Exploring new fields of Applications using Multi Collector Magnetic Sector MS

Transcription

1 The world leader in serving science Exploring new fields of Applications using Multi Collector Magnetic Sector MS Sylveer Bergs Luca Simonotti Thermo Fisher Scientific Modena 28. & 29 Mai 2009

2 Introduction History HR ICP MS TIMS Isotopes Ion Sources Principles Detection Interferences Applications MC ICP MS 2

3 History 3

4 History TRITON NEPTUNE ELEMENT 2 4

5 Inductively Coupled Plasma Mass Spectrometry (ICPMS) Seminal work reported with ICP s as elemental MS ion sources First commercial quadrupole ICPMS instruments become available 1985 Laser ablation first used with ICPMS for direct solids sampling Alternate-gas plasmas investigated 1989 First sector-field, high-resolution ICPMS instrument described 1992 Multi-collector, sector-field ICPMS instrumentation debuts Novel ICPMS designs (ITMS, ToF-MS, FTICR-MS) investigated Low-power, cool plasmas techniques described for interference reduction Collision/reaction cell ICPMS techniques described/commercialized 2002-present Applications developments: metallomic, elemental imaging, radioisotopes, high precision isotope ratios, fs-lasers etc. 5

6 What are Isotopes? Isotopes: from the Greek iso-,meaning equal, and topos, meaning place ; referring to their same position in the periodic table. What are isotopes? Isotopes of an element have the same atomic number but a different number of neutrons, and thus different atomic weights. Isotope Protons Neutrons Total Abundance 16 O % 17 O % 18 O % 6

7 Types of isotopic systems Radioactive: naturally unstable isotopes that spontaneously disintegrate or decay to form new isotopes or elements. e.g. 87 Rb 86 Sr e.g. 238 U 234 Th 234 Pa 234 U Pb In geology and archaeology, radioactive isotopes are commonly used to determine age. Stable: Naturally stable - so, don t spontaneously disintegrate or decay. e.g. Oxygen ( 16 O, 17 O, 18 O), Carbon ( 12 C, 13 C, 14 C) Stable Isotope Mass Spectrometer (Delta series, MAT253) ALSO: Lithium ( 6 Li, 7 Li), Sulfur ( 32 S, 33 S, 34 S, 36 S), Iron ( 54 Fe, 56 Fe, 57 Fe, 58 Fe) Multi Collector Mass Spectrometer 7

8 Isotopic fractionation The partitioning of isotopes between two substances or two phases Why are isotopes so useful? Fractionation effects can be related to various biological, geochemical, geological processes. 8

9 Measuring Isotopes -Most of the isotopic variations are subtle but significant -Measuring absolute isotope abundances is very difficult -The isotopic ratio is always measured with respect to a reference material (a standard) 9

10 Notation In isotope geochemistry it is common practice to express the isotopic composition in terms of delta ( ) values. Rsample = - 1 x 1000 Rstandard Rsample = heavy isotope/light isotope in the sample Rstandard = heavy isotope/light isotope in the standard 10

11 Use of Stable Isotopes Li, B, Mg, Si, S, Ca, Fe, Cu, Zn... Used in geology, geochemistry, biology... to study biochemical processes in humans, animals and plants... to study planetary evolution... to study mantle convection and recycling processes on Earth... to study ocean temperature changes throughout the Earth s history 11

12 Mass Spectrometry 1.Ion source: The part of the instrument where ions are formed, accelerated and focused into a narrow beam. 2. Electric sector: Focuses the ions on energy according to: 1/2Mv 2 = ev 3. Magnet: Separates the ion beams according to their mass/charge ratio (m/z). Light ions are more deflected than heavier ions. 4. Detector system: The separated ions are collected in a detector, converted into an electrical pulse and amplified. 12

13 Ion Sources: TIMS vs. (MC-)ICPMS Thermal Ionization (TI) Ionization takes place by contact with the heated surface of a metal filament... Small energy spread Inductively Coupled Plasma (ICP) Ionization takes place in an Ar plasma (partly ionized gas generated by RF magnetic fields)... Larger energy spread (Shielded Torch) 13

