A Combination of Icp - Mass Spectrometry and Synchrontron X ...

A Combination of Icp - Mass Spectrometry and Synchrontron X ...

ISOTOPIC ANALYSIS FOR BEGINNERS Frank Vanhaecke Ghent University, Belgium THE ISOTOPIC COMPOSITION OF THE ELEMENTS ISOTOPES ? Isotopes of an element M: same atomic number A Same number of protons in their nuclei Same number of electrons in their shells Identical chemical behaviour First approximation statement will be refined later Different mass number Z Different number of neutrons in their nuclei Different masses Mono-isotopic elements? 9Be, 19F, 23Na, 27Al, 31P, 45Sc, 55Mn, 59Co, 75As, 89Y, 93Nb, 103Rh, 127I, 133Cs, 141 Pr, 159Tb, 165Ho, 169Tm, 197Au, 209Bi, 231Pa, 232Th Other elements?

2 10 isotopes Relative abundances define fraction of element M as nuclide nM THE ISOTOPIC COMPOSITION OF THE ELEMENTS First approximation: all elements show an isotopic composition that is stable in nature Why ? Thorough mixing during formation of our solar system (4.6 . 109 years BP) The solar system was formed approximately 4.5 billion years ago. The material making up the solar system all came from a single, mostly homogeneous cloud of material (solar nebula). The matter rotated in a flattened plane, splayed out in a disk due to the angular momentum. With time, material not falling to the central sun, would either be thrown out of the system or begin to collect and build up planetesimals. At safe relative distances, planetesimals built up to form the planets. VARIATIONS IN THE ISOTOPIC COMPOSITION OF THE ELEMENTS 1. Decay of naturally occurring, long-lived radionuclides 2. Natural fractionation effects

3. Man-made variations 4. Interaction of cosmic rays with terrestrial matter 5. Variations observed in extra-terrestrial materials VARIATIONS IN ISOTOPIC COMPOSITION DECAY OF NATURALLY OCCURRING, LONG-LIVED RADIONUCLIDES Variations in Sr isotopic composition due to: 87 Rb 87 Sr 87Rb = naturally occurring, long-lived radionuclide T1/2 = 48.8 x 109 y Isotopic composition of Rb has changed through time Isotopic composition of Rb presently equal for all terrestrial materials Isotopic composition of Sr: variable! E.g., rocks: dependent on elemental Rb/Sr ratio + age Sr isotope

Natural range of relative isotopic abundance 0.55 0.58 % 9.75 9.99 % 6.94 7.14 % 82.29 82.75 % 84 Sr 86 Sr 87 Sr 88 Sr IUPAC, 1997 VARIATIONS IN ISOTOPIC COMPOSITION DECAY OF NATURALLY OCCURRING, LONG-LIVED RADIONUCLIDES 238U 206Pb 235U 207Pb 232Th 208Pb 204Pb: not radiogenic

B. Bourdon et al, Rev. Miner. Geochem, 52, 1-19, 2003. VARIATIONS IN ISOTOPIC COMPOSITION DECAY OF NATURALLY OCCURRING, LONG-LIVED RADIONUCLIDES Variations in the isotopic composition of Pb 238 U 206Pb; 238U: T1/2 = 4.5 x 109 y 235 U 207Pb; 235U: T1/2 = 7.1 x 108 y 232 Th 208Pb; 232Th: T1/2 = 1.4 x 1010 y

204 Pb = not radiogenic Consequences ? Isotopic comp. Pb in the presence of U and/or Th changes as f(time) Extremely slowly, cf. T1/2 Isotopic comp. Pb in rocks, dependent on Pb/U and Pb/Th elemental ratios Time during which elements have spent together Isotopic comp. Pb varies as a f(place), f(ore deposit), Pb isotope Natural range of relative isotopic abundance 204 Pb 1.04 1.65 % 206 Pb 20.84 27.48 % 207 Pb 17.62 23.65 % 208 Pb

51.28 56.21 % IUPAC, 1997 VARIATIONS IN ISOTOPIC COMPOSITION NATURAL ISOTOPE FRACTIONATION EFFECTS Isotope fractionation? Due to their relative difference in mass, different isotopes of the same element may take part with a (slightly !!) different efficiency in physical processes or in (bio)chemical reactions. Both differences in reaction rate (kinetics) and in equilibrium state (thermodynamics) have been described. THERMODYNAMIC ISOTOPE FRACTIONATION EFFECT DISSOCIATION OF A DIATOMIC MOLECULE E 1 h k E n 2 2 D0(L) D0(H)

1 1 1 m1 m2 E0(L) E0(H) r F. Vanhaecke et al, JAAS, 24, 863-886, 2009. KINETIC ISOTOPE FRACTIONATION EFFECT CHEMICAL REACTION ROLE OF ACTIVATION ENERGY h(L)* h(H)* E(H)* E(L)* Activated complex

E(L)* h(L) < E(H)* h(H) Reactant Unidirectional reaction Reaction coordinate F. Vanhaecke et al, JAAS, 24, 863-886, 2009. VARIATIONS IN ISOTOPIC COMPOSITION NATURAL ISOTOPE FRACTIONATION EFFECTS Extent of isotope fractionation? ~ Relative difference between the masses of the isotopes More pronounced for light isotopes But, discovered for more and more elements owing to higher precision in MS ~ Extent to which element takes part in processes Physical processes Evaporation, condensation Diffusion

(Bio)chemical reactions Also mass-independent isotope fractionation (rare) Difference in size between nuclei of isotopes Not always linear relation with mass Hyperfine coupling between nuclear spin & electron cloud VARIATIONS IN ISOTOPIC COMPOSITION NATURAL FRACTIONATION EFFECTS Very small effects Special notation introduced 18 O O 16 16 O sample O s tan dard 18 0 O 1,000 18 00 O

16 O s tan dard 18 18 O O 16 16 O sample O s tan dard 18 O 10,000 18 O 16 O s tan dard 18

VARIATIONS IN ISOTOPIC COMPOSITION NATURAL FRACTIONATION EFFECTS VARIATIONS IN ISOTOPIC COMPOSITION NATURAL FRACTIONATION EFFECTS Factor 2 relative difference between isotope masses 10% relative difference between isotope masses 6% relative difference between isotope masses ? Difference too small for measurable isotope fractionation ? VARIATIONS IN ISOTOPIC COMPOSITION NATURAL FRACTIONATION EFFECTS ? Difference too small for measurable isotope fractionation ? No

! von Blanckenburg et al. Fractionation reported for increasing number of (heavier) elements: improved MS precision VARIATIONS IN ISOTOPIC COMPOSITION MAN-MADE VARIATIONS mined uranium 0.715% 235 238 U and 99.28% U isotopic enrichment waste = depleted U (DU) depleted in 235

U very high density ! ammunition & projectiles penetrating armored steel fission reactor 235 fuel enriched in U counterweights in airplanes VARIATIONS IN ISOTOPIC COMPOSITION INTERACTION OF COSMIC RAYS WITH TERRESTRIAL MATTER Formation of C in the atmosphere Cosmic rays

Spalliation Production of neutron 14 14 14 N+n 14 C+p C

Radionuclide T1/2 = 5730 y Production & decay in dynamic equilibrium Constant abundance of 14 C, next to 12 C& Also other cosmogenic nuclides formed

Stable nuclides & radionuclides Extremely low concentrations In the atmosphere On the earths surface (to a lesser extent) 13 C VARIATIONS IN ISOTOPIC COMPOSITION VARIATIONS OBSERVED IN EXTRA-TERRESTRIAL MATERIALS In extraterrestrial materials, some elements show an isotopic composition not known in terrestrial materials

Extraterrestrial materials ? 107 107 Many iron meteorites display an enrichment in Ag unseen in any terrestrial silver. It is now widely accepted that the Ag enrichment is a result of the decay of the now extinct 107 6 radionuclide Pd (T1/2 = 6.5 x 10 y). Since Pd is more siderophile than Ag, core formation results in high Pd/Ag elemental ratios, as displayed in iron meteorites (these meteorites are often considered a good model for the planetesimals). Terrestrial material that is accessible on the other hand (the silicate fraction) is characterized by much lower 107 109 107 109 Pd/Ag elemental ratios. Therefore, in all terrestrial material, the Ag/ Ag isotope ratio is (very close to) 1.081. In some iron meteorites however, the Ag/ Ag isotope ratio can substantially deviate from this value (values up to 9 has been reported!). Iron meteorite (5% of meteorites)

Hoba meteorite, Namibia (50 ton) HOW TO MEASURE ISOTOPE RATIOS SINGLE-COLLECTOR ICPMS INSTRUMENTS IMPORTANCE OF ISOTOPE RATIO PRECISION Isotope ratio ? Isotope ratio 2 different populations conclusions! WHAT CAN WE EXPECT IN TERMS OF ISOTOPE RATIO PRECISION ? Ultimate limit set by counting statistics Poisson counting statistics Valid if variation in arrival of ions @ detector = statistically governed Then st. dev. (N) = SQRT(N) N = total # counts (not count rate!)

