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Fergus Keenan Shona McSheehy Julian Wills

Novel QCell Technology for Inference Removal in ICP-MS - Combining Low Mass Filtration with Kinetic Energy Discrimination

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Outline

• Characteristics of ICP-MS • Overview of the Thermo

Scientific™ QCell • Simple and generic setup using

Autotuning • Helium KED mode for single

mode interference removal • Reactive interference removal • Helium Collisional Focusing

applicatons • Summary

Thermo Scientific™ iCAP™ Q ICP-MS

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ICP-MS is an Omnivore

• It can measure almost the whole periodic table in just about everything • It is not limited to elemental concentrations but offers high precision

isotope ratio determinations and, if coupled to separation devices, species information

• The challenge for today’s users of ICP-MS is to maintain its multi-elemental capabilities during the analysis of a large variety of samples at low concentration levels with high throughput and the highest data quality

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ICP-OES: • Light emitted by excited atoms in

the ICP is measured at wavelengths (λM) specific to the element of interest

• Complicated spectra

Characteristics of ICPs

• ICPs have the following advantages for both ICP-OES and ICP-MS: • High efficiency ion source:

• High sensitivity • Wide elemental coverage • High matrix tolerance

• Atmospheric ion source – high flexibility for coupling of sampling devices

ICP-MS: • Ions (M+) generated in the ICP

are extracted and sorted by mass • Relatively simple spectra • Isotopic information

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ICP-OES:

Characteristics of ICPs

• ICPs have the following advantages for both ICP-OES and ICP-MS: • High efficiency ion source:

• High sensitivity • Wide elemental coverage • High matrix tolerance

• Atmospheric ion source – high flexibility for coupling of sampling devices

ICP-MS:

Both spectra of 10ppb V

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The Problem at Hand

• There are two fundamental limitations of the ICP-MS technique: • Interferences generated from both background and sample

matrix ions can limit the measurable concentration range in many sample types

• The ICP-MS interface limits sample throughput: • The absolute content of the matrix (usually kept < 0.2 %) • The duration that a sample matrix can be analyzed

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The QCell

• Proprietary design • 4 Flatapoles • Automatic low mass cut-off

• Zero-maintenance, Non-consumable

• 50% smaller volume for faster mode switching (<10s)

• Single mode interference removal with He for routine applications

• High ion transmission for improved sensitivity when using kinetic energy discrimination

• Can also use reactive mode with O2, H2 or NH3 mixes

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Stability diagram of quadrupole (≈flatapole)

• QCell operates in RF only mode • Only the q value (x-axis) changes

with RF amplitude V, not a (y-axis) at given frequency f

• Well-defined stability boundaries in contrast to higher order multipoles

• Interference that are created by reactions of lower masses in the cell can be significantly reduced

• Example:

• At q = 0.8 for a particular mass m e.g. 24 we are within the stable region (blue line in diagram).

• Smaller masses have a higher q value and thus are no longer in the stable region e.g. mass 14 (see insert)

Stability region

Lower mass

2 20

2rfmVeq

⋅⋅⋅

=

q

a

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QCell – Low Mass Cut-Off KED mode

Measuring 56Fe

QCell Mass Cut-Off Region (here all masses below 39)

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2

3

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QCell: Effect of Low Mass Cut-Off on in-cell Interference Formation

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Automated QCell Optimization for CCT Mode

• Optimum CCT gas flow obtained using the default CCT Autotune • Generic autotune procedure • Independent of the nature of

the gas used • He, O2, H2/He etc.

