A New Instrument for Single Particle Analysis...Hydrocarbons using Laser-Induced Breakdown Spectroscopy, Combustion and Flame. Detector Atomic Emission Spectrum of Stainless Steel

A New Instrument for Single Particle

Analysis:

The Coupling of ATOFMS and LIBSErin E. McDuffie

40x103

30

20

10

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ATOF

MS-L

IBS

Inte

nsity

800700600500400300200Wavelength (nm)

Atomic Emission

Pulsed Laser Beam

Sample

Dr. Deborah Gross’s LabCarleton College - Northfield, MN

• All research focuses on aerosol analysis– Size– Chemical composition

http://en.m.wikipedia.org/wiki/File:Carleton_College_Aerial.jpg

• Recent Projects:– Particle source study

(Milwaukee)– Experimental case study

of the indoor atmosphere– Improving

instrumentation

Aerosol Time-of-Flight

Mass Spectrometer

http://www.tsi.com/uploadedFiles/Product_Information/Literature/Spec_Sheets/3800SeriesPN1933798RevD.pdf

http://styleanderror.co.uk/2011/03/basel-nouveau-hippys/gromit/

Particle

Composition

Temporal

Trends

TSI 3800

ATOFMS

Aerodynamic

Size

How We Use ATOFMS

Courtesy of Deborah Gross, Carleton College

ParticleInlet

ParticleSizing

ParticleComposition

+ -+ -

2/ tzm µ

Inte

nsity

2/ tzm µ

Inte

nsity

Each particle, sampled in real time, generatessize and 2 mass spectra

start 0

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100300µsstop

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100300µs

TSI 3800

ATOFMSShown with

nozzle inlet.

The ATOFMS Instrument

Nd:YAG

Laser

Pressure Drop

760 Torr

10-2 Torr

10-7 Torr

Velocity is Inversely Proportional to Particle Size

Velocity is Inversely Proportional to Ion Mass

Electric Field

10-5 Torr

2

21mvKE =


ParticleInlet

ParticleSizing

ParticleComposition

+ -+ -

2/ tzm µ

Inte

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2/ tzm µ

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start 0

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ATOFMSShown with

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Advantages of ATOFMS

• Continuous Real-Time Analysis– Fast sampling rate – Little-to-no sample preparation– Sample storage or transport prior to analysis

is not required• Single Particle Analysis

– Size – Composition

• Transportable!

4000

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2000

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1000

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0

Intensity

-250 -200 -150 -100 -50 0 50 100 150 200 250m/z

1.0x106

0.8

0.6

0.4

0.2

0.0

dN/d

logD

a

6 80.1

2 4 6 81

2 4 6 810

Aerodynamic Diameter (Da)

ATOFMS Data

Mass Spectra of a Single Particle Histogram of 529,161 Particles

Pb+

NO2-

HSO4-

K+

C2-

NO3-

C3+Na+

C3-

C+

O-

Data from Milwaukee particle source study, Summer 2010Courtesy of Deborah Gross, Carleton College

How Much?

http://fax-21.blogspot.com/2011/02/gromit-award.html

•Filter Analysis/Extractions

•Particle Into Liquid Samples (PILS)

•Particulate Nitrate/Sulfate Monitors

•EC/OC Monitors

•Aethalometer

•Raman Spectroscopy

•Laser Induced Breakdown Spectroscopy (LIBS)

Quantitative Analytical Aerosol

Analysis Techniques

Laser Induced Breakdown

Spectroscopy (LIBS)LIBS uses a laser induced microplasma to excite the atomic emissions of a sample in order to determine its composition

http://libs.lanl.gov/ChemCam.html

http://energy.lbl.gov/aet/_archives/aet/laser-induced.html

Advantages:

• Fast Sampling Rate

• No Sample Preparation

• Remote Sensing Capabilities

Atomic Emission

Pulsed Laser Beam

Sample

LIBS Applications and Implementations

Hahn, D. W.; Omenetto, N. Applied Spectroscopy, 2012, 66, 347-419

Atomic Emission

Principles of Operation

1) Ablation – the laser vaporizes the surface layer of the sample and ionizes a fraction of the material

2) Plasma Generation– The ions in this gaseous material forms the plasma, which heats and expands quickly

3) Excitation – Collisional excitation promotes the electronic excitation of the remaining neutral species in the plasma

4) Emission – as the plasma cools: • Atomic Emission- excited electrons in

the neutral species return to their ground state

• Ionic Emission- free electrons in the plasma recombine with ions Ground

Excited states

Emission

Excitation

++

_+_ +

_+

_+ __

Pulsed Laser Beam

Sample

E

Conventional LIBS Instrument Design

§ Line position provides species identification

§ Line intensity provides species concentration (with calibrations)

F. Ferioli and S.G. Buckley, �Measurements of Hydrocarbons using Laser-Induced Breakdown Spectroscopy,� Combustion and Flame.

