1. Measurement of “Difficult” Elements and Isotopes Using a Hexapole ICPMS Zenon Palacz, Simon Meffan-Main. Micromass U.K. Ltd

2. “Difficult” Isotopes ! Argides (Ar, ArN, ArO, ArC) are Isobaric with transition metals and Calcium. ! 40 Ar- 40 Ca ! ArN- 54 Fe ! ArO- 56 Fe ! ArC- 52 Cr

3. Minimum Resolution Required to Remove Argides IsotopeInterferentRP 40 Ca 40 Ar192,500 80 Se 40 Ar 2 9,692 75 As 40 Ar 35 Cl7,771 56 Fe 40 Ar 16 O2,501 54 Fe 40 Ar 14 N2,087 52 Cr 40 Ar 12 C2,211

4. High Resolution Instruments.  Maximum resolution 10-15,000.  Increased resolution reduces transmission. (<5% at maximum resolution).  High resolution produces peak shapes without flat tops. Compromises precision of isotope ratios when peak jumping.  Single collector systems, so peak jumping necessary.

5. ICP Multicollectors  Low resolution (400).  Large peak flat and multicollection produce <10ppm precisions.  Cannot resolve argides to do multicollection at high resolution.  Can have one collector (axial) with adjustable slits to go up to 3000 resolution.

6. HEXAPOLE ICPMS  Hexapole collision cell removes argides, by colliding the argide molecules from the plasma, with an inert gas in the cell at room temperature.  Charge transfer with H in the hexapole can also neutralise Ar+.  Collisions in the cell reduces ion energy spread from plasma <1 volt, to allow single focusing magnetic sector.

7. Micromass IsoProbe

8. Sensitivity 10 8 9 11 250 150100500 Li Mg Fe Co Sr Rh Cs Nd Tb Pb Os Hf Th U In cps/ppm 3-4 eV 5-6 eV 6-7 eV 7-8 eV 8-9 eV 200 Ionization Potential Mass

9. Measurement of Pb Isotope Ratios

11. ArN from N 2 Sweep Gas in MCN 6000. No H in Collision Cell.

12. Mass Scan Across Cr and Fe in Water. Ar + H in Cell.

13. Mass Bias  ICP-MS has little or no time dependent mass fractionation, unlike TIMS.  ICP-MS has a mass dependent mass bias which increases with decreasing mass.  Elements of similar mass have similar mass bias.  Fractionation correction with a different element is possible.

14. IsoProbe Mass Bias Response Without B y = 8.5478 x -1.2874 R 2 = 0.9739 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 050100150200 Mass Mass Bias/amu Ca Sr, Zr & Mo Ag NdHf, W, Re & Os Pb & TlU B With B y = 7.1389x -1.2497 R2R2 = 0.9812 Cr & Fe Cu & Zn

15. IsoProbe Mass Bias Response  All elements fall on the same mass response curve.  If Argon or Argides were present this relationship would not occur.  The mass bias response is not effected by the type of gas in the collision cell. It must be created by fractionation across sample/skimmer cones

16. Cu and Fe Isotope Data 56Fe ion beam 8e-11A Baselines were measured at +/-0.5amu wrt to Fe. Block54Fe/56Fe%1se57Fe/56Fe%1se63Cu/65Cu%1se 10.0566490.00140.0258590.0052.06132230.0008 20.0566610.00160.0258850.00842.0615170.0014 30.0566630.0030.0258990.01712.06173560.0016 40.0566720.00160.0259350.0072.06204060.0009 50.0566740.00240.0259510.0132.06204130.0011 60.0566750.00150.0259740.00742.06205780.0013 70.056670.00250.0259950.0152.06204530.0014 80.0566670.00190.025930.0172.06183160.0011 mean0.0566660.0259292.0618239 1SD8.67E-064.58E-050.0002807 %1SD0.0152930.1764920.0136147

17. Mass Bias Correction  It is possible to correct for mass bias of one element with a different element. Pb-Tl U-Tl Fe-Cu  Accuracy requires precise understanding of the isotope ratio of the normalising element, and no isobaric interferences.

18. Mass Bias Correction for Fe  Exponential correction  54 Fe/ 56 Fen = 54 Fe/ 56 Fe m * beta  beta=(54/56)^(ln(( 63 Cu/ 65 Cu)ref/( 63 Cu/ 65 Cu) mes)*(ln(63/65)))  63 Cu/ 65 Cu ref = 2.2795

19. Cu Normalised Fe Ratios 54 Fe/ 56 Fe 57 Fe/ 56 Fe 10.06368490.024427 20.06369120.0244525 30.06368590.0244675 40.06368540.0245038 50.06368720.0245187 60.06368780.0245406 70.06368210.0245602 80.06368730.024497 mean0.06368650.0244959 1SD2.627E-064.497E-05 %1SD0.00412450.1835974

20. 54 Fe/ 56 Fe Ratio Measurements Using Different Techniques. 0.06355 0.06365 0.06375 0.06385 012345 TIMS External normalization Taylor et.al 1992 NTIMS Walczyk (1997) TIMS DOUBLE SPIKE ISOPROBE HEX-MULTICOLLECTOR Cu NORMALIZED 63/65 2.2795

21. 52 Cr/ 53 Cr vs Spike/Std concentration ( Errors 2 sigma St. Dev.) R 2 = 0.998 8.29 8.3 8.31 8.32 8.33 8.34 8.35 8.36 8.37 8.38 8.39 0.0000000010.000000010.00000010.0000010.000010.00010.001 Log Spike/Std concentration ratio 52 Cr/ 53 Cr 5ppb Cr standard 5ppb Cr standard with increasing amounts of 0.63ppb 53 Cr spike. 80  l 155  l 235  l 786  l

22. Conclusions  Argides are removed by the hexapole.  Argon is removed to allow 40 Ca measurements.  High precision Fe isotope ratios can be obtained at low resolution by normalisation with Cu.