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ICP-MS

ICP-MS. ICP – Inductively Coupled Plasma MS – Mass Spectrometry. Perkin-Elmer Elan 6100 DRC. Thermo-Finnegan Element 2. Quad. Element. ICP-MS outline. Introduction Instrumentation Sample introduction Ionization in plasma Mass separation and ion detection Analytical procedures

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ICP-MS

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  1. ICP-MS ICP – Inductively Coupled Plasma MS – Mass Spectrometry Perkin-Elmer Elan 6100 DRC Thermo-Finnegan Element 2 Quad Element ICP-MS Training - Cees-Jan De Hoog

  2. ICP-MS outline • Introduction • Instrumentation • Sample introduction • Ionization in plasma • Mass separation and ion detection • Analytical procedures • Calibration • Interference corrections • Detection limits • Tuning • Data reduction • Sample preparation • Lab safety and etiquette ICP-MS Training - Cees-Jan De Hoog

  3. ICP-MS Training - Cees-Jan De Hoog

  4. Instrumentation Quad low vacuum ~3x10-3 bar intermediate vacuum ~1x10-7 bar high vacuum ~5x10-10 bar ion beam ICP-MS Training - Cees-Jan De Hoog

  5. Element Sample introduction ICP-MS Training - Cees-Jan De Hoog

  6. Sample introduction: fluids Samples are introduced with nebulizer which aspirates sample with high velocity Ar forming a fine mist Peristaltic pump Sample solution Aerosol passes into spray chamber where large droplets are removed via a drain. Only 2% of original mist enters the spray chamber. Processes yield droplets small enough to be vaporized in the plasma torch ICP-MS Training - Cees-Jan De Hoog

  7. Sample introduction: solids • Alternative sample introduction: laser ablation resolution: 25-300 µm depth profiling: ~1 µm/s d.l.s: 1ppm-1ppb • Some applications: • Trace elements in minerals • Growth zones in shells • Forensic and archeologic • ‘fingerprinting’ ICP-MS Training - Cees-Jan De Hoog

  8. Argon plasma generates ions ICP-MS Training - Cees-Jan De Hoog

  9. Ionization in plasma <15% ionization 15-30% ionization 30-70% ionization 25 He 70-90% ionization >90% ionization Ne 20 Ar F 15 Kr Cl Xe Hg ionization potential (eV) Sr As Ba 10 Se 5 K Rb Cs 0 0 20 40 60 80 100 atomic number (z) first second ICP-MS Training - Cees-Jan De Hoog

  10. Ion extraction interface ICP-MS Training - Cees-Jan De Hoog

  11. Mass separation and detection Quadrupole works as a mass filter Separates ions based on mass/charge ratio Quad Typical measurement time per mass unit: 10-20 ms Analyzes more than 40 elements in less than 1 second! ICP-MS Training - Cees-Jan De Hoog

  12. Mass separation and detection Magnetic sector • Magnet works also as a mass filter • Allows higher resolution Element ICP-MS Training - Cees-Jan De Hoog

  13. Isotopes - Isobars What we want to know What we measure ICP-MS Training - Cees-Jan De Hoog

  14. ICP-MS spectrum (low resolution) 55Mn 63Cu 79Br 66Zn 65Cu 66Zn 58Ni 68Zn 60Ni ICP-MS Training - Cees-Jan De Hoog

  15. Isobaric interferences • Isobaric interferences 40Ar+ on 40Ca+ (measure 44Ca+, only 2.1% abundance) 204Hg+ and 204Pb+ • Polyatomic interferences (oxides and archides) 40Ar16O+ on 56Fe+ (measure 57Fe+, only 2.2% abundance) 40Ar35Cl+ on 75As+ (monoisotopic) 40Ar23Na+ on 63Cu+ (measure 65Cu+,but watch 49Ti16O) 137Ba16O+ on 153Eu+ and 135Ba16O+ on 151Eu+ • Double-charged ions 90Zr++ on 45Sc+, 14N2+ on 7Li+ • Matrix dependent • Most elements have relatively interference-free isotopes (but they might be low in abundance) ICP-MS Training - Cees-Jan De Hoog