Detector

Atomic Emission Spectrum of Stainless Steel

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200 300 400 500 600 700 800 900

Wavelength (nm)

Inte

nsity O

H

Ni, Fe, Si, Mn, Cr

Si SiN

.

Pulsedlaser

Laser-inducedplasma

Atomicemissioncollection

Spectrometer

Fiberoptic

.

ParticleInlet

ParticleSizing

ParticleComposition

+ -+ -

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TSI 3800

ATOFMSShown with

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LIBS

ATOFMS + LIBS!

Creating an ATOFMS-LIBS

Stage 1:LIBS Addition Development

Stage 2:Troubleshooting...

http://nz.entertainment.yahoo.com/news/article/-/14190745/wallaces-pal-gromit-was-once-a-cat-creator-says/

Developement of a New Single-Particle Research Instrument: The Coupling of ATOFMS and LIBS

Erin McDuffie and Deborah GrossDepartment of Chemistry, Carleton College, Northfield, MN 55057

INTRODUCTION

Nd:YAG Laser

The TSI Aerosol Time-of-Flight Mass Spectrometer (3800 ATOFMS) (Figure 1) is a single-particle mass spectrometer designed to measure the aerodynamic size and composition of a polydisperse aerosol in real time. Particles are sampled through a nozzle and accelerated to a velocity dependent on their aerodynamic size. This velocity is determined by measuring the time between light pulses due to scattering as the particle crosses two orthogonal continuous diode laser beams (532 nm). The distance between the lasers is known precisely, so the time can be converted into a velocity. The velocity is then converted into an aerodynamic diameter (Da) by application of a calibration equation developed by measuring the velocity of particles of known Da. The velocity is used to track the particle as it enters the source region of the bipolar time-of-flight mass spectrometer. A pulsed Nd:YAG laser (266 nm) is fired such that the contents of the particle are desorbed and ionized. The ions are introduced into the flight tubes, and two mass spectra are obtained from each sized particle, in addition to particle size information. This process should also be inducing atomic emission, which can be captured with a LIBS instrument, provided they can be integrated.

The pysical components of a conventional LIBS instrument include: - Ablation source (laser of the required energy) - Sample - Light collection and detection systemThese components integrate well with an ATOFMS instrument because ATOFMS already has an ablation source, which allows for the addition of a detection system outside the instrument with minimal ATOFMS alterations. Since the ATOFMS parameters are fixed, key features of the LIBS addition must vary from a conventional LIBS instrument design. The following sections suggest that these differences still allow for the compatibility of LIBS with ATOFMS.

LIBS uses a laser induced microplasma to excite the atomic emission of a sample in order to determine its chemical composition. Previous single-particle analysis studies have shown that LIBS can quantitatively determine the composition of species in individual aerosol particles.

Principles of Operation1:

1) Ablation - The laser vaporizes the surface layer of the sample and ionizes a fraction of the material.

2) Plasma Generation - The ions in the gaseous material form a plasma, which heats and expands quickly.

3) Excitation - Collisional excitation promotes the electronic excitation of the remaining neutral species in the plasma.

4) Emission - As the plasma cools:- Atomic Emision - excited electrons in the neutral species return to their ground state.- Ionic Emission - free electrons in the plasma recombine with the ions. The emission wavelengths are characteristic for each element.

ACKNOWLEDGEMENTS

The understanding and analysis of health and environmental effects of atmospheric particulate matter requires measurements that can provide detailed information about particle composition. An Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) is used for the semi-quantitative analysis of the composition of individual atmospheric particles upon laser-induced desorption and ionization. Integration of the spectroscopic technique of Laser-Induced Breakdown Spectroscopy (LIBS), in which light is emitted by the elemental components of the particle upon irradiation with a laser, should increase the quantitative data provided by this instrument. Besides providing quantitative data, other advantages to LIBS as a spectroscopic technique are that it requires little to no sample preparation prior to analysis, has a fast sampling rate, and remote sensing capabilities. Due to the similarities between both spectroscopic techniques, integration of the two should be straightforward and requires only minor modifications to the ATOFMS.