RSD %= [1/SQRTN]. 100% Ultimate limit? Importance of acquiring a high number of counts Sufficiently high signal intensities Sufficiently long measurement times TRADITIONAL QUADRUPOLE-BASED ICPMS HOW TO GET THE BEST ISOTOPE RATIO PRECISION? TRADITIONAL QUADRUPOLE-BASED ICPMS Optimum conditions? Sufficiently high signal intensities Cf. detector dead time Sufficiently long measurement time Isotope ratio close to 1 Problem? ICP = noisy source

Warning Do not compare apples & pears St. dev (mean) = st. dev. / SQRT(N) HOW TO GET THE BEST ISOTOPE RATIO PRECISION? TRADITIONAL QUADRUPOLE-BASED ICPMS pneumatic nebulization 87 86 Sr/ Sr laser ablation sufficiently high total acquisition time cf. Poisson counting statistics F. Vanhaecke et al, JAAS, 14, 1691-1696, 1999. M. Resano et al, JAAS, 23, 1182-1191, 2008. HOW TO GET THE BEST ISOTOPE RATIO PRECISION? TRADITIONAL QUADRUPOLE-BASED ICPMS signal intensity Isotope ratio 1.2 390

1 370 350 0.8 330 0.6 310 0.4 290 isotope 1 isotope 2 0.2 270 250 0 1 2

3 4 5 6 Time (arbitrary units) 7 8 9 10 HOW TO GET THE BEST ISOTOPE RATIO PRECISION? TRADITIONAL QUADRUPOLE-BASED ICPMS signal intensity Isotope ratio 1.2

390 1 370 350 0.8 330 0.6 310 0.4 290 isotope 1 isotope 2 0.2 270 250 0 1

2 3 4 5 6 Time (arbitrary units) 7 8 9 10 HOW TO GET THE BEST ISOTOPE RATIO PRECISION? TRADITIONAL QUADRUPOLE-BASED ICPMS Residence time / acquisition point Sufficiently low

Too low values? Large fraction of time lost Settling time laser ablation M. Resano et al, JAAS, 23, 1182-1191, 2008. HOW TO GET THE BEST ISOTOPE RATIO PRECISION? TRADITIONAL QUADRUPOLE-BASED ICPMS An example of data acquisition conditions: Scanning mode Peak hopping/jumping Dwell time / acquisition point (per sweep) 10 ms Number of acquisition points / spectral peak 1 Number of sweeps per replicate measurement 3250 Total acquisition time per replicate measurement

~3 min Number of replicate measurements 10 Optimum measurement precision? ~0.1 % RSD DIFFERENT ACQUISITION TIMES FOR DIFFERENT ISOTOPES ? Sometimes used Higher # of counts accumulated for low-abundant isotope Cf. Poisson counting statistics Lower scan speed Cf. noisy source Compromise conditions QUADRUPOLE-BASED ICPMS IMPROVEMENT WITH A COLLISION/REACTION CELL Use of Ne as non-reactive collision gas in DRC Mixing of ions sampled at slightly different moments in time Collisional damping improved isotope ratio precision

L. Moens et aI, JAAS, 16, 991994, 2001. QUADRUPOLE-BASED ICPMS IMPROVEMENT WITH A COLLISION/REACTION CELL Use of Ne as non-reactive collision gas in DRC Mixing of ions sampled at slightly different moments in time Collisional damping improved isotope ratio precision Increased mass discrimination Improved isotope ratio precision laser ablation M. Resano et al, JAAS, 23, 1182-1191, 2008. QUADRUPOLE-BASED ICPMS EQUIPPED WITH A COLLISION/REACTION CELL Other guidelines are still valid Low dwell time / acquisition point

1 acquisition point / spectral peak Acquiring a sufficiently high # of pulses Sufficiently target element concentration Sufficiently long measurement time per replicate L. Moens et aI, JAAS, 16, 991994, 2001. SECTOR FIELD ICP MASS SPECTROMETRY entrance slit MR HR LR exit slit Selection of resolution setting R = 300, 4000 or 10000 SECTOR FIELD ICP MASS SPECTROMETRY IMPROVED ISOTOPE RATIO PRECISION AT LOW R signal intensity 2500

analyte ion + molecular ion 2000 1500 1000 500 0 0 10 20 30 40 50 60 mass/charge (arbitrary units) Optimum measurement precision? ~0.025 0.05% RSD

HOW ARE FLAT-TOPPED PEAKS OBTAINED ? Width of ion beam < Exit slit width Wide exit slit Scanning HOW ARE FLAT-TOPPED PEAKS OBTAINED ? Width of ion beam < Exit slit width Wide exit slit Scanning HOW ARE FLAT-TOPPED PEAKS OBTAINED ? Width of ion beam < Exit slit width Wide exit slit Scanning

SECTOR FIELD ICP MASS SPECTROMETRY IMPROVED ISOTOPE RATIO PRECISION AT LOW R Vanhaecke et al., Anal. Chem., 567-569, 68, 1996 ! central section of flat-topped peak SECTOR FIELD ICP MASS SPECTROMETRY IMPROVED ISOTOPE RATIO PRECISION AT LOW R Vanhaecke et al., Anal. Chem., 567-569, 68, 1996 SECTOR FIELD ICP MASS SPECTROMETRY ISOTOPE RATIO PRECISION AT MEDIUM R ? signal intensity 2500 analyte ion + molecular ion

2000 flat-topped peaks 1500 RSD% 0.05% 1000 500 0 0 250 20 30 40 50 60 mass/charge (aribitray units)

analyte ion 200 signal intensity 10 triangular peaks 150 RSD% 0.1% 100 molecular ion 50 0 0 10 20

30 40 mass/charge (arbitrary units) 50 SECTOR FIELD ICP MASS SPECTROMETRY ISOTOPE RATIO PRECISION AT MEDIUM R ? Vanhaecke et al., Anal. Chem., 268-273, 69, 1997 ! ION DETECTION VIA ELECTRON MULTIPLIER CONTINUOUS DYNODE EM multiplication effect - 2000 V avelanche of electrons 7 8 multiplication factor: 10 - 10 pulse counting mode vs. analog mode

ION DETECTION VIA ELECTRON MULTIPLIER DISCRETE DYNODE EM cathode avelanche multiplication effect of electrons ion signal secondary electron discrete dynodes at successively higher potential 7 8 multiplication factor: 10 - 10 pulse counting mode vs. analog mode DETECTOR DEAD TIME EM OPERATED IN PULSE COUNTING MODE Handling of one ion no possibility to detect another one

10 100 ns More pronounced effects at higher count rates Accurate isotope ratio ( 1) determination requires correction Correction for non-paralyzable detector: Experimental determination of dead time () required Various methods for determination Do not forget to set = 0 in software prior to experimental determination Detector dead time instrument software for automatic correction DETERMINATION OF DETECTOR DEAD TIME Normalized 208 207 208 207 208 207 Pb/ Pb isotope ratio (= ( Pb/ Pb)measured/( Pb/

Pb)true value) plotted as a function of the value applied for dead time correction of the raw results obtained for solutions with a Pb concentration ranging from 20 to 45 g/L. In this particular case, the dead time of the detection system was observed to be 20 ns. F. Vanhaecke et al, JAAS, 13, 567571, 1998. DETERMINATION OF DETECTOR DEAD TIME Variation of the 204 208 Pb/ Pb isotope ratio as a function of the Pb concentration for various assumed values of detector dead time. S. M. Nelms et al, JAAS, 16, 333-338, 2001. DETERMINATION OF DETECTOR DEAD TIME S. M. Nelms et al, JAAS, 16, 333-338, 2001 Slope of the curve obtained on plotting the 204 208

Pb/ Pb isotope ratio vs. the Pb concentration as a function of the assumed value for the detector dead time. The intersection of the line thus obtained with the x-axis provides the actual dead time. TIME-OF-FLIGHT ICP MASS SPECTROMETRY t1 t0 t2 + + + + + + Acceleration (V)V) field-free flight tube

introduction of package of ions into TOF-analyzer detection time interval required for mass analysis TIME-OF-FLIGHT ICP MASS SPECTROMETRY acceleration E2 reflectron or E1 detector ion, mass m, E2 ion, mass m, E1 E2 > E1 ion mirror

ISOTOPE RATIO PRECISION WITH TIME-OF-FLIGHT ICP MASS SPECTROMETRY Vanhaecke et al., Anal. Chem., 71, 3297-3303,1999. Handling of ions sampled at the same time Improvement in isotope ratio precision to 0.05% RSD Analog detection mode use of signal at m/z = 210 for normalization of background (subtraction) 30 s measurement time per replicate PRECISION, PRECISION, WHAT ABOUT ACCURACY ? MASS DISCRIMINATION IN ICPMS Mass discrimination Measured ratio true value Order of magnitude ca. 1% per mass unit @ mid-mass Considerably larger @ low masses ICPMS Not a systematic f(time) NOT = mass fractionation !

TIMS First TIMS measurement result < true value Later on: measurement result > true value F. Albarede and B. Beard, Rev. Miner. Geochem., 55, 113150, 2004. MASS DISCRIMINATION IN ICPMS Transmission efficiency: T(Mk) = nk/Nk nk: # of ions with m/z = k detected Nk: # of atoms with m/z = k formed in ion source Modern MS instruments Transmission efficiency in flight tube 100% Conversion ion signal = independent of m/z Mass discrimination in ICPMS?