14 Principle of Magnetic Sector Mass Spectrometry MAGNET heavy masses Ionization Source light masses Detectors 14

15 Working principle of a magnetic sector field mass analyzer Lorentz force: F=q(E+v x B) r=(m*v)/(e*b) 15

16 Multicollection vs. Single collection magnet magnet heavier heavier Ion source lighter Ion source lighter Multicollection Detectors can be 3 (or more) detectors Faraday collectors (least sensitive) Analog SEMs Counting SEMs (most sensitive) Or any mixture of above 1 detector Single collection 16

17 Why sector field mass analyzers for isotope ratio measurements? Unique features of magnetic sector field mass analyzers: High acceleration voltages give high transmission High sensitivity Ions with different mass are separated in space Ability for parallel detection Ability for high mass resolution Elimination of interferences 17

18 Intensity Sequential measurement of isotope intensities IR = I isotope1 (t)/i isotope2 (t) Isotope 2 Isotope 1 time Precision and accuracy depend on signal stability 18

19 Intensity Parallel measurement of isotope intensities IR = I isotope1 (t)/i isotope2 (t) Isotope 2 Isotope 1 time High precision isotope ratio measurements require parallel detection of all isotopes to eliminate ion source fluctuations Precision and accuracy independent on signal stability 19

20 To remember: Multicollection vs. Single collection Multicollection: All isotopes of interest are measured simultaneously Highest sensitivity (100% duty cycle) Fluctuations in signal intensity have no effect on isotope ratios Need of detector cross calibration for accuracy Single collection: One isotope is measured at any time No detector cross calibration error Lower sensitivity (duty cycle < 100%) Measured isotope ratio sensitive to signal fluctuation 20

21 To remember: Sector Field Mass Spectrometer A magnetic sector mass spectrometer is the ideal mass analyzer for high precision isotope ratio measurements: High transmission Spatial separation of ions along the focal plane: parallel detection Ability for high mass resolution Angular focusing: Ions emerging from the same spot (entrance slit) but different angles are focused onto the same spot in the image plane of the analyzer. Energy focusing: Ions starting from the same spot and the same angle but different ion energies are focused onto the same spot in the image plane of the analyzer. Double focusing: a combination of a magnetic sector field and an electrostatic sector field can achieve angular focusing and energy focusing at the same time. For TIMS a single focusing sector field is sufficient because of the small energy spread of the ions: angular focusing. ICP-MS needs double focusing analyzers because of large energy spread: angular and energy focusing. 21

22 Detection Laminated magnet Focus quad Zoom lens Source lens stack Collector array 21 sample turret RPQ-SEM Optical magnification of M = 2 Larger layout of the Instrument Improved Faraday Cup performance (twice as wide) Mass dispersion 818mm 22

23 Detection: Classical approach Source Faraday Cup Magnet lens M=1 Traditional Ion Optics Secondary particles are released close to cup entrance. 23

24 Effect of large magnification ion optics Source Magnet lens M=1 Faraday Cup Secondary particles are released close to cup entrance. 81 cm mass dispersion; M=2 Faraday Cup Source Magnet lens TRITON Larger effective depth of cups! Less emission of secondaries! 24

25 Effect of larger ion optical magnification Larger distance of adjacent masses Wider detectors: more space Reduced angular divergence More effective Faraday Cups 25

26 Variable Multicollector Variable in position Variable in detector type (Faraday/MIC) Precise positioning (<10 m) by insitu position readout 17 % relative mass range 26

27 Multi-Collector Top View Amplifier RPQ / Ion Counter Ions 27

28 High abundance sensitivity: RPQ filter lens Ion Beam RPQ Energy Filter Faraday Ion Counting Acts as an energy filter to discriminate against Ions that have lost some energy due to scattering events 28