References:

Ablation Environment

The required energy for particle ablation is a photon density of ~5 J/cm2 per laser pulse4. Although LIBS is often performed with a Nd:YAG laser emitting a higher pulse energy than the ATOFMS laser, the required photon density per pulse can still be met in the ATOFMS-LIBS setup. To meet this energy threshold, the ODVHU�EHDP��DW�WKH�SRLQW�RI�SDUWLFOH�DEODWLRQ��UHTXLUHV�D�EHDP�UDGLXV�RI�DW�PRVW��ȝP��7KLV�UHTXLUHG�UDGLXV�was used in the equations below to determine the focusing distance of the laser beam in order to generate the required ablation energy (beam radius) in the center of the flight tubes where the particles are sampled.

Literature has shown that single particle LIBS has sucessfully provided quantititative data in low pressure environments similar to the one found in ATOFMS2,3. The plasma generation can be aided by a gaseuos atmospheric environment but is not necessary for LIBS. The presence of an electric field in the sampling region is unlike other LIBS applications. It is possible that when the particle is ablated, the ions will be drawn into the flight tubes before they can create a plasma and emit characteristic radiation. The following calculation was done using the voltages of the ATOFMS ion source in order to determine how long ions will be availbe for LIBS sampling.

Light collection occurs at the bottom of ATOFMS, 90 degrees to the axis of the ablation laser beam. An optical fiber with a 25 degree field of view collects the light which travels to the detector where it is analyzed. In order to withstand the required pressure gradient a window and optical fiber mount were built and installed at the bottom of the ATOFMS between the two source plates (Figure 4). This swivel mount seen in the figure allows for the optical fiber to be held in place against this window while its angle of collection can be changed by up to 20 degrees. Initial spectra of stationary light sources have confirmed the dependence of spectral intensity on fiber optic collection angle.

LIBS and ATOFMS have unique timing requirments that have to be combined by syncing aspects of their electrical timing cicuits. LabView was used to write a program that incorporates the two and that allows the user to set the LIBS electronic parameters while maintaining single particle analysis (primary advantage of ATOFMS). The LIBS addition was physically incorporated using a 5V trigger pulse sent from the Nd:YAG laser while the origianl ATOFMS timing circuit was left unaltered. This pulse (Lamp Sync in Figure 6) triggers the UV-VIS VSHFWURPHWHU�WR�EHJLQ�WKH�GDWD�DFTXLVLWLRQ�SURFHVV��ȝV�EHIRUH�WKH�ODVHU�SXOVH�ablates the particle. Once triggered, the LIBS detector is programed to aquire light IRU��ȝV��ZKLFK�DOORZV�IRU�FROOHFWLRQ�RI�DQ\�SRVVLEOH�DWRPLF�HPLVVLRQ�

The funding for this project was provided by Carleton College. We thank Markus Gaelli and Gregg Lithgow at TSI for their assistance. We also thank Mark Zach for his consultation and building of the swivel mount.

1) Hahn, D. W.; Omenetto, N. Applied Spectroscopy. 2012. 64(12), 335-366. 2) Lithgow, G. A.; Robinson, A. L.; Buckley, S. G. Atmospheric Environment. 2004. 38, 3319-3328.3) Effenberger, A. J.; Scott, J. R. Sensors. 2010, 10(5), 4907-49254) Rieger, G. W.; Taschuk, M.; Tsui, Y. Y.; Fedosejevs, R. Spectrochimica Acta Part B. 2003. 58, 497-510. 851-864.

Spectrometer

LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS)

AEROSOL TIME-OF-FLIGHT MASS SPECTROMETRY (ATOFMS)

Although evidence above supports the sucessful integration of ATOFMS and LIBS, the extent to which the four operational principles of LIBS (see above) hold in an electric field and at low pressures requires the following future experiments.

Electric Field - ATOFMS-LIBS will sample while the ATOFMS voltages are turned off to allow for the ionic species to remain in the light collection region instead of traveling into the flight tubes

Low Pressures - ATOFMS-LIBS will sample while the mass spectrometry region is vented to allow for particle ablation in a gaseous environment near 1atm pressure instead of in a vaccum.