  16. Low vs. higher mass resolution Quad Element (MR setting) 56Fe + 40Ar16O+ 56Fe 40Ar16O+ 55.92 55.98 55 56 57 55.95 ICP-MS Training - Cees-Jan De Hoog

  17. Dry vs. wet plasma 56Fe 16O40Ar ‘Wet’ ‘Dry’ 16O40Ar 56Fe The Element has the option of a desolvator (called the Aridus). It is a spray chamber at high T (110°C) and has a membrane to separate water molecules from the sample. Reduces oxides more than 10x, increases sensitivity 5-10x. Drawbacks: increased memory effects, more difficult to tune, unreliable for volatile elements and As, Si. ICP-MS Training - Cees-Jan De Hoog

  18. Blank substraction • Even pure water gives a signal, so we need to correct raw data • Most significant for elements z<82 • Mostly results from molecular species from Ar gas and sample solution, e.g., ArO+, ArH+, ArOH+, ArC, CO+, CO2+ etc. • Match blank with sample matrix (‘sample without sample’) • Samples dissolved in 2% HNO3, then we use 2% HNO3 • Seawater: distilled water with 3.5% NaCl (and then dilute!) • Sequential extractions: the various extraction agents (e.g., HAc, NaAc, MgCl2, etc.) • Also corrects from small contributions from material deposited in sample introduction system (tubing, spray chamber, torch, cones) ICP-MS Training - Cees-Jan De Hoog

  19. Quantification • Correction for signal drift and signal suppression because of sample matrix: Internal Standardization • Blank correction • Calculation of element concentrations (external standardization) • Isobaric interference (overlap) correction • Data quality check (reference standards, duplicates) ICP-MS Training - Cees-Jan De Hoog

  20. Signal Drift One solution is to run standards often. But this is time-consuming, and what if you have many standards for many different elements? ICP-MS Training - Cees-Jan De Hoog

  21. Internal Standardization The assumption is that all elements behave similarly to In (1+2 from previous slide) • Also corrects for signal suppression due to matrix effects • Common internal standards: 115In, 185Re (45Sc, 6Li, 209Bi) ICP-MS Training - Cees-Jan De Hoog

  22. External Standardization blank level We mostly use multi-element standards: nitric acid solutions that contain 10-20 elements Typical precision: 5% ICP-MS Training - Cees-Jan De Hoog

  23. Other method 1: Standard Addition • Useful from samples with strong or unknown matrix • A spike with known concentration is added to sample • Precision similar to ES, but more accurate • Drawbacks • approximate concentration needs to be known • Labour intensive ICP-MS Training - Cees-Jan De Hoog

  24. Other method 2: Isotope Dilution • Addition of enriched isotope spike to sample • For ultimate precision and accuracy (better than 1%) • No internal standard necessary • Drawbacks • Approximate concentration needs to be known • Does not work for mono-isotopic elements • Labour-intensive and spikes often expensive natural ratio 2 1 2 1 ICP-MS Training - Cees-Jan De Hoog

  25. Elemental or isotope ratios • When you want to know the ratio of elements relative to one other element • Mg/Ca, Sr/Ca or other elements/Ca in forams, speleothems • When you want to do isotope ratios • Pb isotopes 207Pb/206Pb and 208Pb/206Pb • High precision needed • Sample bracketing (standard – sample – standard) • Preferably with standard composition close to samples • Standard and samples with similar concentrations • The ratio element or isotope serves as internal standard, does not need to be added ICP-MS Training - Cees-Jan De Hoog

  26. Detection limits • L.O.D. limit of detection (3x s.d. of the blank) • Measure a blank sample 6-10 times during run (e.g., 10000 cps for isotope X) • Calculate standard deviation (e.g., 150) • L.O.D. is 3x150 = 450 cps • Calculate cps/conc factor from standard for X (e.g., 10000 cps/ppb X) • L.O.D. is 450 / 10000 = 0.045 ppb ICP-MS Training - Cees-Jan De Hoog