29 How to deal with interferences? Example 4: Interference of 238 U + tailing on 236 U U + tailing from 238 U + 29

30 Abundance Sensitivity No RPQ: ABS 5.8 ppm 30

31 Abundance Sensitivity Watch the scala! With RPQ: ABS < 1 ppm 31

32 MC-ICPMS: NEPTUNE double focusing magnetic sector Laminated magnet Zoom lens Collector array ESA D 2D RPQ-SEM Slit Transfer lens 812 mm mass dispersion ICP source at ground 32

33 Gain Calibration Common to all MC systems is the need for cross calibration. Classical Method of cross calibration a high precision, constant current source is sequentially connected to all amplifiers precision of gain calibration, the reproducibility of the electronic cross calibration of the amplifier gain is about 5 ppm/channel Consequence for a two-isotope system Resulting uncertainty for the external reproducibility can never be better then: 2 2 = (5 ppm) + (5ppm) 7ppm 33

34 The virtual amplifier concept We introduce a relay matrix between the Faraday Cups and the current amplifiers: flexibility to switch the amplifiers between different Faraday cups. The amplifiers are switched between measurement blocks so that in the end all amplifiers have been connected to all Faraday cups All signals have been virtually measured with the same set of amplifiers: Gain uncertainty cancels for isotope ratios 34

35 Virtual Amplifier Concept relay closed relay open Amplifier and V/F converter Front end processor Up to 10 current amplifiers with different gains (10 10 Ω, Ω, Ω) can be installed simultaneously. A relay matrix connects the amplifier array to the Faraday Cup array. The connection scheme is controlled by the software. This enables the user to choose the amplifier configuration needed for the current analytical task and required precision. Evacuated and thermostated housing 35

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46 TIMS - TRITON Nd isotopes Breaking the 5ppm barrier 46

47 Detector System Faraday Cup Detectors Robust Large Dynamic Range Long lifetime Multi Ion Counting Very sensitive Low Noise Low Detection Limit 47

48 Extending the dynamic range up to 500 V up to 500V up to 50 V up to 5 V up to 1,000k cps up to 200k cps 1mV to 50mV 50mV to 50V (Multi) Ion Counting Ohm Ohm Ohm Detector Type and Amplification 48

49 10 12 Ohm Resistors vs Ohm The larger resistor results in a 10 times higher gain of the amplifiers (relative to Ohm), but at the same time the noise of the resistor only increases by 10. Signal-to-noise improves by factor 2-3 i.e. 10 / 10 Precision for low signals (<50mV) improved Sub permil for 1mV signals 49

50 Extending the dynamic range of Faraday Cup measurements Three choices of amplifiers: Ohm feedback resistors Dynamic range up to 50V Low Noise Ohm feedback resistors Dynamic range up to 500V Ohm feedback resistors Dynamic range up to 5V Reduced noise level! Fully automated control by software 50

51 Cup L3 Cup L2 Cup L1 Centre Cup H1 TIMS: Nd measurements using Ohm Method: A Merck Neodymium sample was measured at six different 144 Nd intensities, ranging from 50 mv down to 1.5 mv Ohm Ohm Ohm Ohm Ohm #9 #6 #7 #2 #8 Faraday Faraday Faraday Faraday Faraday 142 Nd 143 Nd 144 Nd 145 Nd 146 Nd 51

52 Results Nd/ 144 Nd/ 144 Nd Nd Log(Intensity 144 Nd (mv)) Log(Intensity 144 Nd (mv)) Ohm Ohm 3mV ( 144 Nd): SE = 0.35 permil 3mV ( 144 Nd): SE = 1.1 permil 52

53 Implementation of Resistor 53

54 Detector System Faraday Cup Detectors Robust Large Dynamic Range Long lifetime Multi Ion Counting Very sensitive Low Noise Low Detection Limit 54

55 Why Multi Ion Counting (MIC)? 1 mv Faraday signal ca. 60,000 cps on IC signal/noise 55

56 Multicollector with Multi Ion Counting 1 MIC 4 MICs plug-in MIC detectors identical in size and interchangeable with Faraday cups up to 8 MIC channels plus 9 Faraday cups can be installed simultaneously 56