• Easy and effective way to

configure the CCT settings

• He

• 100 % O2

Parameter Value

Gas flow 7.2 ml min-1

QCell bias - 8 V

Quad bias - 12 V

Parameter Value

Gas flow 0.4 ml min-1

QCell bias - 6 V

Quad bias - 12 V

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QCell: Faster Gas Switching

• 5 repeats of STD-KED Mode Switch

• Results: • ~5 s for STD to KED switch

• He gas flow from 0 to ~5 ml/min • Voltage changes are

instantaneous • N.B. Low signal from 0 – 1 s is

wait before KED gas starts

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QCell: A Non Consumable Item

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QCell KED – Single Mode Interference Suppression

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5% HNO3 Blank 5% HNO3 Blank +10ppb Spike

QCell KED – Single Mode Interference Suppression

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5% HNO3 5% HCL 1% IPA 1% H2SO4

Blank

5% HNO3 5% HCL 1% IPA 1% H2SO4

+10ppb Spike

QCell KED – Single Mode Interference Suppression

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5% HNO3 5% HCL 1% IPA 1% H2SO4 200ppm Na 500ppm P 200ppm Ca

Blank

5% HNO3 5% HCL 1% IPA 1% H2SO4 200ppm Na 500ppm P 200ppm Ca

+10ppb Spike

QCell KED – Single Mode Interference Suppression

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QCell KED – Even More Effective KED

• CeO+/Ce+ Ratio = 0.02%

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QCell KED – Even More Effective KED

5% HNO3 5% HCL 1% IPA 1% H2SO4 200ppm Na 500ppm P 200ppm Ca

Blank

5% HNO3 5% HCL 1% IPA 1% H2SO4 200ppm Na 500ppm P 200ppm Ca

+10ppb Spike

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5% HNO3 5% HCL 1% IPA 1% H2SO4 200ppm Na 500ppm P 200ppm Ca

Blank

5% HNO3 5% HCL 1% IPA 1% H2SO4 200ppm Na 500ppm P 200ppm Ca

+10ppb Spike

QCell KED – Single Mode Interference Suppression

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QCell KED: Calibration Lines

2.5% HNO3 / 1.5% HCl

51V KED: BEC: 12ppt, LoD: 7ppt

75As KED: BEC: 17ppt, LoD: 5ppt

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QCell KED: Calibration Lines

100% Low Boiling Point Naphtha

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QCell: Full Mass Range KED Analysis

All single He KED mode

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iCAP Qc ICP-MS for Clinical: Analysis of *20 Diluted Urine

0%

20%

40%

60%

80%

100%

120%

140%

160%

180%

200%

Accu

racy

(%)

UTAK Urine

normal Verified Value

Expected Value

51V 0.05 0.06 0.05-0.07 52Cr 0.13 0.12 0.1-0.14 55Mn 0.29 0.29 0.25-0.33 59Co 0.14 0.17 0.14-0.2 60Ni 0.38 0.36 0.31-0.41 65Cu 11.5 11.8 10-13.6 66Zn 83.5 78.3 66.6-90.0 75As 1.1 0.95 0.8-1.1 78Se 5.4 5.6 4.8-6.4 98Mo 7.9 7.1 6-8.2 208Pb 0.06 0.06 0.05-0.07

All single He KED mode

Accuracy for UTAK Normal Urine control: Approximate adult normal range

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Reactive Chemistry with the QCell

• Problem: • Parent ions form oxide

polyatomic interferences that interfere with target isotopes

• Example: • Determination of Cd in the

presence of Mo (e.g. in waste waters) is limited due to the formation of 95MoO & 98MoO at 111Cd & 114Cd

• Solution: • Introduce a reactive gas into the

QC • ‘Mass Shift’ the interference

away from the target isotope

• Example: • Add O2 into the QCell, moving

MoO to MoOx

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iCAP Q ICP-MS: O2 QCell – 1ppm Mo

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iCAP Q ICP-MS: O2 QCell – 1ppm Mo + 5ppb Cd

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iCAP Q ICP-MS: O2 QCell

1ppm Mo 1ppm Mo + 5ppb Cd

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Measurement of Iodine 129

• Radioactive nuclides of Iodine need to be monitored • 129I, t ½ 15.7 million years, β-decay • 131I, t ½ 8d, γ-decay

• Ar gas used for plasma generation may contain Xe impurities

• 129Xe, 131Xe create background signal

• Isobaric interference Not removeable with KED

• Use of 100% O2 to generate XeO!