Space-charge effects in interface Behind skimmer F. Albarede and B. Beard, Rev. Miner. Geochem., 55, 113150, 2004. SPACE-CHARGE EFFECTS IN THE ICPMS INTERFACE All ions forced to move with vAr (collisions) Ekin = mv2 and hence, f(mion) Electrostatic repulsion between positively charged ions Defocusing of ion beam Lighter ions preferentially lost MASS DISCRIMINATION CORRECTION IN SINGLE-COLLECTOR ICPMS External correction Based on comparison of experimental result and certified value for isoropic reference material Preferably via bracketing (std sample std sample ) Isotope ratio result 1,2 1,15

1,1 1,05 1 isotopic standard sample 0,95 0 1 2 3 4 5 6

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Measurement number MASS DISCRIMINATION CORRECTION IN SINGLE-COLLECTOR ICPMS Internal correction type I If at least one isotope ratio of the target element is constant in nature E.g., Sr: isotopic composition displays natural variation, but 86 88 Sr/ Sr = constant Comparison of experimental result and certified value for 86 88

Sr/ Sr Calculation of correction factor or , to be used for further correction R true K 1 linear m R obs K R true 1 power R obs R true m1 K R obs m 2 m

R true m K e exponential R obs Various approaches lead to similar results (no significant differences) MASS DISCRIMINATION CORRECTION IN SINGLE-COLLECTOR ICPMS Internal correction type II Using an element, close in mass number, added to the sample E.g., Tl added to sample solutions intended for Pb isotopic analysis Comparison of experimental result and certified value for 203 205 Tl/ Tl Calculation of correction factor or , to be used for further correction

R true K 1 linear m R obs K R true 1 power R obs R true m1 K R obs m 2 m R true m K

e exponential R obs Various approaches lead to similar results (no significant differences) ISOTOPE RATIO PRECISION WITH ICPMS (OPTIMUM VALUES) Type of ICPMS instrument Internal isotope ratio precision (RSD) Traditional quadrupole-based ICPMS 0.1% Quadrupole-based ICPMS 0.025% with pressurized collision/reaction cell Time-of-flight ICPMS Single-collector sector field ICPMS Multi-collector ICPMS

0.025% 0.025% 0.002% at LR and 0.005% at MR Applications Induced variations single-collector Natural variations due to radiogenic nuclide Geochronological dating multi-collector Provenance determination single- & multi-collector at LR and 0.1% at MR Natural variations due to fractionation multi-collector Natural variations due to extinct radionuclides multi-collector INDUCED VARIATON ELEMENTAL ASSAY VIA ISOTOPE DILUTION

PRINCIPLE OF ISOTOPE DILUTION (ID) R signal isotope 2 blend = 0.688 signal isotope 1 25 R tracer = 0.208 20 15 R

sample = 2.125 10 5 0 sample + spike = mixture PRINCIPLE OF ISOTOPE DILUTION (ID) sample spike

mixture mixture = known amount of sample + known amount of spike spike : different isotopic composition determination of ratio (enriched isotope / reference isotope) in: sample spike mixture Isotope ratios:much more more robust than signal intensities ! ELEMENTAL ASSAY USING ISOTOPE DILUTION 1 1 1 Rsample 2 Rspike 2 Rmixture 2 nsample

nsample nspike nspike 1 spike enriched in n 1 nsample1nspike Rmixture 1 nsample Rsample 1 nspike Rspike

Rsample Rspike Rmixture 1 . nspike nsample . Rspike Rmixture Rsample 1 1 nspike spike(1) . nspike 1 nsample nsample sample(1) nsample1nspike nsample2 nspike ELEMENTAL ASSAY USING ISOTOPE DILUTION 1 R sample 2

spike nsample nsample R spike 2 enriched in nspike nspike 1 R mixture 2 nsamp 1 nspike (1) . nspike spike nsample 2 nspike

1 n enriched in nsample 2 n R spike R mixture 2 . nspike Rmixture R sample 2 2 nsample 1nspike R sample R spike R mixture 1 . nspike

. R spike Rmixture R sample 1 2 1 nspike spike ( 2) . n spike optimum and nsample R mixture R sample . R spike n sample sample ( 2) ELEMENTAL ASSAY USING ISOTOPE DILUTION Advantages After isotopic equilibration: analyte losses do no affect result

Isotope ratios barely affected by changes in sensitivity (matrix effects) Most reliable calibration method High accuracy High precision Disadvantages Not suited for mono-isotopic elements Be, Na, Al, P, K, Sc, Mn, Co, As, Y, Nb, Rh, I, Cs, Pr, Ho, Tm, Au, Bi, Th Sometimes : use of long-lived radionuclide (e.g., 129I) High purchase price of spikes 500-1000 US $ / 100 mg Isotopic enrichment & nuclide (natural isotopic abundance) Analyte concentration has to be approximately known Use of IDMS ? Reference measurements Analyte losses to be expected ELEMENTAL ASSAY USING ISOTOPE DILUTION 1. Natural variations in isotopic composition Radiogenic isotopes (Sr, Pb)

1 Anthropogenic effects (Li, Pu, U) Isotope fractionation (light elements) 2 Extra-terrestrial materials 2. Reverse isotope dilution Spike of natural isotopic composition 3. 3 Estimation of C by conventional techniques Optimization of sample/spike ratio Appropriate signal intensities P. Evans et al, JAAS, 16, 964969, 2001. DETERMINATION OF ULTRA-TRACE AMOUNTS OF

FE IN AGNO3 SOLUTIONS Goal? Determination of Fe in AgNO3 solutions Ag-matrix: ~ 600 g.L-1 Ag memory effects & signal suppression ICPMS: max. ~ 100 mg.L-1 Ag dilution of the samples (external calibration) LOD = 1200 ng.g-1 precipitation of Ag as AgBr co-precipitation of Fe? isotope dilution as a calibration method L; Balcaen et al, ABC, 377, 1020-1025, 2003.. DETERMINATION OF FE IN AGNO3 SOLUTIONS PRECIPITATION OF AG+ AS AGBR + ID 100 54

56 90 80 % abundancy 70 60 50 40 30 20 10 0 sample spike after equilibration of sample and spike loss of material does not effect the result mixture DETERMINATION OF FE IN AGNO3 SOLUTIONS PRECIPITATION OF AG+ AS AGBR + ID 54 Fe spike

HBr AgNO3 precipitation of Ag Filtration Dilution (50x) Ag-content: 1 mg.L-1 !! CONTAMINATION !! L; Balcaen et al, ABC, 377, 1020-1025, 2003.. DETERMINATION OF FE IN AGNO3 SOLUTIONS SPECTRAL INTERFERENCES Fe (5,85 %) 54 Isobaric nuclide Ar-containing

molecular ion 54 Ar14N+ 38 Ar16O+ 36 Ar18O+ 40 Fe (0,28 %) 58 Ni+ 58 Ar16O+ 40 Ca16O+ 40

40 40 37 Fe (2,12 %) 57 Cr+ Ca-containing molecular ion Cl-containing molecular ion Fe (91,8 %) 56 Cl16OH+ Ar16OH+ 38

Ar18OH+ 40 Ar18O+ Ca16OH+ 40 Ca18O+ 42 Ca16O+ Na35Cl+ 23 L; Balcaen et al, ABC, 377, 1020-1025, 2003.. DETERMINATION OF FE IN AGNO3 SOLUTIONS OVERCOMING SPECTRAL OVERLAP VIA CHEMICAL RESOLUTION PerkinElmer-SCIEX Dynamic Reaction Cell ICP-MS

Use of NH3 to induce selective ion-molecule reactions allowing spectral overlap to be overcome at m/z = 54 & 56 L; Balcaen et al, ABC, 377, 1020-1025, 2003.. DETERMINATION OF FE IN AGNO3 SOLUTIONS OVERCOMING SPECTRAL OVERLAP VIA CHEMICAL RESOLUTION 50 g/L Fe std soln 1 mg/L Ca std soln S/B ratio m/z = 56 L; Balcaen et al, ABC, 377, 1020-1025, 2003.. DETERMINATION OF ULTRA-TRACE AMOUNTS OF FE IN AGNO3 SOLUTIONS Comparison of LODs Dilution of sample solution

1200 ng/g AgBr precipitation + ID 10 ng/g L; Balcaen et al, ABC, 377, 1020-1025, 2003.. OTHER QUADRUPOLE-BASED INSTRUMENTS EQUIPPED WITH A COLLISION/REACTION CELL Agilent 7700 (octopole set-up) ThermoScientific Xseries 2 (hexapole set-up) ISOTOPE DILUTION IN ELEMENTAL SPECIATION ANALYSIS SPECIES-SPECIFIC ISOTOPE DILUTION What? Synthesis of specific compound with non-natural isotopic composition Addition of this compound to sample As early as possible in the analysis process Advantages ? Automatic correction for:

Non-quantitative derivatization (if relevant, e.g., GC-ICPMS) Non-quantitative extraction (if relevant, e.g., SPME) Non-quantitative column recovery Variations in ICPMS sensitivity due to Matrix effects Gradient elution Signal drift Instrument instability Important remark No correction for non-quantitative recovery out of solid matrix ISOTOPE DILUTION IN ELEMENTAL SPECIATION ANALYSIS SPECIES-UNSPECIFIC ISOTOPE DILUTION When ?

