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Overview of AMS Instrument and Working Principles
Qi ZhangDepartment of Environmental Toxicology
University of California at Davis
Aerodyne/Nanjing University Chinese AMS/ACSM Clinic
Nanjing University, ChinaApril 20 -22, 2018
1
15 (10 AMS,5 ACSM)
17 (3 AMS,14 ACSM)
5 (2 AMS,3 ACSM)
20 (9 AMS,11 ACSM)
Prepared by Penglin Ye
AMS/ACSM in China
IonDetector
DataProcessor
Mass Spectrum
Ion Source
MassAnalyzer
Sample Inlet
How Does Mass Spectrometry Work?
Building blocks of a mass spectrometer
Display MS
High Vacuum3
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio (m/z) and abundance of gas-phase ions generated from molecules.
IonDetector
DataProcessor
Mass Spectrum
Ion Source
MassAnalyzer
Sample Inlet
How Does Aerosol Mass Spectrometry Work?
High Vacuum4
AerosolSample
• Aerosol sampling inlet, P-ToF chamber, Vaporizer1. Aerosol sampling2. Particle sizing (AMS)3. Particle vaporization
Conceptual Schematic of an AMSAerosol Interface
AerosolInlet
ParticleSizing Vaporization
Mass Spectrometry
Ionization MassAnalysis
AerodynamicLens
Particle-ToFChem. Detect.
Impact on heatedSurface
(~ 600 oC)
e- Ionization(EI)
5
Quadrupole /ToF
• Analysis of particle ensemble• Detect non-refractory components
(evaporate rapidly at ~ 600 oC & vacuum)
critical orifice
nozzle
Orifices
Aerosol Inlet: Aerodynamic Lens
6
• Form particle beam• Concentrate aerosols
from gas-phase–by 107 vs. gas–Reduce gas-phase
interference• Particle transmission
efficiency: –PM1 lens:100% ~ 60 –
600 nm–PM2.5 lens
• Impart size-dependent velocity– To measure size by
particle time-of-flight
m d3
Fdrag d2 v
Finertia = m a a d-1
Fdrag
v v: relative velocity between the gas and the particle
Aerodynamic Forces on a Particle
Particle Sizing: Size-Dependent VelocityPressure difference b/w lens & sizing chamber Fdrag
size-dependent velocity
To DetectorAerodynamic Lens
Nozzle
Inertia Drag
2.4 Torr 10-3 Torr exit
Drag is also shape-dependent particle
morphology
DeCarlo P. et al. AS&T, 38, 1186-1205, 2004
Free-Molecular Regime
7
Jayne, J.T., Aerosol Sci. Technol., 33, 49-70, 2000.
lba
lg
p
cp v
DDvv
tLv
)/(1 *
Particle velocity
Particle diameter
Particle Sizing: Calibration
Empirical Power Law
• Analyze particles of known Da
• Determine vp for each size
• Plot & fit the data
8
Ensemble Composition
“Beam open”
Particle Beam Vaporizer
(~600oC)
ionization/detection
Determination of vp: Chopper + Chem. Detec.
Size Distribution
1500
1000
500
0
Ion
Sig
nal
8x10-36420Time of Flight (s)
Size distribution of m/z’sMass weighted size distribution
Low duty cycle signal cut by 25!
“Beam chopped”
Particle Beam
100
101
102
103
104
105
106
107
Ion
Rat
e (H
z)
28024020016012080400m/z (Daltons)
No size informationMuch higher S/N
Vaporizer(~600oC)
ionization/detection
particle
Ion
sign
al
9
AMS Detection Process (Vaporization + ionization)
Vaporizer
e-
Electron EmittingFilament
R+
Positive Ion Mass Spectrometry
Chemical Composition
FlashVaporization of
Non-Refractory (NR)components
600 CParticle
Time-Of-Flight
Particle Velocity
AerodynamicDiameter
Focused Particle Beam
Electron Impact Ionization
Universal, quantitative, and sensitive chemical analysisVaporization and analysis of most aerosol chemical constituents
- with primary exception of crustal oxides and elemental carbon. 10
Canagaratna, M. et al. Mass Spectrometry Reviews, 26, 185-222, 2007
• Hot filament (Tungsten or Rhenium) gives off electrons• e- accelerated by a potential difference• electron energy = 70 eV (NIST database, reference MS)• Interact with the gaseous molecules in their path• Hard ionization method extensive molecular
fragmentation
Electron Impact Ionization (EI)
molecule
e
e
e 70
55
0.1
4.9
frag1 frag2++
molecule
e
Fragmentation
11
Ionization Efficiency
present moleculesformed ions
IE
• Reproducible • Quantitative
• Nonselective ionization• Extensive fragmentation
Mass Analyzers: Analysis of Ions
• In the mass analyzer, gas-phase ions are subjected to a known electric (or magnetic) field.