  27. ICP-MS detection limits better on Element than Quad ICP-MS Training - Cees-Jan De Hoog

  28. Reference standards + blanks • Matrix often more complex than calibration standards • Unexpected interferences Measure something with known composition and similar matrix (Reference standards) • Sample digestion procedures involves many steps of adding acids, drying, etc., each will introduce some contamination Measure something without sample that has gone through whole dissolution procedure (digestion blanks) ICP-MS Training - Cees-Jan De Hoog

  29. Data processing • (SHOW EXCEL SHEET) • Normalize to internal standard (check for outliers which may indicate spiking errors • Calculate calibration line (Excel ‘slope’ function) from normalized intensities on standards and concentrations • Calculate concentrations of calibration blank + standards and check if ok • Calculate concentrations of samples incl. digestion blanks (include dilution factors) • Substract digestion blanks from samples • Correct for isobaric overlap (interferences) if measured • Evaluate precision and accuracy with duplicates and reference standards ICP-MS Training - Cees-Jan De Hoog

  30. Internal precision Precision on sample during analysis External precision Precision on several digestions of sample Accuracy Result on reference standard RSD vs. RSE RSE (=RSD/√n) improves with number of repeats, RSD does not Significant digits Should reflect precision E.g., rsd=1%: 0.304 (±0.003) rsd=10%: 0.30(±0.03) Analytical accuracy and precision High accuracy Low precision Low accuracy High precision ICP-MS Training - Cees-Jan De Hoog

  31. Instrument tuning • Torch position (x-y) if cones have been cleaned • Nebulizer gas flow (most important variable in wet plasma) • on Quad: dependent on autosampler that is used (0.9-1.1 L/min) • on Element: varies little (1.05-1.15 L/min) • Aridus gas flows (if used, Element only) Ar (2-2.5 L/min) +N2 (3-9 mL/min) • Check intensities • Quad: 115In > 20 000 • Element: 115In > 3 000 000 (Aridus) or > 400 000 (wet plasma) • Check oxide interferences (CeO+/Ce+) • <3% in wet plasma, <0.5% on Aridus (Element only) • Check doubly-charged ions (Ba2+/Ba+) • <3% in wet plasma, <6% on Aridus (Element only) ICP-MS Training - Cees-Jan De Hoog

  32. Optimizing the nebulizer gas flow Called ‘plasma gas’ on Element ICP-MS Training - Cees-Jan De Hoog

  33. Methods and Sequence/Batch • Software on Quad and Element are different, but principles are the same • Make a method • Select isotopes you want from a periodic table • Decide how long you want to measure each isotope • Decide how many repeats or runs • Set up a sequence (Element) or batch (Quad) • Put all blanks, standards, samples in a list, and indicate their position in the autosampler • Define which method you want to use • Indicate uptake and rinse times • Start! ICP-MS Training - Cees-Jan De Hoog

  34. Lab work, cleanliness & safety • Keep a lab book! • A record of sample handling • If something goes wrong you can track back what you did • Work clean • Wear gloves when handling samples • Clean equipment, vials, pipette tips, etc. before use (acid leach) • Lab coat (full body) in clean labs, incl. hood • Keep open samples in fume hoods if possible • Work safe • Very careful with strong acids and especially HF • Wear gloves and protective clothing • Clean up after use! ICP-MS Training - Cees-Jan De Hoog

  35. Check list • SAMPLE PREPARATION • Decide how to dissolve your samples • Keep a lab book • Work clean & safe • include digestion blanks + (if possible) reference standards • SAMPLE ANALYSIS • Book time in advance (a week at least, check with me) • Prepare samples and standards for analysis • Are the samples properly diluted? Keep signals <100 ppm! • Set up sample run in ICP-MS software • Tune instrument, start run • Clean up after use • Data processing and evaluation ICP-MS Training - Cees-Jan De Hoog

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