No standards available Identity of species not known Too many species to synthesize them all Species too complicated to synthesize Synthesis of standards too labour-intensive and/or time-consuming Advantages ? Automatic correction for changes in ICPMS sensitivity Gradient elution Matrix changes as f(time) Signal instability & drift ISOTOPE DILUTION IN ELEMENTAL SPECIATION ANALYSIS SPECIES-UNSPECIFIC ISOTOPE DILUTION K.G. Heumann

BR-CONTAINING DRUG: HPLC-ICPMS METABOLITE PROFILING QUANTIFICATION VIA SPECIES UNSPECIFIC ISOTOPE DILUTION sample 79 C18 column HPLC pump injection port Br + 81 Br ICP gradient elution Fase A: aqueous phase Fase B: 45% MeOH + 45% ACN isotopically

HPLC effluent ICPMS enriched standard 81 Br-standard solution F. Cuyckens et al, ABC 390, 17171729, 2008. BR-CONTAINING DRUG: HPLC-ICPMS METABOLITE PROFILING QUANTIFICATION VIA SPECIES UNSPECIFIC ISOTOPE DILUTION 200000 79Br 81Br 180000 160000 Intensity (cps) 140000

120000 100000 80000 60000 40000 20000 0 0 1000 2000 3000 4000 5000 6000 time (s) F. Cuyckens et al, ABC 390, 17171729, 2008. BR-CONTAINING DRUG: HPLC-ICPMS METABOLITE

PROFILING QUANTIFICATION VIA SPECIES UNSPECIFIC ISOTOPE DILUTION 12 10 6 81 81 79 Br/ Br 8 4 Br / 79 Br

Rnat 1 Rspike 9 2 0 35 40 45 50 55 60 time (min) Via ID formula mass flow chromatogram F. Cuyckens et al, ABC 390, 17171729, 2008. BR-CONTAINING DRUG: HPLC-ICPMS METABOLITE PROFILING

QUANTIFICATION VIA SPECIES UNSPECIFIC ISOTOPE DILUTION Mixture of standards mass flow chromatogram g Br /s F. Cuyckens et al, ABC 390, 17171729, 2008. INDUCED VARIATION TRACER EXPERIMENTS WITH STABLE ISOTOPES STABLE ISOTOPIC TRACER EXPERIMENTS What ? Use of stable isotopic tracer(s) to study Physical processes, (bio)chemical reactions, Why tracers? Example: study of transport of element through membrane Compartment 1 Compartment 2

M M Compartment 1 Compartment 2 M M can be studied via can NOT be studied via element determination as f(time) element determination as f(time) TRACER EXPERIMENTS FOR STUDYING THE TRANSPORT OF MG THROUGH THE INTESTINAL EPITHELIUM OF TILAPIA I intestinal epithelium

lumen 26 Mg blood 24 2+ Mg 2+ medium contains substantial amounts of C, Na, P, S, Cl, K and Ca 0.5 mmole Mg /L V G. De Wannemacker et al, JAAS, 16, 581-586, 2001. INTERFERENCE-FREE MEASUREMENT OF MG ISOTOPE RATIOS AT R = 3000 (SECTOR FIELD ICPMS)

signal intensity (arbitrary units) 24 Mg + (20 g/L Mg) 1200 1000 23 800 + 12 600 400 NaH (2 g/L NaCl) + C (2% EtOH) 2 48

2+ Ca (100 mg/L Ca) 200 0 23.95 23.97 23.99 24.01 mass-to-charge ratio G. De Wannemacker et al, JAAS, 16, 581-586, 2001. TRACER EXPERIMENTS FOR STUDYING THE TRANSPORT OF MG THROUGH THE INTESTINAL EPITHELIUM OF TILAPIA 26 24 Mg/ Mg

5 4.8 4.6 4.4 4.2 4 3.8 uncertainties indicated are 1s 3.6 tracer 0 min 20 min 50 min

isotope ratio precision : ~ 0.5% RSD (5 x 1 min) G. De Wannemacker et al, JAAS, 16, 581-586, 2001. TRACER EXPERIMENTS FOR STUDYING THE UPTAKE OF ZN BY DAPHNIA MAGNA Daphnia? Small aquatic crustaceans Often termed water fleas Due to swimming style Often used in aquatic toxicology Indicator of ecosystem health White mouse of ecotoxicology Easy to culture in the lab Consistent response to toxins Rapid reproduction Daphnia magna Freshwater invertebrate Large daphnid : L = up to 5 mm TRACER EXPERIMENTS FOR STUDYING THE UPTAKE OF ZN BY DAPHNIA MAGNA Usual assumption: Toxicity caused by waterborne metal only

Uptake via gills (A) Effect of dietary metals ignored Uptake via alimentary channel (B) Our study: Effects of dietary Zn ? Exposure experiment (total Zn / ICPMS) Reprocductive toxicity B A Relative importance of both exposure routes ? Stable isotopic tracer experiment (ICPMS) TRACER EXPERIMENTS FOR STUDYING THE UPTAKE OF ZN BY DAPHNIA MAGNA 67 Zn 2+ Zn (aq)

Zn isotopic analysis using sector field ICPMS 68 Zn At R = 4000 L. Balcaen et al, ABC, 390, 555569, 2008. TRACER EXPERIMENTS FOR STUDYING THE UPTAKE OF ZN BY DAPHNIA MAGNA 67 2+ Zn (aq) Zn 68 Zn 68

+ excess Zn-EDTA 67 to minimize effect of Zn leaching from algae L. Balcaen et al, ABC, 390, 555569, 2008. TRACER EXPERIMENTS FOR STUDYING THE UPTAKE OF ZN BY DAPHNIA MAGNA 100% water: 70 g/L 68 Zn + EDTA water: 70 g/L 68 Zn algae: 67 Zn algae:

67 Zn water: 150 g/L 68 Zn water: 300 g/L 68 Zn Isotopic abundance (%) 80% 60% 40% algae: 67 Zn natural

Zn algae: 67 Zn 70 68 67 66 64 20% 0% 502 566 571 576 581 Sample number

L. Balcaen et al, ABC, 390, 555569, 2008. TRACER EXPERIMENTS FOR STUDYING THE UPTAKE OF ZN BY DAPHNIA MAGNA Zn concentration in daphnia magna (g/g) 80.0 70.0 67 68 Total Zn 60.0 50.0 40.0 in contact with: - algae: 67Zn - water: 70 g/L 68Zn in contact with: - algae: 67Zn - water: 150 g/L 68Zn in contact with:

- algae: 67Zn - water: 300 g/L 68Zn in contact with: - algae: 67Zn - water: 70 g/L 68Zn + EDTA 30.0 20.0 10.0 0.0 566 571 576 581 Sample number L. Balcaen et al, ABC, 390, 555569, 2008. HUMAN HEALTH ESSENTIAL ELEMENTS Essential elements? Deficiency reproducible deficiency syndrome

Physiological and/or structural deviations Administration prevents or cures deviation Beware! Also an essential element is toxic at too high concentrations Health condition Optimal Marginal Intoxication Lethal Lethal Uptake FE AS AN ESSENTIAL ELEMENT Lungs veins arteries Tissues

Muscles FE AS AN ESSENTIAL ELEMENT DEFICIENCY? Low Fe intake ? First Fe stored in the body is consumed for maintaining a normal blood level when the storage sites of iron are deficient iron deficiency anemia Storage sites: liver hepatocytes, bone marrow and spleen Reasons for Fe deficiency ? Low dietary intake inadequate absorption of Fe excessive blood loss Symptoms of iron deficiency anemia: feeling tired and weak decreased work and school performance slow cognitive and social development during childhood difficulty maintaining body temperature decreased immune function, which increases susceptibility to infection

glossitis (an inflamed tongue) Importance of Fe deficiency (WHO) ? 80% of the world's population may be iron deficient 30% may have iron deficiency anemia Fe supplements ? Who? How much? Efficiency? FE AS AN ESSENTIAL ELEMENT TOXICITY? Homeostasis Regulation of internal environment to maintain a stable, constant condition by adapting the uptake according to the prevailing conditions Fe toxicity excessive Fe intake? Body can reduce Fe absorption, but not to zero Iron toxicity if circulating Fe > transferrin (transport protein) Large amounts of free iron in circulation Cell damage: liver, heart and other metabolically active organs High excess of iron can damage intestinal lining even more iron can enter the bloodstream (can be lethal) Fe toxicity when? Genetic diseases, e.g., haemochromatosis

hereditary iron storage disease Too much Fe is stored, leading to chronic damage to important organs Prolonged unnecessary intake of Fe supplements Repeated blood transfusions Other causes STUDY OF UPTAKE OF FE IN RBC USING SINGLE TRACER APPROACH 2 1 54 Fe 1. Determination of Fe isotopic composition 2. Oral administration of 3.

Sampling of blood 4. 3 Sampling of basal blood 54 Fe tracer After 10 14 days time required for incorporation of Fe into RBC Determination of Fe isotopic composition Calculation of fraction of Fe absorbed DISADVANTAGES OF SINGLE TRACER APPROACH Single tracer approach does not take into account:

Redistribution over other body compartments Sometimes not or not accurately known E.g., Fe: Non-pregnant subject: 86 93% of Fe taken up RBC Pregnant female: fraction incorporated into RBC decreased to ~65% Dual tracer experiment For elements having 3 isotopes One orally administered tracer One intravenously administered tracer Intravenous tracer: 100% uptake Assumption once present in blood, both tracers will be redistributed identically STUDY OF UPTAKE OF FE IN RBC USING DUAL TRACER APPROACH 1 Basal blood sample 2 54 Fe Administration of

54 oral tracer ( Fe) 57 Intravenous tracer ( Fe) 3 57 Fe After 10 14 days PHARMACOKINETIC STUDY OF UPTAKE OF FE INTO SERUM USING DUAL TRACER APPROACH Oral administration of 54Fe, intravenous administration of 57Fe MS determination of: Fe/56Fe isotope ratio as f(time) = line A 57 Fe/56Fe isotope ratio as f(time) = line B 54 Log (enrichment)

time P.G. Whittaker et al, Analyst, 114, 675-678, 1989. DUAL TRACER TECHNIQUE IN STUDIES OF MINERAL METABOLISM Not accessible in case of human test objects PRACTICAL ISSUES OF TRACER EXPERIMENTS FOR ASSESSING THE UPTAKE OF MINERAL ELEMENTS How much tracer needs to be used? Analytical considerations Isotope ratio at time t needs to be significantly from initial ratio (Isotope ratio)t > (isotope ratio)i + 3s(isotope ratio)i Higher precision lower amount of isotopic tracer suffices Determination of typical isotope ratio precision required Biomedical considerations What fraction of orally administered element is expected to be taken up? Dose administered should not be >> normal daily intake Financial considerations