• Electric (or magnetic) forces sort ions according to their m/z ( mass spectrum)
• Types used in AMS– Quadrupoles– Time-of-flight (TOF)
• m/z range, mass resolution
12
•Quadrupole consists of four parallel rods
•Typical length:10’s cm
•Precise dimensions and spacing
•Rods connected diagonally in pairs
• Voltages (DC + AC) applied to rods define time-varying fields between rods and determine the m/z that is transmitted. (Mass Filter)
• One m/z at a time, unit mass resolution (UMR)• Simple, rugged, lightweight
Quadrupole Mass Analyzers
13
Detector
V
Source, S Drift Region, D
E = V/S E = 0
mqEsD
vDt
mqEsv
mvqEs
qEsqVU
aDD
aD
Da
aa
2
221 2
Ions accelerated by strong field, E, within short source region, S.
Drift times recorded across long, field-free drift region, D.
vD depends on starting position of ion –ideally all ions start from same plane.
Drawing adapted from p20 of Cotter reference:
a
Cotter, “Time-of-flight Mass Spectrometery: Instrumentation and Applications in Biological Research,” ACS, 1997.
Time-of-Flight Mass Analyzers
14
m/z tD2
Ion detectors: To collect and convert ions into an electrical signal, which can be easily measured
Types of Ion Detectors• Electron multiplier• Micro-channel plate (array transducer)
Mass Spectrometry Detectors
• Ions impact the wall starts a cascade of e-
• e- propagates through the channel Very large amplification!
15http://www.chm.bris.ac.uk/ms/theory/detection.html
e-
High Resolution Time‐of‐Flight AMS (HR‐ToF‐AMS)
16Jayne et al., AST, 2000; DeCarlo et al., Anal. Chem. 2006
AMS Schematic
MS Signatures for Aerosol Species Identificationcolor coded to match spectra
Water H2O H2O+ , HO+ , O+ 18, 17, 16Ammonium NH3 NH3
+, NH2+, NH+ 17, 16, 15
Nitrate HNO3 HNO3+, NO2
+, NO+ 63, 46, 30
Sulfate H2SO4 H2SO4+, HSO3
+, SO3+ 98, 81, 80SO2
+, SO+ 64, 48Organic CnHmOy H2O+, CO+, CO2
+ 18, 28, 44(Oxygenated) C2H3O+, HCO2
+, CxHyOZ+ 43, 45, ...
Organic CnHm CxHy+ 27,29,41,43,55,57,69,71...
(hydrocarbon)
Group Molecule/Species Ion Fragments Mass Fragments
e-
e-
e-
e-
e-
e-
Standard electron impact ionization @ 70 eVEasy to quantify: ca. NIST MS libraryEasy to separate inorganic and organic componentsSpeciation of organic composition is challenging
17Canagaratna, M. et al. Mass Spectrometry Reviews, 26, 185-222, 2007
Principle of EI Mass Spectrometry and Quantification
Mass Loading A (MWA/IEA) Ion Signalai
EI Ionization: A + e- A+ ai+
m/z
msmix = ci ∙ msimsi – mass spectrum of sample ici – concentration of sample i
2 ∙ msa + 2 ∙ msb + 1 ∙ msc
ca = 2cb = 2cc = 1
Mass Loading A (MWA/IEA) Ion Signalai
EI Ionization: A + e- A+ ai+
Principle of EI Mass Spectrometry and Quantification
1st
• Fragmentation pattern of inorganic species (e.g., SO4
2-, NO3-, water, NH4
+, Cl+) & gas molecules (e.g., N2, O2, CO2, H2O)
• Isotopic ratios of elements
Continuous mass spectrum
Stick mass spectrum(UMR or HR)
Aerosol Sampling
AMS/ACSM
Size resolved MS size distributions
Ensemble MS
MS of Organics
-MS of Air
MS of Sulfate
MS of Nitrate
MS of Ammonium
MS of Chloride
MS of Water
An ensemble AMS/ACSM mass spectrum is the linear superposition of the mass spectra of individual components.
Jayne et al., AST, 2000Jimenez et al., JGR, 2003 Allan et al., J. Aero. Sci., 2004.