57 MC-ICPMS: Interferences Isobaric elemental interferences 146 Sm + interference on 146 Nd + Detect 147 Sm + Isobaric doubly- (or multiply-) charged ions 86Sr ++ interference on 43Ca + Detect mass 43.3 ( 87 Sr ++ ) Isobaric molecular (poly-atomic) 40 Ar 16 O interference on 56 Fe High mass Resolution 57

58 How to deal with interferences? Low resolution ( normal mode) High resolution (narrow slits) 56 Fe 40 Ar 16 O 40 Ar 16 O 56 Fe

59 NEPTUNE: Mass Separation by HR 56 Fe + 40 Ar 16 O 56 Fe High resolution entrance slit Low resolution exit slit 40 Ar 16 O

60 signal (V) normalised to 56Fe Peakscan of Fe (wet plasma, 1 ppm, medium resolution slit) Fe (L2) 56 Fe (C) 57 Fe (H1) 58 Fe (H2) Fe + Interferences Ar 16 O 40 Ar 16 OH 40 Ar 18 O 40 Ar 14 N mass 56Fe 40Ar16O Collector slit Faraday cup 60

61 signal (V) normalised to 56Fe Peakscan of Fe (wet plasma, 1 ppm, medium resolution slit) Fe (L2) 56 Fe (C) 57 Fe (H1) 58 Fe (H2) Fe + Interferences Ar 16 O 40 Ar 16 OH 40 Ar 18 O 40 Ar 14 N mass 56Fe 40Ar16O Collector slit Faraday cup 61

62 signal (V) normalised to 56Fe Peakscan of Fe (wet plasma, 1 ppm, medium resolution slit) Fe (L2) 56 Fe (C) 57 Fe (H1) 58 Fe (H2) Fe + Interferences Ar 16 O 40 Ar 16 OH 40 Ar 18 O 40 Ar 14 N mass 56Fe 40Ar16O Collector slit Faraday cup 62

63 Fe isotope fractionation along food chain Potential use of Fe isotopes in environmental geosciences: - Study Fe redox cycle - Trace microbial activity - Study Fe metabolism in humans Fractionation effects in higher organisms Walczyk and von Blanckenburg (2005) Int. Journal of Mass Spectrometry V242,

64 Fe isotope fractionation in lunar samples Earth s mantle The isotopically heavier Fe isotope composition of lunar samples probably reflects fractionation during the differentiation history of the Moon. Figure from Weyer et al (2005) EPSL V240,

65 Applications 65

66 Pb isotope ratios using Multi-Ion-Counting Multi Ion Counting on the NEPTUNE 66

67 Multi Ion Counting NEPTUNE: Pb isotope ratios Pb isotope ratios External normalisation using sample-standard-bracketing Multi Ion Counting 202Hg 204Pb(+Hg) 206Pb 207Pb 208Pb Environmental Samples (rainwater, groundwater, river water) Low Pb concentrations, down to 100pg/g = 100ppt 67

68 Multi Ion Counting NEPTUNE: Pb isotope ratios External Reproducibility for 207 Pb/ 206 Pb is <0.15% (2SD) Cocherie and Robert (2007) Chemical Geology, p

69 U-Pb dating of zircons using Laser & Multi-Ion-Counting 69

70 Geological clock Uranium 238 U Lead 206 Pb Quantity 70

71 How old is our Planet?? Lead-Isotopes Result: 4,55 Billion years 71

72 Multi Ion Counting NEPTUNE: U-Pb dating of zircons IC IC L4 IC IC IC H3 IC H4 IC 202Hg 204Pb+Hg - 206Pb 207Pb 208Pb 232Th 238U 202Hg 204Pb+Hg - 206Pb 207Pb 208Pb 232Th 238U Laser Ablation in combination with MIC Pb-U isotope ratios External normalisation using sample-standard-bracketing Zircons Spot size: 20μm 72

73 Typical Application MIC: dating zircons IC5 IC4 Cup L4 IC3 Cup L3 IC2 Cup L2 Cup L1 Center Cup H1 Cup H2 Cup H3 IC6 Cup H4 IC6 202 Hg Pb 207 Pb 232 Th 238 U Ion Ion Ion Ion Ion Ion Counter Counter Counter Counter Counter Counter Faraday Faraday Faraday Faraday Faraday Faraday Faraday Faraday Faraday 73