Most expensive of the two tracers: administered intravenously Lowest amount required Price ~ isotopic entrichment e.g., 90% vs. 99% Price ~ natural isotopic abundance Typical price: 500-1000 US $ / 50 mg NATURAL VARIATION MULTI-COLLECTOR ICP MASS SPECTROMETRY MULTI-COLLECTOR ICP MASS SPECTROMETRY Isotope ratio precision: down to 0,002 % RSD ! ARRAY OF FARADAY COLLECTORS: SIMULTANEOUS MONITORING OF ION SIGNAL INTENSITIES signal intensity Isotope ratio 1.2 Isotope ratio precision:

390 1 370 350 0.8 330 0.6 310 0.4 290 isotope 1 isotope 2 270 0.2 isotope ratio 250

0 1 2 3 4 5 6 7 measurement number Simultaneous monitoring:

Automatic correction for signal instability & signal drift Higher isotope ratio precision With ICPMS instrument equipped with only one detector: Mimiced by fast hopping 8 9 10 down to 0,002 % RSD ! ION BEAMS FARADAY COLLECTORS ? Moveable detectors Zoom optics (motorized) The ion beams are steered into the appropriate collectors by applying suitable voltages on the zoom optics (= electrostatic lenses).

The position of the Faraday collectors can be optimised with respect to Or a combination of both the respective ion beams FARADAY COLLECTOR OPERATING PRINCIPLE ion beam Compared to electron multiplier: R = 10 11

V Analog amplifier Less sensitive No detector dead time Very long lifetime e - MULTI-COLLECTOR ICP MASS SPECTROMETRY Dedicated tool for highly precise isotopic analysis Competitor for thermal ionization mass spectrometry TIMS Advantages compared to TIMS ? Ion source operated at atmospheric pressure Straightforward sample introduction Contnuous pneumatic nebulization Laser ablation (bulk & spatially resolved analysis of solid samples) High ionization efficiency TIMS: formation of M+ ions limited to elemnts with IE < 7.5 eV Higher sample throughput Isolation of target element not required ??

MASS DISCRIMINATION IN MULTI-COLLECTOR ICP MASS SPECTROMETRY Same phenomenon as in single-collector ICPMS Due to high precision: Matrix exerts measurable influence on mass discrimination isolation of analyte element Analyte concentration exerts influence on mass discrimination Matching of target element concentrations within 30% INFLUENCE OF TARGET ELEMENT CONCENTRATION ON MASS DISCRIMINATION Element concentration measurably affects isotope ratio in MC-ICPMS Close matching (within 30%) between c(sample soln) and c(ext standard soln) Source: Alabrde and Beard, Analytical methods for non-traditional isotopes, chapter 4 in Geochemistry of non-traditional stable isotopes, eds. C.M. Johnson, B.L. Beard and F. Albarde, Reviews in Mineralogy & Geochemistry, Vol. 55, 2004. MASS DISCRIMINATION CORRECTION IN MULTI-COLLECTOR ICPMS If high precision & accuracy is required: Isolation of target element pure & quantitative

Matching of element concentration in samples & standards within 30% External correction Based on comparison of experimental result and certified value for isoropic reference material Bracketing (std sample std sample ) Internal correction type I If at least one isotope ratio of the target element is constant in nature E.g., Sr: isotopic composition displays natural variation, but 86 88 Sr/ Sr = constant Comparison of experimental result and certified value for 86 Sr/ 88 Sr Calculation of correction factor or , to be used for further correction Internal correction type II

Using an element, close in mass number, added to the sample E.g., Tl added to sample solutions intended for Pb isotopic analysis Comparison of experimental result and certified value for 203 Tl/ 205 Tl Calculation of correction factor or , to be used for further correction INTERNAL MASS DISCRIMINATION CORRECTION IN MULTI-COLLECTOR ICPMS Linear law model Exponential law model Russells equation R true K 1 power R obs

m R true ex ponentialm K e R obs R true m1 K R obs m 2 Significant differences !! Power law model R true K 1 linear m R obs

INTERNAL MASS DISCRIMINATION CORRECTION IN MULTI-COLLECTOR ICPMS No MD MD according to linear law (lin = 0.01) MD according to power law (power = 0.01) MD according to expontial law (exp = 0.01) MD according to Russells equation ( = -1.11053) 110/111 Rexp/Rtrue 110/112 Rexp/Rtrue 110/113 Rexp/Rtrue 110/114 Rexp/Rtrue 110/116

Rexp/Rtrue 1 0.99010 1 0.98039 1 0.97087 1 0.96154 1 0.94340 0.99010 0.98030 0.97059 0.96098 0.94205

0.99005 0.98020 0.97045 0.96079 0.94176 0.99000 0.98019 0.97056 0.96111 0.94272 Application of various correction methods Will result in relatively small differences Significant threat in precise isotope ratio work Still issue of discussion between specialists

INTERNAL MASS DISCRIMINATION CORRECTION IN MULTI-COLLECTOR ICPMS Internal correction type II Tl added to sample solutions intended for Pb isotopic analysis Further refinement: deduction of correction factor (Pb) via (Tl) Linear relationship between (Pb) and (Tl) defined via reference solutions SPECTRAL INTERFERENCES IN MULTI-COLLECTOR ICP MASS SPECTROMETRY? Usually: target element isolated from matrix Clean-up of spectrum No analyte isolation in case of laser ablation for sample introduction Ar introduced @ 20 L/min in ICP Ar+ Ar2+ Ar-containing molecular ions ArH+, ArN+, ArO+, ArOH+, Isotope ratio determination At least two nuclides free from spectral overlap

High precision Down to 0.002% RSD Limited contribution of interfering ion, already dramatic ! In contrast to situation for element determination FULL HIGH RESOLUTION IN MULTI-COLLECTOR ICPMS? Single-collector ICPMS Multi-collector ICPMS signal intensity 2500 analyte ion + molecular ion 2000 1500 1000 500 0 0 Low R

20 30 40 50 60 mass/charge (aribitray units) 250 analyte ion 200 signal intensity 10 Deteriorated isotope ratio precision 150

! 100 molecular ion 50 0 High R 0 10 20 30 40 mass/charge (arbitrary units) 50 PSEUDO HIGH RESOLUTION IN MULTICOLLECTOR ICPMS

THE BEST OF TWO WORLDS signal intensity 2500 analyte ion + molecular ion 2000 Low mass R down to 0.002% RSD 1500 1000 500 0 0 10 20 30 40

50 60 mass/charge (aribitray units) 700 Pseudo high mass R signal intensity 600 500 analyte ion 400 analyte ion + molecular ion 300 reduced entrance slit width exit slit width not changed

molecular ion 200 Interference-free measurement down to 0.005% RSD 100 0 0 10 20 30 40 mass/charge (arbitrary units) 50 60

MASS SPECTRAL PEAK SHAPES PSEUDO-HIGH MASS RESOLUTION Wide exit slit Narrow entrance slit Only side moved ! Scanning Analyte ion Interfering ion only MASS SPECTRAL PEAK SHAPES PSEUDO-HIGH MASS RESOLUTION Wide exit slit Narrow entrance slit Only side moved ! Scanning Analyte ion

Interfering ion only MASS SPECTRAL PEAK SHAPES PSEUDO-HIGH MASS RESOLUTION Wide exit slit Narrow entrance slit Only side moved ! Scanning Analyte ion Interfering ion only MASS SPECTRAL PEAK SHAPES PSEUDO-HIGH MASS RESOLUTION Wide exit slit Narrow entrance slit Only side moved ! Scanning

Analyte ion Interfering ion only MASS SPECTRAL PEAK SHAPES PSEUDO-HIGH MASS RESOLUTION Wide exit slit Narrow entrance slit Only side moved ! Scanning Analyte ion Interfering ion only MASS SPECTRAL PEAK SHAPES PSEUDO-HIGH MASS RESOLUTION Wide exit slit Narrow entrance slit Only side moved !

