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Mikael Axelsson Sales support specialist, Nordics

Trace Elemental, ICP-MS and Discrete Analyzers

87Rb/87Sr Interference Elimination using the Thermo Scientific iCAP TQ ICP-MS

NKS-B ICP User Seminar 2017

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There is No Application That Cannot be Tackled...Right?

Occupational health, e.g.

screening in blood Analysis of toxic elements

in products

Trace elements in Sea

Water

Trace elements in food

Elemental impurities in

drug products

Drinking water contaminants Environmental monitoring of

e.g. soils and waste

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ICP-MS Overview: Single Quadrupole ICP-MS

iCAP RQ ICP-MS

Innovative collision

cell

Bench-level easy-

access interface Compact footprint

Intuitive user-friendly

software

Simplified power

connections

Robust RF

generator

Quick connect and push-

fit sample intro

components

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Interferences – Spectral

Ar, Air (O, N, C)

H2O, Ca, Na, K, Mg, Cl

Reactants

• Spectral Interferences – ICP-MS • 2 most common types: isobaric and polyatomic

• Polyatomic Interferences • Produced when 2 or more isotopes combine to form a species with the same m/z as that of the analyte ion

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Interferences – Spectral

Spectral Interferences – ICP-MS • 2 most common types: isobaric and polyatomic

• Polyatomic Interferences • Produced when 2 or more isotopes combine to form a species with the same m/z as that of the analyte ion

Ar, Air (O, N, C)

H2O, Ca, Na, K, Mg, Cl

ArAr, ArO, ArN, ArC,

ArH, ArCa, ArNa, ArK,

ArMg, ArCl, ClO, NO,

CO, CaO, NaO, etc

Reactants Reaction Products

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• Polyatomic Interferences

Typical Interferenes - Examples

Element Interference How to remove

75As 40Ar35Cl+ KED

78,80Se 40Ar38Ar+; 40Ar40Ar+ KED, H2

51V 35Cl16O+ KED

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Handling Interferences – Kinetic Energy Discrimination

Target

Analyte 75As+

ArCl+,

Ca(OH)2H+

Quadrupole

isolates ions

wanted for

measurement

He KED filters out

unwanted

polyatomic

interferences, based

on difference in

cross-sectional size

of the analyte and

polyatomic

Complex

Matrix

Comprehensive

Interference

Removal

• He KED filters out unwanted

polyatomic interferences

• High transmission enables

analysis of even low mass

analytes in He KED mode

• Single measurement mode for

all analytes in analytical

method

KED = Kinetic Energy

Discrimination

Quadrupole set to filter

out exact mass of

target analyte

QCell in collision mode

with pure He uses

energy discrimination

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• Polyatomic Interferences

• Other Interferences – isobaric, doubly charged, high levels of polyatomics

Typical Interferenes - Examples

Isotope Interference How to remove

75As+ 150Sm2+, 59Co16O+ O2, mass shift of As

78,80Se+ 156, 160Gd2+ O2, mass shift of Se

111Cd+ 95Mo16O+ O2, H2, on mass

31P, 32S+ 14N16O1H+; 16O16O+ O2, mass shift of P, S

87Sr+ 87Rb+ O2, mass shift of Sr

Isotope Interference How to remove

75As+ 40Ar35Cl+ KED

78,80Se+ 40Ar38Ar+; 40Ar40Ar+ KED, H2

51V+ 35Cl16O+ KED

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ICP-MS Overview: Single and Triple Quadrupole ICP-MS

iCAP RQ ICP-MS

Innovative collision

cell

Bench-level easy-

access interface Compact footprint

Intuitive user-friendly

software

Simplified power

connections

Robust RF

generator

Quick connect and push-

fit sample intro

components

iCAP TQ ICP-MS

Reaction Finder

Software

Built-in safety for

handling reactive

gases

4 mass flow

controllers: He, O2,

H2, NH3

Additional quadrupole

for superior

interference removal

Analysis with SQ

and TQ in a single

sample run

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Thermo Scientific iCAP TQ ICP-MS – How it Works

Q1 rejects unwanted ions and

preselects the analyte. This first

stage of mass filtration rejects

precursors and ions with the same

m/z ratio as the product ion.

Optimal reaction conditions in Q2

are achieved through the selection

of the appropriate measurement

mode in Reaction Finder

Q3 isolates the product ion of the

analyte and removes any

remaining interferences through a

second stage of mass filtration

75As+

59Co+, 91Zr+

Q1 set to analyte

mass (m/z 75)

Q3 set to product ion

mass (m/z 91)

Q2 filled with reactive

gas (O2)

91[AsO]+

75As+ 91[AsO]+

59Co16O+, 150Sm++

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•

•

•

• TQ-ICP-MS offers multiple interference modes for

accurate analysis of your sample

• Problematic : when faced with measurement of a

sample where interferences expected, which is the

best measurement mode???

