miami FL USA
Outline
• LIBS theory and background
• LIBS setup and practice
• Glass as a model analysis matrix
• Comparison of LIBS to other elemental analysis methods in forensic science
• LIBS data analysis
LIBS Background
First reported by Maker, Terhune and Savage in 1963
• A focused laser pulse interacts with a target material to generate a practically totally ionized gas (plasma).
• The plasma then excites the substrate’s atoms and ions.
• A characteristic emission is detected.
• The emission spectrum is spectrally resolved to provide qualitative and (semi) quantitative analysis of the material.
• Direct sampling of gases, liquids and solids to determine elemental composition.
LIBS Developments
Number of publications over the last 40 years (but still less maturethan ICP and XRF as an analytical method)
Source: M. Sabsabi from Cremers and Radziemsk, 2006
Atomic Emission Spectroscopy
• Ability to detect all elements
• Simultaneous multi-element detection
• Fast and easy to operate
• No sample preparation
• Almost non-destructive
• Good sensitivity for a wide range of elements (down to 5 ppm)
• Capability of field and stand-off analyses
LIBS Overview
• Remote sensing Potential hazardous materials at long distance(80m) Aerosol identification
• Quality control Pharmaceutical Steel and alloy company
• Non destructive analysis on materials Art pieces Precious gems
• Biological and environmental safety Discrimination of bacterial species Environmental pollution in fish, plant, and paint
Plasma as an Excitation Source
ICP Plasma:
• ~ cm in length
• sustained and controlled with gas flow
• ne ~ 1 x 1015/cm3
• Temperature ~ 8000 0K
LIBS Laser Plasma:
• ~ mm in length
• created with ns laser pulse
• ~ microseconds lifetime
• ne ~ 1 x 1016/cm3
• Temperature ~ 10000 0K
* Not on same scale
Source of photo: Cremers and Radziemski 2006 8
2. www.shsu.edu/.../ JABLONSKI.html
Vibrational relaxation
Three Non-radiative Processes
1. Internal conversion
2. Intersystem crossing
3. Vibrational relaxation
Jablonski diagram
Non-radiative process
Fluorescence: S1 S0
Phosphorescence: T1 S0
GAS PHASE ATOMS, NO VIBRATIONS& ROTATIONSSHARP LINES (~ 5 pm WIDE)
HIGH SELECTIVITY
Ei
M+*
M*
M
(II) LINES, +1 ION
M+ + e-
STATE j
(I) LINES, NEUTRAL ATOM
ATOMIC SPECTRA
*Intensity of line from level j population of level j e-Ej/kT
EMISSION LINES
Laser-sample interaction time scale
100 fs laser
nanosecond laser
Russo, et al, Anal. Chem. 2001, 74, 70A-77A
Plasma temporal analysis
Source: Cremers and Radziemski 2006
RadiationRadiation
samplesample
Shock WaveShock Wave
hot, highhot, high--pressure pressure Strongly absorbing Strongly absorbing PlasmaPlasma
Laser PulseLaser Pulse
Plasma creation Plasma Evolution
14
• Continuum MiniLite Nd:YAGs Two lasers (PIV) system 2nd harmonic 532nm 22 mJ max energy per pulse 0.67 Hz Rep Rate
• New Wave Tempest 4th harmonic 266 nm 27 mJ max energy per pulse 0.67 Hz Rep Rate
• Focal length = 150 mm• Varying focus positions wrt sample
surface• Delay between laser pulses varied
from 0.0 - 10.0 µs.• Spectrometer
Mechelle 200-900nm Resolving power 5000
• Detector Andor iCCD Camera
Experimental Setup
FIU SetupAdvantages of LIBS
• Qualitative and (semi) quantitative? analysis • Almost non-destructive direct solid sampling• Minimal (or no) sample preparation• Speed, versatility, ease of operation and portability• Good detection limits (~ 5 ppm - 50 ppm)• Good discrimination power ??? • Affordability in comparison to LA-ICPMS
• Calibration for quantitative analysis• Matrix effects
Challenges of LIBS
Some Analytical Applications of LIBS
• Trace metal detection (1999)
• Trace metal accumulation in teeth (1999)
• Glass composition (2000)
• Detecting gunshot residue (2002)
• Microanalysis of tool steel (2003)
• Detection of gunshot residues on the hands of a shooter (2003)
• Analysis of energetic materials (2003)
• Hair tissue mineral analysis (2003)
• Detection of trace elements in liquids (2003)Df1-f2= F1+F2=-50+150=100 mm apart
UV
IR
45º Fused Silica Mirrors• λ, damage threshold, angle of incidence
Plano-concave lens: neg. focal length1(-50) , diverges beam