RESOLUTION OF UNCERTAINTIES

Parameter Conventional LIBS ATOFMS-LIBS

Fiber optic ��ȝP��ȝP��Distance <15mm 80mm Position fixed position window, swivel


Wavelength 266 -1064 nm 266nmEnergy 40-100mJ/pulse ~1mJ/pulse

SYNCING ATOFMS AND LIBS

Ground

Excited statesE

Excitation Emission

Atomic Emission

Pulsed Laser

Beam

Sample

Figure 2. LIBS Basic Principles

��ȝV

8ns

Ionic Emission136-140ȝV

Atomic Emission~136-190ȝV

Molecular Recombination138-240ȝV

Time = 0

Nd:YAG Laser Pulse

Data Collection

Plasma Evolution

Lamp SyncTrigger Pulse

Particle AblationTime = 136ȝV

Mass Spectra Collection~336ȝV

LIBS Data Collection~1340ȝV

S S

Not to ScaleFigure 6. ATOFMS and LIBS Timelines

Figure 4. Optical Fiber Swivel Mount

INCORPORATING A LIBS INSTRUMENT INTO ATOFMS:

VqPE *

2

2

1 mvKE

Figure 5. Example Calculations of Particle Speed for Chloride Ion

Chloride ion is one of the smaller/faster ions found in aerosols and therefore can be used to GHWHUPLQH�WKH�XSSHU�OLPLW�RI�WKH�VSHHG�RI�VDPSOHG�LRQV��FP�ȝV��DQG�WKH�PLQLPXP�WLPH�WKH\�ZLOO�EH�DYDLODEOH�GXULQJ�/,%6�VDPSOLQJ��URXJKO\��ȝV��)RU�FRPSDULVRQ��OHDG�LRQ�

�PROHFXODU�ZHLJKW��J�PRO��ZLOO�KDYH�D�VDPSOLQJ�WLPH�RI��ȝV��$V�VHHQ�LQ�)LJXUH��ERWK�species will be present during the short time atmoic emission is collected.

When the laser beam ionizes a particle, it becomes charged and finds itself in an electric field between two source plates with a potential energy based on its charge (Equation 1).

potential energy (J) = ion charge (coulombs) * voltage (volts)= 1.602x10-19C * 2318V

= 3.74x10-16 J for Cl-

This potential energy is converted into kinetic energy based on the ions mass (Equation 2).

kinetic energy (J) = 1/2 * ion mass (kg) * velocity2 (m/s) 3.74x10-16 J = 0.5(5.87x10-26kg) * v2

velocity = 112430m/s for Cl-

1)

2)


Atmospheric Gaseuos VacuumComposition (nitrogen flow)

*Pressure 760 Torr (1 atm) 1x10-7 Torr

*Electric Field None Strong

Lf W

fW*

*

SO

)*

*(1)(

2f

fR WzWzW

SO

�

Ȝ �ZDYHOHQJWK�RI�ODVHU�EHDP��QP�f = focal length (100mm)z = distance from the focal point

WL = radius the entering beamWR(z) = radius of beam at a distance of zWf = radius of beam at the focal point from the focal point

Figure 3. Laser Beam Energy Calculations

For ATOFMS-LIBS: Wf = 7ȝP��:R�]�� ȝP��]� ��PP�

This distance, beam readius, and energy are attainable with the current ATOFMS optics

Optical Fiber

Figure 1. TSI 3800 Aerosol Time-Of-Flight Mass Spectrometer (ATOFMS)

with LIBS Addition

Aerosol In

Diode-pumped Solid

State Lasers (532nm)

(Sizing Lasers)

Reflectron

(”Ion Mirror”)

Flight Tube

Ultraviolet Laser (266nm)

(Desorption/Ionization Laser)

Microchannel Plate

Ion Detectors

Ellipsoidal Mirrors

Particle

Sizing

Region

Mass

Spectrometry

Region

+Ions -Ions

Photo Multiplier

Tubes (PMT)

Particle

Sampling

Region

LIBS Data

Collection

and Analysis

RegionSpectrometer

Light Collection and DectectionGeneral Physical Components

1) Laser: Nd:YAG

2) Sample: Aerosols

3) Collection/Detection System:- Fiber: 400μm- Spectrometer: OO USB2000+- LIBS-ATOFMS Connection:

Window / Fiber Swivel Mount

http://www.oceanoptics.com/Products/usb2000.asp

LIBS Addition Development - Troubleshooting

Data Collection

• Program Requirements1) Spectrometer Control2) Single particle analysis

http://www.ni.com/labview/whatis/


Background Scans

Sync Acquisition to ATOFMS

Timing System

Tune Parameters

Front Panel Control

Save Data


LIBS-ATOFMS: Implementation

Spectrometer/Detector

Lab View Program

Window Into ATOFMS

Fiber Optic

1. Physical Components2. Data Collection/Analysis

Physical Instrument Development - Troubleshooting

Initial Results

• Functional Detection System!

Atomic Emission Spectrum of FeCl3-HNO3

Solution

-1000

4000

9000

14000

19000

24000

29000

34000

39000

200 300 400 500 600 700 800

Wavelength (nm)

Inte

nsity

Nd:YAG Laser

532nm

266nm


Where is the Signal?Comparison of Parameters

ATOFMS-LIBS

Q-Switched Nd:YAG –266nm

~1mJ/pulse

Negligible Atmospheric Composition

1x10-7 Torr

Strong

OO USB 2000+

~1 μm aerosol

Conventional LIBS

Q-Switched Nd:YAG-1064nm

40-100mJ/pulse

Gaseous Atmospheric Composition

760 Torr (1 atm)

None

High Resolution Detector

Large, solid surface

Parameters

Laser Type

Laser Pulse Energy


Ablation Pressure

Electric Field

Spectrometer

Sample Type


LIBS Under Similar Conditions

• Ambient Aerosol Analysis• Low laser energy

– ~1μJ pulses• Low pressure

– <10-6 Torr• Negligible Gaseous

Environment – reduced plasma-

surrounding interactions

Effenberger, A. J.; Scott, J. R. Sensors. 2010, 10(5), 4907-4925

Comparison of LIBS spectra of Si at atmospheric and 10-6 Torr


ATOFMS-LIBS


~1mJ/pulse


1x10-7 Torr

Strong

OO USB 2000+

~1 μm aerosol

Conventional LIBS


40-100mJ/pulse


760 Torr (1 atm)

None



Parameters

Laser Type

Laser Pulse Energy


Ablation Pressure

Electric Field

Spectrometer

Sample Type


Types of Experiments

• Laser energy/ position– Position laser beam’s

focal point to particle path• Fiber position

– Light collection angle• Detection integration time• Voltages off

– Remove electric field• Sample

– Aerosol vs solid aluminum target

Atomic Emission Spectrum of FeCl3-HNO3

Solution

-1000

4000

9000

14000

19000

24000

29000

34000

39000

200 300 400 500 600 700 800

Wavelength (nm)

Inte

nsity


Sample Change

• From aerosols to aluminum

Top-Down View of ATOFMS Flight Tubes

Laser


Results


Results


Al

N, H

ATOFMS-LIBS


~1mJ/pulse


1x10-7 Torr

Strong

OO USB 2000+

~1 μm aerosol

Conventional LIBS


40-100mJ/pulse


760 Torr (1 atm)

None



Parameters

Laser Type

Laser Pulse Energy


Ablation Pressure

Electric Field

Spectrometer

Sample Type


Remaining Uncertainties

Atomic Emission Spectrum of Stainless Steel

0

200

400

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800

1000

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1400

200 300 400 500 600 700 800 900

Wavelength (nm)In

tens

ity O

H

Ni, Fe, Si, Mn, Cr

Si SiN

Now that we have obtained signal...• Grant for new Detector• Signal Optimization and Calibration• Write a data analysis program

A Work In Progress:

The Future of ATOFMS-LIBS

New Instrument!!

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Intensity

-250 -200 -150 -100 -50 0 50 100 150 200 250m/z

Mass Spectrum of a Single Particle

!

Acknowledgements

• Deborah Gross• Carleton College Faculty

– Including Steve Drew and Mark Zach• Markus Gälli and Gregg Lithgow at TSI• Carleton College Department of Chemistry

Documents

A New Instrument for Single Particle Analysis...Hydrocarbons using Laser-Induced Breakdown Spectroscopy, Combustion and Flame. Detector Atomic Emission Spectrum of Stainless Steel