Taking the Complexity out of Triple Quad Technology

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1. Select Element/Isotope of interest

1. Reaction Finder proposes most

appropriate gas/scan setting

combination

3. Choose from list of Internal Standards

Solution is ‘Reaction Finder’ - method development assistant

Product ion

M+

Gas

Analyte

Result

Redefining triple quadrupole ICP-MS with unique ease of use

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Experimental Conditions: Thermo Scientific iCAP TQ ICP-MS

Parameter Value

Nebulizer MicroMist Quartz nebulizer 0.4mL·min-1, pumped at 40rpm

Spray chamber Quartz cyclonic spray chamber cooled at 2.7°C

Injector 2.5mm id, Quartz

Interface High Sensitivity (2.8mm) insert, Ni cones

RF Power 1550W

Nebulizer Gas Flow 1.11 L·min-1

QCell settings SQ-KED SQ-O2, TQ-O2 SQ-NH3, TQ-NH3

Gas Flow 100% He, 4.5 mL·min-1 100% O2, 0.35

mL·min-1

100% NH3, 0.33

mL·min-1

CR Bias -21 V - 7.5 V - 7.5 V

Q3 Bias -18 V -12 V -12 V

Scan Settings 0.1s dwell time per analyte, 30 sweeps, 10 main runs

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• Isobaric overlap between 87Rb and 87Sr leads to incorrect isotope ratio

determination

• Not resolved even using HR-ICP-MS (required resolution > 10,000)

Isobaric Interference Elimination 87Rb vs. 87Sr

Isotope Abundance [%]

85Rb 72.17

87Rb 27.84

Isotope Abundance [%]

84Sr 0.56

86Sr 9.86

87Sr 7.00

88Sr 82.58

!

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TQ-ICP-MS for isobaric interference removal

87Sr, 87Rb

All other interferences

e.g. 103Rh

87Rb

87Sr16O+

88Sr

All other interferences

e.g. 104Ru, 104Pd

88Sr16O+

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Detection Sensitivity 88Sr

Mode Sensitivity BEC IDL

SQ-KED 51,082 0.003 0.0002

TQ-O2 13,971 0.002 0.001

Relative sensitivity TQ-O2 vs. KED 27.3%

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Sample Isotope Ratio TQ-O2* Isotope Ratio SQ-KED*

10 µg·L-1 Sr 12.1175 ± 0.1447 [RSD 1.19%] 12.6280 ± 0.1097 [RSD 0.87%]

10 µg·L-1Sr, 10 µg·L-1 Rb 12.0635 ± 0.0877 [RSD 0.72%] 2.6572 ± 0.0122 [RSD 0.46%]

10 µg·L-1 Sr, 100 µg·L-1 Rb 12.1053 ± 0.1123 [RSD 0.93%] 0.3216 ± 0.0158 [RSD 4.90%]

10 µg·L-1Sr, 1 mg·L-1 Rb 12.1183 ± 0.1160 [RSD 0.96%] 0.0311 ± 0.0003 [RSD 0.91%]

10 µg·L-1 Sr, 10 mg·L-1Rb 12.0741 ± 0.0907 [RSD 0.75%] 0.0032 ± 0.00004 [RSD 1.10%]

10 µg·L-1Sr, 10 µg·L-1 Rb, 5 mg·L-1 Rh 12.00066 ± 0.1135 [RSD 0.95%] 2.6491 ± 0.0153 [RSD 0.58%]

10 µg·L-1Sr, 10 µg·L-1 Rb, 5 mg·L-1 Ru 12.1002 ± 0.0964 [RSD 0.80%] 2.6552 ± 0.0092 [RSD 0.35%]

• Isotope ratio in TQ-O2 is unaffected neither by increasing Rb

concentration nor presence of Rh or Ru

• Isotope ratio in SQ-KED is strongly affected by increasing Rb

concentration

• Attainable precision is not altered

Isotope Ratio Determination

* True value for 88Sr/87Sr is 11.7971. No correction for fractionation effects like mass bias has been applied

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• Measurement of Yb in a Gd matrix

• Same number of isotopes

• Similar abundances

• 16 mass units apart

iCAP TQ on mass measurement example

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• Calibration 0 – 5 ppb Yb in 10 ppm Gd – no gas

