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Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)
Sample IntroductionSystem
Atom Excitation Ion Generation Source - Plasma
Mass to Charge (m/z)detector
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LA-ICP-MS- the concept
Laser Energy
Solid sample
Solid vaporization
Dissociation
Atomization
Ionization/Excitation of elements
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UV laser (226 nm)
Sample
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Laser
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Ar gas
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Ar gas
Vaporized sample aerosol
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Ar gas
Transport tube to ICP
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Ar gas
Sample
Vaporized sample aerosol
Transport tube to ICP
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Ar gas
Sample
Vaporized sample aerosol
Transport tube to ICP
ICP
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Ar gas
Sample
Vaporized sample aerosol
Transport tube to ICP
Sample crater
ICP
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Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)
Sample IntroductionSystem
Atom Excitation Ion Generation Source - Plasma
Mass to Charge (m/z)detector
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ICP-MS
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Plasma?• Partially ionized gas
• Aro, Ar+, and e-
• Temp: 10,000 K • Three concentric quartz tube• Argon plasmas are most common
• Ar flow rates : 10-15 L/min; • Auxiliary < 2 L/min
• Analytical observation region (on top)• Water cooled rf (radio frequency) load coil
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Fate of the Sample AerosolDesolvation H2O (l) -> H2O (g)
Vaporization MXs -> MXl -> MXg
Atomization MXg Mg + Xg
Excitation Mg-> Mg*
Ionization Mg-> Mgn+ + ne-
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Ions • 54 elements > 90% are ionized• Metalloids As, P, Se
• Plasma ions: Ar -> Ar+ + e-
• Water -> H+, OH-, O-
• Analyte Ions -> M -> M+ + e-
• Doubly charged ions (M2+)• Depends on the second ionization energy• 10% of the total analyte ions• Possible suspects: Ba2+, rare earth elements
(REE)
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Ion ExtractionM +
CollectFocus
Transmit to the mass analyzerDetector
(channeltron electron multiplier, faraday cup)
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ICP-MS interface
• Ambient pressure to low pressure (vacuum)• Two stage interface
• Sampling cone (pressure drops to 2.5 mbar)• Skimmer cone (pressure drops to c.a. 10-4 mbar)
• A Slide valve for close the interface hole when the instrument is not in use
Plasma -Ion Source
Mass Analyzer
MSICPSampler
Skimmer
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Plasma → Sampler → Skimmer → MS
Sampler:Sampler (r=1.0 mm) water cooled coneIons are sampled from the central region of the plasma
Formation of oxidesCondensation of solids
‘supersonic’ jet’ expansionP=2.5 torr
P p
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Interface
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Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)
Sample IntroductionSystem
Atom Excitation Ion Generation Source - Plasma
Mass to Charge (m/z)detector
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Quadrupole mass analyzer
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Mass Analyzers• Quadrupole mass analyzer (m/z range 1-300)
• Magnetic sector mass analyzer (for high precision measurements)
• Time of the Flight (TOF) mass detectors
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Quadrupole mass analyzers• Rapid scanning
• Mass to mass jump (peak hop)• Takes only few μs• Real-time scanning ability• Thus, great for scanning of
chromatographic and laser profiles
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Isotopic abundances
• 40Ca 99.600% 204Pb 1.4%• 42Ca 0.647% 206Pb 24.1%• 43Ca 0.135% 207Pb 22.1%• 44Ca 2.086% 208Pb 52.4%• 46Ca 0.004%• 48Ca 0.187%
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Mass to Charge ratio (m/z) measurements• mass (m)/charge(z)
• For :- 48Ca Ca+ + 1e-
• m/z = 48/1 = 48
• Doubly charged ions:• 134Ba2+ = 134/2 =67
Interferes with 67Zn+
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Peak-hopping approachMeasurement of 54Fe and 56Fe
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ICP-MS Multielement Measurement Routine
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Potential interferencesInterferences on
Isobaric 40Ar+ 40Ca+
Polyatomic 40Ar16O+ 56Fe+
40Ar35Cl+ 75As+
Background spectrum 38Ar14N+ 52Cr+
40Ar40Ar+ 80Se+
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Types of Analysis
Bulk analysisSurface analysisChemical speciation Size fractionationIsotopic information
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Analytical Information
• Quantitative Analysis with low detection limits• Multielement (M1, M2, M3 ….) standards (i.e., 100, 10, 1, 0.1 ppb)• Linear calibration curves• Very low detection limits (ppt)
• Isotopic abundance ratio information
• Isotope dilution analysis (high precision measurements)
I/Iis
Analyte Conc. (ug/g)
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Lead isotopesIsotope Natural Abundance
204Pb 1.4% (primordial)206Pb 24.1% (non-radiogenic)207Pb 22.1% (non-radiogenic)208Pb 52.4%(non-radiogenic)
All are stable isotopes
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Radiogenic lead isotopes
232Th ----- 208Pb(6He + 4β) t ½ = 14 x 109 y
235U ----- 207Pb(7He + 4β) t ½ = 0.7 x 109 y
238U ----- 206Pb(8He + 6β) t ½ = 4.5 x 109 y
Due to the radiogenic origin of these lead isotopes, lead does not have a fixed isotopic abundance in the nature
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Lead isotope signatures
208Pb/206Pb 1.95-2.15207Pb/206Pb 0.78-0.86204Pb/206Pb 0.05-0.06
232Th/238U 232Th/238U232Th/238U
∴ 208Pb/206Pb
∴ 208Pb/206Pb ∴ 208Pb/206Pb
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Hair samples were mounted on a sticky glue tapes Laser ablation mode – single spot method, Nd(YAG)- 266 nm Laser Energy: 0.85 Average hole size - 48 ± 5 μmAblation depth – 16 μmHair samples were analyzed for
64Zn, 208Pb, 75As, 12C and 32S
Ion intensity (cps) vs. Time (s) signals were collected
LALA--ICPICP--MS AnalysisMS Analysis