Fergus Keenan Shona McSheehy Julian Wills

Transcription

1 Novel QCell Technology for Inference Removal in ICP-MS - Combining Low Mass Filtration with Kinetic Energy Discrimination Fergus Keenan Shona McSheehy Julian Wills 1 The world leader in serving science

2 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 2

3 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 multielemental capabilities during the analysis of a large variety of samples at low concentration levels with high throughput and the highest data quality 3

4 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-OES: Light emitted by excited atoms in the ICP is measured at wavelengths (λ M ) specific to the element of interest Complicated spectra ICP-MS: Ions (M + ) generated in the ICP are extracted and sorted by mass Relatively simple spectra Isotopic information 4

5 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-OES: ICP-MS: 5 Both spectra of 10ppb V

6 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 6

7 The QCell Proprietary design 4 Flatapoles Automatic low mass cut-off Zero-maintenance, Nonconsumable 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 O 2, H 2 or NH 3 mixes 7

8 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 a Stability region Example: At q = 0.8 for a particular mass m e.g. 24 we are within the stable region (blue line in diagram). q Lower mass Smaller masses have a higher q value and thus are no longer in the stable region e.g. mass 14 (see insert) q = 2 e V m f 2 r 2 0 8

9 QCell Low Mass Cut-Off KED mode QCell Mass Cut-Off Region (here all masses below 39) Measuring 56 Fe 9

10 QCell: Effect of Low Mass Cut-Off on in-cell Interference Formation 10

11 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, O 2, H 2 /He etc. Easy and effective way to configure the CCT settings He 100 % O 2 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 11

12 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 12

13 QCell: A Non Consumable Item 13

14 QCell KED Single Mode Interference Suppression 14

15 QCell KED Single Mode Interference Suppression 5% HNO3 Blank 5% HNO3 Blank +10ppb Spike 15

16 QCell KED Single Mode Interference Suppression 5% HNO3 5% HCL 1% IPA 1% H2SO4 Blank 5% HNO3 5% HCL 1% IPA 1% H2SO4 +10ppb Spike 16

17 QCell KED Single Mode Interference Suppression 5% HNO 3 5% HCL 1% IPA 1% H 2 SO 4 200ppm Na 500ppm P 200ppm Ca Blank 5% HNO 3 5% HCL 1% IPA 1% H 2 SO 4 200ppm Na 500ppm P 200ppm Ca +10ppb Spike 17

18 QCell KED Even More Effective KED CeO + /Ce + Ratio = 0.02% 18

19 QCell KED Even More Effective KED 5% HNO 3 5% HCL 1% IPA 1% H 2 SO 4 200ppm Na 500ppm P 200ppm Ca Blank 5% HNO 3 5% HCL 1% IPA 1% H 2 SO 4 200ppm Na 500ppm P 200ppm Ca +10ppb Spike 19

20 QCell KED Single Mode Interference Suppression 5% HNO 3 5% HCL 1% IPA 1% H 2 SO 4 200ppm Na 500ppm P 200ppm Ca Blank 5% HNO 3 5% HCL 1% IPA 1% H 2 SO 4 200ppm Na 500ppm P 200ppm Ca +10ppb Spike 20

21 QCell KED: Calibration Lines 51 V KED: BEC: 12ppt, LoD: 7ppt 75 As KED: BEC: 17ppt, LoD: 5ppt 2.5% HNO 3 / 1.5% HCl 21

22 QCell KED: Calibration Lines 100% Low Boiling Point Naphtha 22

23 QCell: Full Mass Range KED Analysis All single He KED mode 23

24 icap Qc ICP-MS for Clinical: Analysis of *20 Diluted Urine Accuracy (%) 200% 180% 160% 140% 120% 100% 80% 60% 40% 20% 0% Accuracy for UTAK Normal Urine control: Approximate adult normal range UTAK Urine normal Verified Value Expected Value 51 V Cr Mn Co Ni Cu Zn As Se Mo Pb All single He KED mode 24

25 Reactive Chemistry with the QCell Problem: Parent ions form oxide polyatomic interferences that interfere with target isotopes Solution: Introduce a reactive gas into the QC Mass Shift the interference away from the target isotope Example: Determination of Cd in the presence of Mo (e.g. in waste waters) is limited due to the formation of 95 MoO & 98 MoO at 111 Cd & 114 Cd Example: Add O 2 into the QCell, moving MoO to MoOx 25

26 icap Q ICP-MS: O 2 QCell 1ppm Mo 26

27 icap Q ICP-MS: O 2 QCell 1ppm Mo + 5ppb Cd 27

28 icap Q ICP-MS: O 2 QCell 1ppm Mo 1ppm Mo + 5ppb Cd 28

29 Measurement of Iodine 129 Radioactive nuclides of Iodine need to be monitored 129 I, t ½ 15.7 million years, β-decay 131 I, t ½ 8d, γ-decay Ar gas used for plasma generation may contain Xe impurities 129 Xe, 131 Xe create background signal Isobaric interference Not removeable with KED Use of 100% O 2 to generate XeO! 29

30 Effect of QCell Conditions 10ppb 127I (cps) 129I Background (cps) 129I BEC (ppt) Signal Intensity I BEC (ppt) Oxygen CCT Gas Flow (ml/min) 0.0 Optimum O 2 CCT gas flow obtained using the default CCT Autotune! 30

31 Performance of the Different Measurement Modes 127 I 129 Xe 127 I 129 Xe 127 I 129 Xe 127 I (cps) 129 Xe (cps) Blank 1,017 2, ppb Iodine 528,810 2,473 LOD: 6.9 ng kg -1 BEC: 50.9 ng kg I (cps) 129 Xe (cps) Blank ppb Iodine 49, LOD: 49.3 ng kg -1 BEC: 46.7 ng kg I (cps) 129 Xe (cps) Blank ppb Iodine 493, LOD: 0.08 ng kg -1 BEC: 0.95 ng kg -1 STD mode: Isobaric Interference clearly visible KED mode: Iodine Sensitivity drops CCT mode: No background from Xe, sensitivity comparable to STD mode 31

32 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 Element Sensitivity [cps ppb -1 ] STD mode* Sensitivity [cps ppb -1 ] KED mode* Sensitivity [cps ppb -1 ] CCT mode* Effect is especially pronounced for ions with m/z 100! Gain in sensitivity of a factor 2-3! Factor CCT/STD mode 7 Li 93, , Co 118,329 41, , In 255,203 72, , Ce 258, , , U 392, ,379 1,277, * Performance of a typical icap Qc model 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 ) ( 32

33 QCell: Collisional Focusing Performance 33

34 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) 59 Co In U

35 QCell: Collisional Focusing Performance 35

36 QCell: Collisional Focusing Performance 36

37 icap Qc ICP-MS: Collisional Focusing Isotope Ratios icap Qs He CCT Mode Self-aspiration 1ppb NBS SRM U Mcps/ppb U 10 * 1 min analyses <0.1% RSD <1% accuracy 37

38 icap Qc ICP-MS: Collision Focusing Lowers Abundance Sensitivity 10ppm U Standard: He CCT Mode Optimized pole bias 237/238: 57/3,579,950, *10-8 / ppm *30 better than standard specification 239/238(UH+ formation, non desolvation): 29ppm 38

39 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 39

40 Thank you for your attention! 40