Plano-convex lens: pos. focal length2 (100), Collimates Beam
Plano-convex lens: pos. focal length2 (150mm), focuses collimated light
Plano-convex lenses: pos. focal length (75mm), collimates and focuses beam
Fiber optic cable leading to Mechelle 5000 spectrometer, 200-950 nm
Commercial LIBS Systems
AvantesFoster and Freeman
Ocean Opics
PhotonMachines NewWave Research
Avantes Spectrometer
NIST 614 (~ 2 ppm)
NIST Standard Reference Materials610 = 515 ppm Sr1831 = 112 ppm Sr
NIST 1831 Float Glass Standard1064 nm 10 laser shots1.5 µs detector delay100 µs integration time220 - 950 nm spectral range Resolution ~ 5000 over range
NIST 610 Glass Standard1064 nm 10 laser shots1.5 µs detector delay100 µs integration time[Sr] 515.5 ppm (~ 0.05%)
Sr (II) 407.77Sr (II) 421.55
NIST 610 Glass Standard266 nm 10 laser shots1.5 µs detector delay100 µs integration time[Sr] 515.5 ppm (~ 0.05%)Sr (II) 407.77
Sr (II) 421.55
NIST 1831 Float Glass Standard1064 nm 10 laser shots1.5 µs detector delay100 µs integration time[Sr] 89.1 ppm
Sr (II) 407.77
Sr (II) 421.55
NIST 1831 Float Glass Standard266 nm 10 laser shots1.5 µs detector delay100 µs integration time[Sr] 89.1 ppm
Sr (II) 407.77Sr (II) 421.55
NIST 621 Container Glass Standard266 nm 10 laser shots1.5 µs detector delay100 µs integration time[Sr] 106 ppmSr (II) 407.77
Sr (II) 421.55
XRF spectra and figures of merit
Courtesy of Scott Ryland, FDLE, Orlando, FL
Rh x-ray tube40 keV beam potential300 micron diameter monocapillary focusing collimatorLi drifted silicone EDS with beryllium windowbeam current adjusted to achieve a 35% dead time factor (approximately 760 microamps)17 microsecond time constantresolution approximately 156 eV
LIBS spectra (NIST Glass)
LIBS spectra
dual pulse
single pulse
dual pulse
single pulse
dual pulse
single pulse
LIBS & LA-ICP-MS (strontium)
Comparison of Means
0
50000
100000
150000
200000
250000
300000
350000
1 3 5 7 9
11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41
sample #
inte
n./
co
nc
.
LIBS (single)
LIBS (dual)
LA-ICP-MS (1000x)
Double pulsed LIBS:UV followed by IR reheating
[Sr] in NIST Glasses
Double Pulse enhancement for NIST 614 Glass 30 ppm certified value for K
LIBS & LA-ICP-MS (strontium)SP 1064nm
y = 319.66x - 1088.5
R2 = 0.9206
0
10000
20000
30000
40000
50000
60000
0 20 40 60 80 100 120 140
concentration (ppm)
1064nm SPLinear (1064nm SP)
XRF Intensity vs LA-ICP-MS
R2 = 0.9911
0
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100 120 140
[Sr] LA-ICP-MS Results (ppm)
(μXRF data from Ryland)
Correlation of LA-ICPMS andμXRF
LA-ICP-MS, μXRF and LIBS
150 combinations (of the possible 210) produced no Type I or Type II errors
210 ways to compare 6 element ratios between pairs
B. Naes, S. Umpierrez, S. Ryland, C. Barnett and JR Almirall;, Spectro. Acta Part B: Atomic Spectroscopy, 2008.
43
325 s delay 400 s delay
117.1 pL volume, 60.7 µm diameter per drop
Using a 1000 ppm Sr solution – 1 drop contains ~ 117pL and 117 pg of Sr
44
325 s delay
104.5 pL volume, 58.5 µm drop diameter (± 1%)
Using a 500 ppm Sr solution, 1 drop contains ~ 52.3 pg of Sr
Jetlab IV by MicroFab Technologies, TX45
50 m diameter nozzle
Target for deposition/ablation
46
~250 μm diameter, ~12 μm deep
Deposition of ~ 117 pg of Sr on an Al surface
47 48
S/N ~ 70 for ~ 100 pg depositedLoD ~ 4.3 pg Sr
Signal accumulation over 20 laser shots
Sr II 407.7 nm
49
Deposition of 1, 2, 4, 6, 8 and 12 drops of 500 ppm [Sr] on Al Microdrop printing of standards
50
215 μm spot size (20 shot accumulation)
51
0 ng
26 ng
Future of LIBS
• Move towards standardization of the technique
• Combined techniques- (Raman/LIBS, LIBS/Mirowave)
• Micro-LIBS - spatial mapping of elemental composition (3-10 μm diameter craters)
• Portable LIBS
LIBS Components
• Laser Fluence : Energy/Area (J/cm2)
• Laser λ : (Nd:YAG -1064nm, 532nm, 355nm, 266nm)• Damage threshold of optics (mirrors & lens)• Mirror (polarization, angle of incidence,coatings)• Antireflection Coatings (AR coatings on lens)• Optical Transmission of materials
BK7: 350-2100nm UV-Fused Silica: 170nm-2100nm
F1 > F2 > F3