• Calibration 0 – 5 ppb Yb in 10 ppm Gd – KED

• NH3 reacts with many of the polyatomic ions that interfere with the REE

however NH3 also reacts quickly with some REE

• Pr, Eu, Dy, Ho, Er, Tm and Yb are less reactive with NH3

Yb in a Gd matrix

172Yb, no gas mode 172Yb, KED mode

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Yb measurement in 10pm Gd – TQ NH3 mode

• Sensitivity – 7100 cps/ppb

• BEC – 0.05 ppb

• IDL – 0.0001ppb

• Yb measured on mass at m/z 172

• NH3 flow – 0.9 ml/min

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• Non radiogenic isotope 204Pb used to correct for lead naturally occurring

in Pb/Pb dating

• 204Pb used as reference isotope for which others are compared

• Difficult to resolve these peaks even with HR-ICP-MS

Isotope ratio example - Pb in the presence of Hg and REE

Hg Isotopes Pb Isotopes

196Hg [0.14 %]

198Hg [10.02 %]

199Hg [16.84 %]

200Hg [23.13 %]

201Hg [13.22 %]

202Hg [29.80 %]

204Hg [6.85 %] 204Pb [1.40 %]

206Pb [24.10 %]

207Pb [22.10 %]

208Pb [52.40 %]

!

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Pb isotope ratio results with Hg added – SQ mode

Sample i.d 204Pb/208Pb

Theoretical ratio 0.02672

1ppb Pb 0.0258 ± 0.0001

1ppb Pb + 5ppb Hg 0.4301 ± 0.0025

1ppb Pb + 10ppb Hg 0.8941 ± 0.0055

1ppb Pb + 20ppb Hg 1.8270 ± 0.0051

• Measure isotope ratios in SQ mode

• Solutions with increasing Hg concentration

• Isotope ratio increases with increasing m/z 204 intensity

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• Hg reacts with NH3 in the QCell

• Pb is much less reactive: <1% of signal lost

• Remove 204Hg from 204Pb signal for accurate measurement

• Utilise TQ mode to eliminate any REE ammonia clusters that could form

and interfere with Pb; compare performance with SQ mode

• Eu(NH3)3, Yb(NH3)2, Ce(NH3)4

• 0.3 ml/min NH3 supplied into the QCell

• On mass measurement – both Q1 and Q3 set to transmit 204Pb

SQ and TQ mode with NH3 cell gas

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Isotope ratio with Hg and Yb added – SQ NH3 mode

Sample i.d. 204Pb/208Pb

Theoretical 0.02672

1ppb Pb 0.0258 ± 0.0001

1ppb Pb + 5ppb Hg 0.0258 ± 0.0001

1ppb Pb + 1ppm Yb 0.0721 ± 0.0002

• SQ mode using NH3 in the

QCell

• Hg reacts, so Pb interference

free at m/z 204

• However, Yb forms NH3 cluster

that SQ mode cannot resolve

Yb(NH3)2

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Sample i.d. 204Pb/208Pb

Theoretical 0.02671

1ppb Pb 0.02581 ± 0.0001

1ppb Pb + 5ppb Hg 0.02591 ± 0.0001

1ppb Pb + 10ppb Hg 0.02589 ± 0.0001

1ppb Pb + 20ppb Hg 0.02589 ± 0.0001

1ppb Pb + 1ppm Yb 0.02592 ± 0.0001

• Measurements repeated in TQ NH3 mode

• Again, Hg reacts with NH3, so Pb free from Hg interference at m/z 204

• Yb rejected by Q1 so cannot form NH3 cluster interference on m/z 204

• Accurate 204Pb/208Pb ratios obtained in TQ mode

Isotope ratio with Hg and Yb added – TQ NH3 mode

204Pb

Other interferences

e.g. 170Yb

204Pb

204Hg is eliminated

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• Triple quadrupole ICP-MS is a powerful tool for the removal of all kinds of

challenging interferences

• Rare earth doubly charged on As and Se not possible with single quad ICP-

MS

• Certain sample matrices may lead to very special overall interference

contributions, e.g. solutions containing high concentrations of metals Use of

reactive gases

• Isobaric interferences when isotope ratios need to be determined Leverage

different reactivity e.g. towards O2 as a reactive gas

• At the same time, a triple quadrupole instrument can be as easy to use as

a single quadrupole ICP-MS using modern control software

Summary and Conclusion

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• A big thanks to my colleges in Bremen and UK for producing the

data and these data will also soon be published, so stay tuned.