ICP-MS ICP – Inductively Coupled Plasma MS – Mass Spectrometry

ICP-MS ICP – Inductively Coupled Plasma MS – Mass Spectrometry
Perkin-Elmer Elan 6100 DRC Thermo-Finnegan Element 2 Quad Element 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

ICP-MS Training - Cees-Jan De Hoog
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 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Instrumentation Quad low vacuum ~3x10-3 bar intermediate vacuum ~1x10-7 bar high vacuum ~5x10-10 bar ion beam 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Element Sample introduction 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Sample introduction: solids
Alternative sample introduction: laser ablation resolution: 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’ 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Argon plasma generates ions

Ionization in plasma 5 10 15 20 25 40 60 80 100 atomic number (z) ionization potential (eV) Cl F Se Ar He Ne As Kr Xe Hg >90% ionization 70-90% ionization 30-70% ionization 15-30% ionization <15% ionization K Rb Cs Ba Sr first second 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Ion extraction interface

Mass separation and detection
Quadrupole works as a mass filter Separates ions based on mass/charge ratio Quad Typical measurement time per mass unit: ms Analyzes more than 40 elements in less than 1 second! 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Mass separation and detection
Magnetic sector Element Magnet works also as a mass filter Allows higher resolution 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Isotopes - Isobars What we want to know What we measure Mass Element 39 40 41 42 43 44 Ar 99.6 K 93.3 0.01 6.7 Ca 96.9 0.65 0.14 2.08 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

ICP-MS spectrum (low resolution)
55Mn 63Cu 79Br 66Zn 65Cu 66Zn 58Ni 68Zn 60Ni 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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) 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Low vs. higher mass resolution
Quad Element (MR setting) 56Fe + 40Ar16O+ 56Fe 40Ar16O+ 55 56 57 55.92 55.95 55.98 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Dry vs. wet plasma 16O40Ar 56Fe ‘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. 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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) 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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) 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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? 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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) 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

External Standardization
blank level We mostly use multi-element standards: nitric acid solutions that contain elements Typical precision: 5% 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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 1 2 2 1 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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., 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., cps/ppb X) L.O.D. is 450 / = ppb 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

ICP-MS detection limits
better on Element than Quad 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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) 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Analytical accuracy and precision
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%: (±0.003) rsd=10%: 0.30(±0.03) High accuracy Low precision Low accuracy High precision 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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 ( L/min) on Element: varies little ( L/min) Aridus gas flows (if used, Element only) Ar (2-2.5 L/min) +N2 (3-9 mL/min) Check intensities Quad: 115In > Element: 115In > (Aridus) or > (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) 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

Optimizing the nebulizer gas flow
Called ‘plasma gas’ on Element 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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! 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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! 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

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 19/11/2018 ICP-MS Training - Cees-Jan De Hoog

ICP-MS ICP – Inductively Coupled Plasma MS – Mass Spectrometry

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