Scanning Analyte ion Interfering ion only MASS SPECTRAL PEAK SHAPES PSEUDO-HIGH MASS RESOLUTION Wide exit slit Narrow entrance slit Only side moved ! Scanning Analyte ion Interfering ion only MASS SPECTRAL PEAK SHAPES PSEUDO-HIGH MASS RESOLUTION Wide exit slit

Narrow entrance slit Only side moved ! Analyte ion Interfering ion only Scanning PSEUDO HIGH RESOLUTION IN MULTICOLLECTOR ICPMS EXAMPLE: MEASUREMENT OF FE ISOTOPE RATIOS Spectral scan Static collection Interference-free measurement of Fe isotope ratios Static multi-collection at m/z values where only analyte ions contributes to signal intensity S. Weyer, & J.B. Schwieters, Int. J. Mass Spectrom., 226, 355368, 2003 NATURAL VARIATION APPLICATIONS BASED ON RADIOGENIC NUCLIDES NATURAL VARIATIONS IN THE ISOTOPIC

COMPOSITION OF SR Variations in Sr isotopic composition due to: 87 Rb 87 Sr 87Rb = naturally occurring, long-lived radionuclide T1/2 = 48.8 x 109 y Isotopic composition of Rb has changed through time Isotopic composition odf Rb presently equal for all terrestrial materials Isotopic composition of Sr: variable! E.g., rocks: dependent on elemental Rb/Sr ratio + age Sr isotope Natural range of relative isotopic abundance 0.55 0.58 % 9.75 9.99 % 6.94 7.14 % 82.29 82.75 % 84 Sr Sr 87 Sr 88

Sr 86 IUPAC, 1997 NATURAL VARIATIONS IN THE ISOTOPIC COMPOSITION OF SR Pronounced variation! Measurable by TIMS MC-ICPMS Single-collector ICPMS Sr isotopic analysis useful for: Provenance determination Agricultural products Wine, cheese, Human remains quite often with single-collector ICP-MS Archeological findings Forensics

Geological dating - Rb-Sr dating very seldom with single-collector ICP-MS RADIOMETRIC DATING based on half-life (T1/2) of radionuclide and ratio of parent nuclide to daughter nuclide RB-SR DATING 87 Rb 87 Sr , with T1 / 2 48.8 10 9 y , or ln 2 1.42 10 11 T1 / 2 Possibilty for dating (t-determination) Igneous & metamorphic rocks, via Rb-rich minerals they contain whole rock dating Production of 87Sr as function(t): 87

Sr 87 Sr i 87 Rb ( e t 1 ) Absolute isotope amounts are difficult to determine accurately Divide left & right side by 86Sr Note: 86Sr does not vary as function(t) 87 87 Sr 87 Sr Rb ( e t 1 ) 86 86 86

Sr Sr i Sr 86 Sr 87 Sr 1 t lnequation 1 87 Resolve for 86t: Rb Sr

87 Sr 86 Sr i RB-SR DATING Based on: 1 t ln 1 86 Sr 87 Rb 87 Sr

86 Sr 87 Sr 86 Sr i Needed? Rb/Sr elemental ratio Traditionally determined via IDMS (accuracy & precision) 87Sr/86Sr isotope ratio TIMS, MC-ICPMS, ICPMS (87Sr/86Sr)initial Condition? System has always been closed with respect to Rb & Sr

In practice? Isochron dating RB-SR ISOCHRON DATING 87 Sr 86 Sr 87 Sr 86 Sr i 87 Rb t

( e 1) 86 Sr Is equation for straight line: y = ax + b With y = 87Sr/86Sr and x = 87Rb/86Sr isochron RB-SR ISOCHRON DATING IN PRACTICE t Da ts oin p a ne mi for

ral ron ch o s ni so Slope = (et 1) t rock age (t) Extrapolation intersection w Y-axis for x = 0 ( 87 86 Sr/ Sr)i PROVENANCE DETERMINATION VIA SR ISOTOPIC ANALYSIS Varying geology Varying Sr isotopic composition Sr isotopic composition, same for: Rocks Soil Vegetation Cattle .

NATURAL VARIATIONS IN THE ISOTOPIC COMPOSITION OF SR PROVENANCE DETERMINATION OF AGRICULTURAL PRODUCTS Transfer of Sr without measurable isotopic fractionation NATURAL VARIATIONS IN THE ISOTOPIC COMPOSITION OF SR PROVENANCE DETERMINATION OF AGRICULTURAL PRODUCTS Provenancing agricultural products ? To detect incorrect indication of geographical origin (fraud) Which products? Of plant origin: Wine: Almeida & Vasconselos, JAAS, 2001, Barbaste et al., JAAS, 2002 Cider: Garcia-Ruiz et al., ACA, 2007 Rice: Kawasaki et al., Soil Sci Plant Nutr, 2002 Ginseng: Choi et al., Food Chem, 2008

Asparagus: Swoboda et al.,ABC, 2008 Of animal origin: Cheese: Fortunato et al.,JAAS, 2004 Caviar: Rodushkin et al.,ACA, 2008 AUTHENTICATION OF KALIX (NE SWEDEN) VENDACE CAVIAR RODUSHKIN ET AL., ACA, 583, 310, 2007 87 86 Sr/ Sr: seasonal variation Kalix < geographical variation complemented with: trace element fingerprint Os isotopic analysis SR ISOTOPIC ANALYSIS OF FISH OTOLITHS FOR DISCOVERING FISH MIGRATION PATHS Otolith or ear bone Otolith or ear bone

Otoliths or "ear bones" consist of three pairs of small carbonate bodies that are found in the head of teleost (bony) fish. Otoliths are primarily associated with balance, orientation and sound detection, and function similarly to incus, malleus and stapes in the inner ear of mammals An otolith's ring structure can provide information about an individual's age, growth rate, and environment. In some cases, these patterns are a natural record; in other cases they are induced by man. SR ISOTOPIC ANALYSIS OF FISH OTOLITHS FOR DISCOVERING FISH MIGRATION PATHS Tree rings Fish otolith with growth rings Occurrence of growth rings Chronological archive Spatially resolved Sr isotopic analysis via laser ablation MC-ICPMS Reveals migration pathways with sub-annual resolution Outridge et al., Environ. Geol., 2002, 42, 891-899

NATURAL VARIATIONS IN THE ISOTOPIC COMPOSITION OF SR PROVENANCE DETERMINATION OF AGRICULTURAL PRODUCTS Transfer of Sr without measurable isotopic fractionation SR ISOTOPIC ANALYSIS FOR PROVENANCE DETERMINATION OF HUMAN REMAINS Enamel Formed during early childhood 87Sr/86Sr ~ food age 1 7 Dentine Continuously renewed Faster Sr turnover rate 87Sr/86Sr ~ food last years

Useful info Archaeology Forensics SR ISOTOPIC ANALYSIS FOR PROVENANCE DETERMINATION OF HUMAN REMAINS St-Servatius basilica Maastricht, Netherlands 1600 years of history Early christianity in the Maas valley Important archaeological excavations Analysis of the grave-field population Locals and/or immigrants? Sr isotopic analysis of tooth tissue & soil (UGent & ETH) Acid digestion of samples (open beaker HNO3 & HCl) Isolation of Sr using Sr-spec (Eichrom Technologies) Sr isotopic analysis using multi-collector ICP-MS SR ISOTOPIC ANALYSIS FOR PROVENANCE DETERMINATION OF HUMAN REMAINS 87

Sr / 86 dentine Sr enamel 0,7106 0,7104 0,7102 0,7100 0,7098 0,7096 0,7094 71-M

454-M I: incisor, M: molar 454-I 0,7090 108-M Pandhof population 108-I 0,7092 NATURAL VARIATIONS IN THE ISOTOPIC COMPOSITION OF PB 238U 206Pb 235U 207Pb 232Th 208Pb 204Pb: not radiogenic NATURAL VARIATIONS IN THE ISOTOPIC COMPOSITION OF PB Pb isotope Natural range of

relative isotopic abundance 1.04 1.65 % 20.84 27.48 % 17.62 23.65 % 51.28 56.21 % 204 Pb Pb 207 Pb 208 Pb 206 IUPAC, 1997 16 15 Pb 204 9

U: T1/2 = 4.5 x 10 y 235 8 U: T1/2 = 7.1 x 10 y 232 Th: T1/2 = 1.4 x 10 204 14 207 Pb/ 238 13 12 10

12 14 16 206 204 Pb/ Pb 18 20 10 Pb = not radiogenic y NATURAL VARIATIONS IN THE ISOTOPIC COMPOSITION OF PB

Pronounced variation! Measurable by TIMS, MC-ICPMS, single-collector ICPMS Pb in the earths crust Shows isotopic variation 206Pb/207Pb ~ 1.20 Pb in ores Ore formation separation of Pb from Th & Pb Isotopic compostion of Pb frozen mines show Pb isotopic composition: Time of ore deposit formation U/Pb, Th/Pb ratio in parent material Isotope ratio applications ? Distinction between crustal Pb & ore-Pb Distinction between Pb (ores) of different provenance PbS ore galena U,TH PB ISOTOPIC DATING First step = much slower than subsequent steps Condition of secular equilibrium Decay rate of parent superimposed on all daughters

single step behaviour Possibilty of dating cf. Rb-Sr dating 208 Pb 232 Th 208 Pb e 232 t 1 204 Pb 204 Pb 204 Pb i is oc hr on U,TH PB ISOTOPIC DATING Approach similar to Rb-Sr dating

U,TH PB ISOTOPIC DATING First step = much slower than subsequent steps Condition of secular equilibrium Decay rate of parent superimposed on all daughters single step behaviour Possibilty of dating cf. Rb-Sr dating 207 Pb 235 U 207 Pb e 235 t 1 204 Pb 204 Pb 204 Pb i U,TH PB ISOTOPIC DATING First step = much slower than subsequent steps Condition of secular equilibrium Decay rate of parent superimposed on all daughters

single step behaviour Possibilty of dating cf. Rb-Sr dating 206 Pb 238 U 206 Pb e 238 t 1 204 Pb 204 Pb 204 Pb i U,TH PB ISOTOPIC DATING 206 Pb 238 U 206 Pb e 238 t 1