74 Multi Ion Counting NEPTUNE: U-Pb dating of zircons Precision for 207Pb/206Pb is <1 % (2sigma) 74

75 Zircons: Measurement and evaluation strategy L4-detector platform H4 detector platform IC2 IC3 IC4 IC6 FAR FAR IC7 202Hg 204(Hg+Pb) 206Pb 207Pb 208Pb 238U Simultaneous measurement of 202 Hg, Pb and 238 U 213 nm spots Sample/standard approach Ca. 90s/spot IC2: 207 Pb IC3: 206 Pb IC4: 204 Pb+ 204 Hg IC5: 202 Hg IC6: 238 U 75

76 Comparison with TIMS Laser Ablation NEPTUNE using MICs TIMS 76

77 S isotopes Why S? To detect counterfeit pharmaceutical products, e.g., Pfizer Viagra. 77

78 S isotope analysis by other techniques Traditionally S isotopes are measured by GIRMS. Precisions: down to 0.05 permil possible Disadvantage: complex experimental setup Fluorination of S is necessary, so lots of safety precautions Disadvantage: no in-situ analysis possible 78

79 S isotope analysis on the NEPTUNE S isotope analysis by NEPTUNE: High Mass Resolution Laser Ablation Precision: ~0.4 permil 34 S relative to Pfizer Viagra) Counterfeit Viagra 1 Genuine Pfizer Counterfeit Viagra Viagra 2 plus C N Figure provided by LGC, UK. Article: Clough et al. (2006) Analytical Chemistry 79

80 Cl isotopes Gas Chromatography coupled to the NEPTUNE 80

81 Cl isotopes Why Cl? To characterize CAHs (chlorinated aliphatic hydrocarbons). These have been extensively used in many industries since the 1940s. CAHs are widespread groundwater pollutants, where they can remain for long periods of time. Trichlorethene (TCE) and perchloroethylene (PCE) have been used as degreasing solutions in industry since

82 Cl isotope analysis on the NEPTUNE Cl isotope analysis by NEPTUNE: High Mass Resolution Gas Chromatography! Precision: down to 0.12 permil (2RSD) Article: Van Acker (2006) Analytical Chemistry Figure taken from Van Acker et al. (2006). 82

83 Cl isotopes by other techniques Traditionally Cl isotopes are measured by GIRMS. Precisions: down to 0.08 permil Disadvantage: conversion and purification steps High costs Disadvantage: low sensitivity GIRMS: Minimum sample size is ~140µg of chlorine. or TIMS Disadvantage: see above, and low precision: 0.3 permil 83

84 CAHs: Comparison of GC-MC-ICPMS with previous methods Complexity of sample preparation and analysis time have been reduced significantly: Batch of 8 samples needs about 12 days with the previous methods 2 hours with GC-MC-ICPMS method! Sample amounts: µg Reproducibilty of GIRMS is best (0.08 ), but GC-MC-ICPMS yields similar precisions as TIMS (ca. 0.3 ). GC-MC-ICPMS is potentially a fast screening method for envrionmental samples: analysis of complex mixtures of CAHs. 84

85 Br isotopes Gas Chromatography coupled to the NEPTUNE 85

86 Br isotopes Why Br? Bromomethane (CH 3 Br) is a major reactant for destroying the stratospheric ozone layer Naturally produced: emitted during biomass burning biosynthezised by marine algae > 1600 brominated organic compounds Anthropogenic sources Flame retardants Pesticides Some of them appear in human breast milk Detected in marine food tissues Concentrations in human blood is rising Can we distinguish between between natural and industrial sources? 86

87 Br isotopes analysis on the NEPTUNE using GC Br isotope analysis by NEPTUNE: Gas Chromatography Precision: <0.3 permil Sample size: 0.3 nmol 87

88 Thank you for your attention Questions 88