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Effect of QCell Conditions

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1

10

100

1000

10000

100000

1000000

0 0.2 0.4 0.6 0.8 1

129I

BEC

(ppt

)

Sign

al In

tens

ity

Oxygen CCT Gas Flow (ml/min)

10ppb 127I (cps) 129I Background (cps) 129I BEC (ppt)

• Optimum O2 CCT gas flow obtained using the default CCT Autotune!

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Performance of the Different Measurement Modes

127I (cps) 129Xe (cps)

Blank 400 200

10 ppb Iodine 493,763 400

LOD: 0.08 ng kg-1

BEC: 0.95 ng kg-1

127I 129Xe

127I (cps) 129Xe (cps)

Blank 1,017 2,498

10 ppb Iodine 528,810 2,473

LOD: 6.9 ng kg-1

BEC: 50.9 ng kg-1

127I 129Xe

127I (cps) 129Xe (cps)

Blank 200 221

10 ppb Iodine 49,264 267

LOD: 49.3 ng kg-1

BEC: 46.7 ng kg-1

127I 129Xe

• STD mode: Isobaric Interference clearly visible • KED mode: Iodine Sensitivity drops • CCT mode: No background from Xe, sensitivity comparable to STD mode

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Sensitivity Improvement using He in the QCell

• Collisional focusing = Reduction of natural dispersion of the ion beam in the cell due to collisions with He atoms

• Effect is especially pronounced for ions with m/z ≥ 100! • Gain in sensitivity of a factor 2-3!

“Collisional focusing doesn't get you any "new" ions, it just gives you back some of the ions which were lost by ion beam expansion in the unpressurized cell”

Cited from Ed McCurdy, (PlasmaChem archive, item 018123) (http://listserv.syr.edu/scripts/wa.exe?S1=plasmachem-l)

Element Sensitivity [cps ppb-1] STD mode*

Sensitivity [cps ppb-1] KED mode*

Sensitivity [cps ppb-1] CCT mode*

Factor CCT/STD mode

7Li 93,533 373 9,186 0.1 59Co 118,329 41,265 132,526 1.1 115In 255,203 72,485 414,063 1.6

140Ce 258,760 177,487 483,867 1.87 238U 392,218 488,379 1,277,818 3.25

* Performance of a typical iCAP Qc model

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QCell: Collisional Focusing Performance

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QCell: Collisional Focusing Performance

• Collision focusing with pure He on the iCAP Q can give up to a 3 fold improvement in sensitivity.

• For higher masses, ion energies are lower (due to the increased # of collisions) and they therefore the have a longer residence time in the QCell and thus the RF can focus them better, leading to improved transmission & sensitivity

STD Spec (kcps/ppb)

CCT (kcps/ppb)

Factor (CCT/STD)

59Co 200 310 1.5 115In 400 786 2.0 238U 500 1500 3.0

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QCell: Collisional Focusing Performance

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QCell: Collisional Focusing Performance

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iCAP Qc ICP-MS: Collisional Focusing Isotope Ratios

• iCAP Qs • He CCT Mode • Self-aspiration • 1ppb NBS SRM U010

• 1.9 Mcps/ppb U • 10 * 1 min analyses

• <0.1% RSD • <1% accuracy

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iCAP Qc ICP-MS: Collision Focusing Lowers Abundance Sensitivity

• 10ppm U Standard: • He CCT Mode • Optimized pole bias

• 237/238: • 57/3,579,950,807 • 1.6*10-8 / 0.016 ppm • *30 better than standard

specification • 239/238(UH+ formation, non

desolvation): 29ppm

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Summary and Outlook

The QCell of the iCAP Q ICP-MS offers great versatility for a variety of challenging applications:

Powerful interference removal through He KED Sensitivity Improvement by factor 3 for heavy elements Removal of isobaric interferences after conversion into oxides Effective reaction chemistry for mass shifting to less interfered regions Collisional Focusing enhances Isotope Ratio measurements & Abundance Sensitivity

The sophisticated autotune procedures automatically adjust the gas flows and lens voltages independently of the applied CCT gas

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Thank you for your attention!