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