AMS Spectral Analysis
1st
• Fragmentation pattern of inorganic species (e.g., SO4
2-, NO3-, water, NH4
+, Cl+) & gas molecules (e.g., N2, O2, CO2, H2O)
• Isotopic ratios of elements
Continuous mass spectrum
Stick mass spectrum(unit m/z resolution)
Aerosol Sampling
Ensemble MS
MS of Organics
-MS of Air
MS of Sulfate
MS of Nitrate
MS of Ammonium
MS of Chloride
MS of Water
The concentration of a species in question is calculated by summing signals in its partial MS
E.g., Corg (g m-3) = m/ziorg
Jayne et al., AST, 2000Jimenez et al., JGR, 2003 Allan et al., J. Aero. Sci., 2004.
An ensemble AMS/ACSM mass spectrum is the linear superposition of the mass spectra of individual components.
AMS/ACSM
Size resolved MS size distributions
AMS Schematic and Data
• Real‐time measurement (sec – min resolution )• Non‐refractory submicron PM (NR‐PM1 )• NR species: evaporate rapidly at ~ 600 oC and vacuum (10‐8 torr)
Jayne et al., AST, 2000; DeCarlo et al., Anal. Chem. 2006
2. Size‐resolved composition
1. Quantitative composition
3. 0
2. 5
2. 0
1. 5
1. 0
0. 5
0. 0
Nitr
ate
Equi
vale
nt M
ass
Con
cent
ratio
n (µ
g m
-3)
141201 0080604 020m /z (D alt ons )
Am m on ium 4 .8 ug/m 3Nit ra te 5 .8Su lpha te 9 .4Organ ics 13.4Ch loride 0.15
M ex ic o C i ty 2/200 2
SO+SO2
+
S+
SO3+
HSO3+
H2SO4+
43 44
57
3. Elemental comp. (CnHmNpOzSw)
m/z 43
High Resolution Time‐of‐Flight AMS (HR‐ToF‐AMS)
C2H3O+
CHNO+C2H5N+
C3H7+CH3N2
+
~ 600 oC
Transmission: 30 ~ 1500 nm
22
(mass weighted)
Important Considerations for AMS Mass Concentration Quantification
• Ionization efficiency and relative ionization efficiencies (Qi Chen et al.)
• Collection efficiency (Weiwei Hu et al.)• Aerodynamic Lens: PM1 vs. PM2.5
• Vaporizer: Standard vs. Capture• Dependence on particle phase state…
• Sensitivity• Detection limit: 3 × σ of 1-min particle-free data
• Signal intensity and noises• IE/AB ratio• Data analysis issues: resolution, m/z accuracy, isobaric ions
(frag table), peak shape …
ReferencesAllan, J.D., Delia, A.E., Coe, H., Bower, K.N., Alfarra, M.R., Jimenez, J.L., Middlebrook, A.M., Drewnick, F., Onasch, T.B., Canagaratna, M.R., Jayne, J.T., Worsnop, D.R., 2004. A generalised method for the extraction of chemically resolved mass spectra from Aerodyne aerosol mass spectrometer data. Journal of Aerosol Science 35, 909-922
Canagaratna, M., Jayne, J., Jimenez, J.L., Allan, J.A., Alfarra, R., Zhang, Q., Onasch, T., Drewnick, F., Coe, H., Middlebrook, A., Delia, A., Williams, L., Trimborn, A., Northway, M., DeCarlo, P., Kolb, C., Davidovits, P., Worsnop, D., 2007. Chemical and Microphysical Characterization of Ambient Aerosols with the Aerodyne Aerosol Mass Spectrometer. Mass Spectrometry Reviews 26, 185-222, DOI:110.1002/mas.20115.
DeCarlo, P.F., Kimmel, J.R., Trimborn, A., Jayne, J., Aiken, A.C., Gonin, M., Fuhrer, K., Horvath, T., Worsnop, D.R., Jimenez, J.L., 2006. A Field-Deployable High-Resolution Time-of-Flight Aerosol Mass Spectrometer. Analytical Chemistry.
DeCarlo, P., Slowik, J.G., Worsnop, D.R., Davidovits, P., Jimenez, J.L., 2004. Particle morphology and density characterization by combined mobility and aerodynamic diameter measurements. Part 1: Theory. Aerosol Science & Technology 38, 1185-1205.
Jayne, J.T., Leard, D.C., Zhang, X., Davidovits, P., Smith, K.A., Kolb, C.E., Worsnop, D.R., 2000. Development of an aerosol mass spectrometer for size and composition analysis of submicron particles.Aerosol Science and Technology 33, 49-70.
Jimenez, J.L., Jayne, J.T., Shi, Q., Kolb, C.E., Worsnop, D.R., Yourshaw, I., Seinfeld, J.H., Flagan, R.C., Zhang, X., Smith, K.A., Morris, J.W., Davidovits, P., 2003. Ambient aerosol sampling with an Aerosol Mass Spectrometer. J. Geophys. Res. 108, 13.