204 Pb 204 Pb 204 Pb i 207 Pb 235 U 207 Pb e 235 t 1 204 Pb 204 Pb 204 Pb i 208 Pb 232 Th 208 Pb e 232 t 1

204 Pb 204 Pb 204 Pb i h 3 independent ages! h Identical (similar) results concordant dates actual age of mineral U,TH PB ISOTOPIC DATING Conditions for obtaining concordant age? Mineral has always been closed for: U, Th, Pb & all intermediate daughters Correct values for Pbi are used The decay constants 232, 235 and 238 are accurately known Isotopic composition of U is normal Not affected by 235U fission Measurements are error-free Limited application area

Losses of U, Th, Pb or intermediate daughters Facilitated by damage caused by radioactive decay (-decay) Often used for dating of marine carbonates (corals) Relatively high U (50-100 ppb), low Pb (100-500 ppb) contents Closed system behaviour U PB ISOTOPIC DATING Often: minerals behave as open systems Pb lost of same isotopic composition as Pb in mineral t 206 Pb 206 Pb 238 U (e 1) i 207 Pb 207 Pb 207 Pb * 235 U e i 206 206 Pb 206 Pb * 238 U Pb

e i 207 Pb 207 Pb 235 U (e 235 t 1) i 238 235 t 1 238 t 1 Based on Pb isotope ratio only (not affected by Pb loss) 235U/238U: constant for (practically) all terrestrial material U PB ISOTOPIC DATING

207 Pb 207 Pb 207 Pb * 235 U e 235 t 1 i 206 206 Pb 206 Pb * 238 U 238 t 1 Pb e i Equation cannot be simply solved for t Transcendental How to obtain t? Tables / graph: 207Pb/206Pb as a function of time Trial & error approach (iteration) via computer Graphical approach

Used for dating zircons (mineral) Retentive for U, Th, Pb & intermediate daughters Present in a large variety of rocks U PB ISOTOPIC DATING 0.6 (206 Pb/207 Pb)* 0.5 0.4 0.3 0.2 0.1 0 0 1 2 3 9 time (x 10 years)

h Graph: h Nowadays: computer approach (trial & error / iteration) 206 207 Pb/ Pb as a function of time 4 5 INTRODUCTION TO THE CONCORDIA DIAGRAM 206 Pb * 238 U 207 Pb * 235 U e 238 t 1 e 235 t 1

INTERPRETATION OF THE CONCORDIA DIAGRAM h All systems providing concordant dates plot on the concordia h As a mineral ages, it moves along the concordia ( ) 4 Closed system behaviour ! AGING OF A MINERAL ON THE CONCORDIA DIAGRAM EFFECT OF LOSS OF PB Sudden Pb loss event: Pb concentration Pb isotopic composition at t not affected USE OF CONCORDIA DIAGRAM FOR ROCK DATING DISCORDIA

h Several minerals of same rock loose various amounts of Pb at time t h Results for these minerals (at present) still plot on one line: Discordia h Higher intersection point with concordia = age of rock hosting the minerals h Lower intersection point = time passed since Pb loss event USE OF CONCORDIA DIAGRAM FOR ROCK DATING DISCORDIA Example h Age of rock hosting zircons = 3.56 billion years

h Pb loss event approx. 1.859 billion years ago h Complication in case of continuous loss! G. Faure, Principles of Isotope Geology USE OF CONCORDIA DIAGRAM FOR ROCK DATING DISCORDIA Example with U loss occurred ~0.6 billion yrs ago G. Faure, Principles of Isotope Geology PB ENVIRONMENTAL POLLUTION Pb in the atmosphere Geogenic background: crustal signature Pollution: ore signature possibility to calculate relative contributions 208

Pb/206Pb 2.10 2.09 2.08 Source 2 line ing Mix 2.07 Local, geogenic lead 2.06 Source 1 2.05 Pb added to gasoline (anti-knocking

2.04 0.825 agent) 0.830 0.835 0.840 207 Pb/ 206 Pb 0.845 0.850 0.855 PB ENVIRONMENTAL POLLUTION CALCULATION OF RELATIVE CONTRIBUTIONS

208 Pb/206Pb 2.10 2.09 2.08 Ac 2.07 Af f ect e ou ari ov t d s

l t ua s ple s am t en ext y sb the pr e c se n eo fp ol

etr -P b Source 2 Local, geogenic lead 2.06 2.05 Source 1 Pb added to gasoline (anti-knocking 2.04 0.825 agent) 0.830 0.835 0.840

207 Pb/206Pb 0.845 0.850 0.855 CONTRIBUTION OF PETROL-PB TO PB IN HIGH ALPINE SNOW 208Pb / 206Pb DRING ET AL., FRESENIUS J ANAL CHEM, 359, 382-384, 1997. 2.24 2 x standard error 2.22 European geogenic material

2.20 Broken Hill single-collector Sector-field ICP-MS Leaded gasoline CH Pb-levels low pg/g 5 ng/g 2.18 12 min / sample 2.16 PbMe4 & PbEt4 2.14 Leaded gasoline EUR 2.12 2.10

In leaded petrol 1995 - 1996 snow 2.08 2.06 0.84 0.86 0.88 0.90 207Pb 0.92 / 206Pb 0.94 as anti-knocking products 0.96

CASE STUDY PB POLLUTION IN MARINE SEDIMENTS NEAR CASEY STATION, ANTARCTICA Pollution established @ Brown Bay Townsend and Snape, JAAS, 17, 922-928, 2002. CASE STUDY PB POLLUTION IN MARINE SEDIMENTS NEAR CASEY STATION, ANTARCTICA Samples Grab samples + core samples Sample preparation Stored frozen Dried at 105oC Sieved to <2mm grain size Total digestion using concentrated mineral acids, including HF Measurement of Pb isotope ratios Single-collector sector field ICPMS 1200 scans in ~2 min 201Hg monitored to correct for potential isobaric interference on 204Pb

Correction for mass discrimination corrected using NIST SRM 981 Isotopic reference material Bracketing approach Townsend and Snape, JAAS, 17, 922-928, 2002. CASE STUDY PB POLLUTION IN MARINE SEDIMENTS NEAR CASEY STATION, ANTARCTICA Low Pb-level sediments local Pb Mixing line Broken Hill mining area Pb = potential source of contamination Townsend and Snape, JAAS, 17, 922-928, 2002. CASE STUDY PB POLLUTION IN MARINE SEDIMENTS NEAR CASEY STATION, ANTARCTICA Mixing line

The higher the Pb concentration, the closer the 208 204 Pb/ Pb ratio to the Broken Hill value Straight lines are preferred use 1/Pb instead CASE STUDY PB POLLUTION IN MARINE SEDIMENTS NEAR CASEY STATION, ANTARCTICA Background Pb Mixing line Townsend and Snape, JAAS, 17, 922-928, 2002. PB ENVIRONMENTAL POLLUTION MORE THAN TWO SOURCES 208 Pb/206Pb 2.10

2.09 Source 1 2.08 Source 2 2.07 2.06 2.05 2.04 0.825 Source 1 0.830 0.835 0.840 0.845

0.850 0.855 207 Pb/206Pb F. Vanhaecke et al, JAAS, 24, 863-886, 2009. PB ISOTOPIC ANALYSIS VIA MULTICOLLECTOR ICPMS PB INTOXICATION IN THE ROMAN ERA Valkenburg (NL) Roman settlement (Praetoria Agrippinae) 1st 3rd century AD Graveyard excavated Adults: cremated, ashes burried Babies & infants buried 92 remains of stillborn & babies (< 1 y) High levels of Pb in bone tissue 30 - 350 g/g vs. 4 g/g nowadays

Prenatal Pb intoxication or diagenesis? Pb isotopic analysis Bone tissue cf. graveyard soil Pb artifacts & garum Multi-collector ICPMS De Muynck et al, ABC, 390, 477486, 2008. PB ISOTOPIC ANALYSIS VIA MULTICOLLECTOR ICPMS PB INTOXICATION IN THE ROMAN ERA Sample digestion Microwave-assisted acid digestion using HNO3 + HCl bone & garum HNO3 + HCl + HF + HClO4 soil HNO3 (hot plate) Pb artifacts Isolation of Pb Pb-spec (Eichrom technologies) Matrix removal 0.1 M HNO3 Elution of Pb 0.05 M (NH4)2C2O4 Further sample preparation

Evaporation Take up residue in HNO3/H2O2 Evaporation Take up residue in HNO3/HF De Muynck et al, ABC, 390, 477486, 2008. PB ISOTOPIC ANALYSIS VIA MULTICOLLECTOR ICPMS PB INTOXICATION IN THE ROMAN ERA Contamination has to be avoided at all cost 3 < 10 particles / ft @ 0.5 m vs. millions particles / ft 3 Ultrapure water & acids PB ISOTOPIC ANALYSIS VIA MULTICOLLECTOR ICPMS PB INTOXICATION IN THE ROMAN ERA Isotope ratio precision Mass discrimination correction

208 206 Pb/ Pb 0.004 % RSD Tl as internal standard 207 206 Pb/ Pb 0.005 % RSD Russells equation - m R K true 1 R obs m 2 208 204 Pb/ Pb 0.02 % RSD 207 204

Pb/ Pb 0.02 % RSD 206 204 Pb/ Pb 0.02 % RSD Tl -2,00 Linear relation (Tl) - (Pb) -1,30 -1,95 -1,90 -1,85 -1,80 -1,75 -1,70

-1,65 -1,60 -1,55 -1,50 -1,40 -1,50 -1,60 y = 1,04222x + 0,17370 2 R = 0,99813 Pb -1,70 -1,80 -1,90 PB ISOTOPIC ANALYSIS VIA MULTICOLLECTOR ICPMS PB INTOXICATION IN THE ROMAN ERA 2.095 2.090

208 206 Pb/ Pb 2.085 2.080 2.075 bone tissue 2.070 2.065 2.060 2.055 0.830 207 206 Pb/ Pb 0.835

0.840 0.845 0.850 0.855 De Muynck et al, ABC, 390, 477486, 2008. PB ISOTOPIC ANALYSIS VIA MULTICOLLECTOR ICPMS PB INTOXICATION IN THE ROMAN ERA 2.095 208 206 Pb/ Pb 2.090 2.085 ? 2.080

2.075 2.070 bone tissue soil 2.065 2.060 207 206 Pb/ Pb 2.055 0.830 0.835 0.840

0.845 0.850 0.855 De Muynck et al, ABC, 390, 477486, 2008. 2.095 PB ISOTOPIC ANALYSIS VIA MULTICOLLECTOR ICPMS PB INTOXICATION IN THE ROMAN ERA 208 Pb/ 206 Pb 2.090 2.085 mixing line

2.080 2.075 2.070 2.065 bone tissue soil Pb artifacts 2.060 207 2.055 0.830

0.835 0.840 0.845 0.850 Pb/ 206 Pb 0.855 De Muynck et al, ABC, 390, 477486, 2008. PB ISOTOPIC ANALYSIS VIA MULTICOLLECTOR ICPMS PB INTOXICATION IN THE ROMAN ERA Pb objects & garum Bone tissue vs. soil: higher Pb concentration Isotope ratio shifted towards Pb objects, garum & amphorae Not only diagenesis pre-natal Intoxication Graveyard soils

amphorae De Muynck et al, ABC, 390, 477486, 2008. PROVENANCE DETERMINATION OF LEAD WHITE PIGMENT USED IN RENAISSANCE PAINTINGS P.P. Rubens 1577, Siegen (D) 1640, Antwerp (B) h th th Lead white (2PbCO3.Pb(OH)2) common white pigment in 16 -17 cent. paintings h Pb isotopic composition ~ provenance (geographical origin mining area) h 50 200 g sample suffices for MC-ICPMS Pb isotopic analysis PROVENANCE DETERMINATION OF LEAD WHITE PIGMENT

FORTUNATO ET AL., ANALYST, 130, 898-906, 2005. Rubens Rembrandt c Van Dyck 3-isotope plot Breughel PB ISOTOPIC COMPOSITION LEAD WHITE PIGMENTS VS. ORES FORTUNATO ET AL., ANALYST, 130, 898-906, 2005. 3-isotope plot h Pb ore, Pb isolated out of ore, pigment imported from England or Germany h Useful information in authentication studies & detection of overpaints a retouchings c

NATURAL VARIATION APPLICATIONS BASED ON ISOTOPE FRACTIONATION MC-ICPMS only B/10B ISOTOPIE RATIO DETERMINATION VIA ICP-QMS AS A TOOL FOR PROVENANCE DETERMINATION OF WINE 11 France Bergerac 3 wines 4.143 0.002 Swartland 8 wines 4.197 0.010 Italy Valpolicella 3 wines 4.125 0.002 Stellenbosch 5 wines 4.185 0.006 Robertson 4 wines 4.223 0.011

Coetzee and Vanhaecke, ABC, 383, 977-984, 2005. 11 10 B/ B AS A PALEO PH SEAWATER PROXY B in seawater: Present as B(OH)3 & B(OH)4- / distribution dependent on pH 11 B Concentration (mol/kg) sea water pH 11B/10B isotope ratio in the past? foraminifera & corals pH

11 10 B/ B AS A PALEO PH SEAWATER PROXY In seawater: + B(OH)3 + H2O B(OH)4 + H B(OH)4 taken up without isotopic fractionation isotopically isotopically heavier lighter in corals & foraminifera pH of seawater as a function(time)

Foraminifera living or fossil eukaryotic monocellular organisms with CaCO3 skeleton RELEVANCE OF PH OF SEAWATER ? Determined by CO2 concentration in the atmosphere CO2 H2CO3 Information on CO2 level over geological times Is the current increase in CO2 level exceptional ? RELEVANCE OF PH OF SEAWATER ? ? 11 B/

10 B DETERMINATION IN FORAMS FOSTER, EARTH PLANET. SCI. LETT., 271, 254, 2008 11 B/ 10 B determination ? Negative ion TIMS NTIMS Multi-collector ICP-MS MC-ICP-MS Sample preparation for MC-ICP-MS Crushing Removal of clay & organic material (NaClO) Dissolved in 0.5 M HNO3 Isolation of B using anion exchange chromatography

Amberlite IRA 743 MC-ICP-MS measurements MD correction via sample-standard bracketing Precision: 0.025% S ISOTOPIC ANALYSIS FOR TRACING DOWN COUNTERFEIT DRUGS R. CLOUGH ET AL., ANAL. CHEM., 78, 6126, 2006. Counterfeit drugs violation of intellectual property laws inappropriate quantities of active ingredients may contain ingredients that are not on the label (purity) often inaccurate, incorrect or fake packaging & labeling Money making drugs S ISOTOPIC ANALYSIS FOR TRACING DOWN COUNTERFEIT DRUGS

R. CLOUGH ET AL., ANAL. CHEM., 78, 6126, 2006. S isotopic analysis in viagra using LA-MC-ICP-MS Higher mass resolution EVALUATION OF THE LOCAL ENVIRONMENTAL IMPACT OF A PB-ZN SMELTER IN NORTHERN FRANCE Environmental effect of Pb-Zn smelter Traditional way = via Pb isotopic analysis 2.24 2 x standard error 2.22 European geogenic material 2.20

/ 206Pb Nord-Pas-de-Calais Broken Hill Leaded gasoline CH 2.18 2.16 208Pb Noyelles-Godault 2.14 Leaded gasoline EUR 2.12 2.10 1995 - 1996 snow

2.08 2.06 0.84 0.86 0.88 0.90 207Pb 0.92 0.94 0.96 / 206Pb Dring et al., Fresenius J Anal Chem, 1997, 359, 382-384 Complication?

Use of ores of varying provenance over the years Cloquet et al, ES&T, 49, 2525-2530, 2006. EVALUATION OF THE LOCAL ENVIRONMENTAL IMPACT OF A PB-ZN SMELTER IN NORTHERN FRANCE Alternative approach based on Cd isotopic analysis Cd By-product of Pb-Zn smelting Cd undergoes fractionation in smelting process Gas phase Gas phase enriched in isotopically lighter Cd Especially if gas phase is removed Cf. Instrumental fractionation in TIMS Liquid phase Cd isotopic analysis of topsoils (40 cm) Cloquet et al, ES&T, 49, 2525-2530, 2006. EVALUATION OF THE LOCAL ENVIRONMENTAL IMPACT

OF A PB-ZN SMELTER IN NORTHERN FRANCE Refinery slag ps To s oil ? Refinery dust Cloquet et al, ES&T, 49, 2525-2530, 2006. EVALUATION OF THE LOCAL ENVIRONMENTAL IMPACT OF A PB-ZN SMELTER IN NORTHERN FRANCE Refinery slag 3 sources: refinery dust, slag & agricultural practices Dust = most important contribution (> 60% for 65% of soils) Contribution from agriculture: max. 20-25%, often < 10% Refinery dust

Cloquet et al, ES&T, 49, 2525-2530, 2006. STUDY OF ISOTOPE FRACTIONATION IN THE CONTEXT OF BIOMEDICAL APPLICATIONS As Fe proceeds through the food chain, ( 56 54 Fe/ Fe) is reduced by approx 1 with each trophic level. Thorough investigation should provide information on uptake & transfer of Fe. Walczyk and von Blanckenburg, Science, 295, 2065- 2066, 2002. UPTAKE OF FE IN THE SMALL INTESTINE Fe isotopic analysis tool for efficiency of (non-heme) iron absorption Krayenbuehl et al, Blood, 105, 3812-3816, 2005. FE ISOTOPIC FRACTIONATION IN THE HUMAN BODY

STUDY OF HEMOCHROMATOSIS Unravelling the underlying mechanism of hereditary hemochromatosis Fe isotopic analysis tool for efficiency of (non-heme) iron absorption Indicator of disorder & means to test effect of therapies NATURAL VARIATION APPLICATIONS BASED ON EXTINCT RADIONUCLIDES MC-ICPMS only THE 182HF-182W CHRONOMETER S.B. JACOBSEN, EPSL, 33, 531-570 2005. c c Very short compared to age of solar system W isotopic analysis Extinct TIMS: hampered by hihgh IE(W) = 7,98 eV

radionuclide Straightforward with MC-ICP-MS THE 182HF-182W CHRONOMETER S.B. JACOBSEN, EPSL, 33, 531-570, 2005. Formation of a planet ? Accretion Growth of an object by attracting more matter (gravity) Differentiation Core formation Crust (light) Hf = lithophile prefers crust W = siderophile Iron core (heavy) prefers core THE 182HF-182W CHRONOMETER S.B. JACOBSEN, EPSL, 33, 531-570, 2005.

Effect of planetary differentiation? Situation 1: Hf & W only separated after extinction of 182 Hf Hf/W ratio ~ chondritic meteorites (unfractionated reservoir) Situation 2: Hf & W were separated while 182Hf was still around High Hf/W ratio in crust higher enrichment in 182W 182 Hf-182W chronometer Timing of planetary differentiation THE 182HF-182W CHRONOMETER S.B. JACOBSEN, EPSL, 33, 531-570, 2005. Increase in

182 W/ 183 In silicate fraction W THE END

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