1	What is ICP-MS? Alan Koenig Research Geologist US Geological Survey Laser Ablation ICP-MS Facility Denver, CO
2	First a Few Questions Do we need ICP-MS or is ICP-OES o.k.? Just metals? Minor, trace or ultra-trace? Wide or narrow range of matrices? Just solids? Level of expertise/skills of operator? Research or routine?
3	Analytical Goals (Wishes?) Integrated system On-line quantification Fast and reliable Versatile with wide dynamic range ??
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5	Inductively Coupled Plasma Radio Frequency Ar plasma
6	ICP-MS Basics The ICP produces ions of the introduced material (liquid or solid aerosol) The MS extracts and detects those ions The interaction of ions in the plasma is matrix dependant (matrix and space charge effects) The ions are then brought to the detector through a variety of arrangements
7	Why ICP-MS? Improved sensitivity over OES, AA Higher throughput than GFAA Simpler interferences than OES (in some cases) Achieves required detection limits for alloys using Laser Ablation
8	Types of ICP-MS Instruments Quadrupole ICP-MS (most common) Scanning mass filter Scans 240 amu mass range 10 times/sec Very stable mass calibration ~ 1 amu mass resolution Sensitive for most elements down to ppt level Easy to operate and maintain
9	Types of ICP-MS Instruments Magnetic Sector or High Resolution ICP-MS Single collector and Multi collector Using a magnet and electrostatic analyzer arrangement capable of resolving very slight mass differences Operates at a range of mass resolution (usually low, medium and high) Very sensitive in low resolution mode (to ppq) Slower mass scanning (single collector) Expensive and more difficult to operate or maintain
10	Types of ICP-MS Instruments Multi-collector ICP-MS Similar arrangement to single collector but multiple detectors (up to 15) Very high precision (< 100 ppm) isotopic ratios Very sensitive ICP can ionize elements unable to be studied by TIMS- (Hf, Si, Cr, Hg, Cu, Fe, Zn + others…) Fast alternative to TIMS (200 Pb ratios in 2 days!) Still at methods development phase for many systems Expensive and more difficult to operate
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13	Matrix Decomposition
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19	The MS of ICP-MS Quadrupole
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21	“Chemical Resolution” Collision or reaction cell to combine with interfering species and be removed in the cell Reactions can be made to remove interferences or promote new ones… In some cases effective at removing interferences that cannot be resolved by other techniques
22	Collision or Reaction Cells Effective at removing the Ar₂⁺ interference on Se at mass 80 Reactions are often slow and complex Development still in progress for LA based methods Can be useful even without a gas in the cell
23	Other Types of Mass Analyzers
24	High Resolution or Magnetic Sector ICP-MS Alternative ion path design to quadrupole Ability to resolve isobaric interferences with higher resolution Uses a magnetic sector to separate ions by mass and an electrostatic analyzer to separate ions by energy Variable resolution (300, 4000 and 10,000) delivers flexibility in sensitivity versus resolution
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26	High Resolution ICP-MS Low resolution (R=300) Still better peak resolution than quad
27	HR-ICP-MS (cont.) Low resolution offers incredible sensitivity as compared to most quads Low resolution is most stable Medium resolution (R=3,000) offers intermediate resolution High resolution (R=8,000-10,000) offers the maximum resolution but suffers from reduced sensitivity and more mass drift Scanning may be slower than some quads
28	Dealing with Interferences Mathematical corrections High mass resolution Chemical resolution
29	Common Interferences
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31	Ni⁺⁺ Interference on P with a Quad
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33	Surface Contamination Same sample different days Surface moisture? Resolved at medium resolution
34	Multi-Collector ICP-MS
35	Detector Discrete dynode detector with 10⁸-10⁹ dynamic range Pulse counting (up to ~ 10⁶cps) and analog (10⁴ to 10⁸ counts) Detector lifetime is ion load dependant (1-3 years)
36	Overall Efficiency of a Quad ICP-MS
37	Sample Introduction Systems Standard liquid sample handling Nebulizers (low flow, high solids, etc.) Desolvators (Matrix removal) Flow Injection ETV (slurries) Laser and Spark ablation Other hyphenated systems GC, LC Others…
38	Pros Large dynamic range Ultra trace detection Resolution or correction of interferences are possible (and easier than OES) Liquids AND Solids Wide range of sample introduction systems (or schemes)
39	Cons Intolerant to high TDS or matrix levels (dilution is unfortunately often the solution) Vacuum system Interface contamination More expensive than OES Memory effects for some elements-especially with liquids
40	Random Comments Less matrix dependant than some others? Interferences can be complex, but not as bad as some others? Is it routine for your applications? How “automated” do you need it?
41	Key Points Robustness of the system Research or routine? Levels of detection Interferences
42	The US Geological Survey Research Chemistry Program The USGS has been a world leader in ICP-MS since 1985 The Research Chemistry Program is funded to develop new methods that help the greater geoanalytical community New development continues on instrumentation advances, sampling methods, speciation, isotopic analyses and many other While the primary focus of the USGS is geological, biological and environmental in scope, the USGS has partnered with numerous government and industry partners to help solve analytical problems
43	USGS Standards Program Since the development of the first interlaboratory rock standard in 1950, the USGS is recognized as a leader in the development of standard reference materials Today we continue to develop new and cutting edge SRMs for bulk and microanalytical analyses
44	Laser Ablation ICP-MS: Performance, Problems, Pitfalls and Potential Alan Koenig Research Geologist US Geological Survey Laser Ablation ICP-MS Facility Denver, CO
45	Introduction Laser Ablation ICP-MS can be considered the trace element microprobe The sensitivity of the ICP-MS for all trace elements is well known The use of a high energy laser as a sampling device provides direct in-situ measurements of trace elements in any solid (or gels, tar, goo, etc?) material Advances in laser technology, understanding the ablation process and new calibration standards are improving the accuracy, precision and spatial resolution of the technique
46	Laser Ablation (LA) LA-ICP-OES since 1984, LA-ICP-MS first in 1985 The interaction of a material and a high energy laser produces mechanical breaking of the material resulting in an aerosol of particles The exact mechanism of the ablation is complex (involves lots of physics) Advances in laser technology have improved results tremendously since late 80’s Shorter wavelength lasers are now used The ablated material is swept directly into the ICP from the LA system
47	LA Systems Today all systems are comprised of similar key components- The important differences are the laser wavelength Wavelengths Nd:YAG Solid State Lasers 266 nm, 213 nm (+/- 193 nm) Excited Dimer (Excimer) Lasers 193 nm (ArF gas) Significant research has shown shorter wavelength works best
48	LA Basics The spatial resolution (spot size) is from 2 mm to up to 1200 mm – LA system dependant Average spot analysis time is 2-3 minutes Entire 1 inch segment of sample can be scanned in ~ 20 minutes with 50 mm resolution
49	LA Basics (cont.) The material swept into the ICP from the laser should be small and not melted (IR lasers bad) The shorter wavelength lasers (< 200 nm) produce particles small enough to be properly ionized by the ICP For all wavelength lasers, matrix matched calibration standards are important! To account for variations in the transport and ablation of material and internal standard must be used for precise values
50	Benefits No sample preparation, digestion, contamination for prep Fast- up to 150 spot analyses day Spatial (temporal) information Trace element sensitivity Decreased matrix dependence as compared to SIMS or electron microprobe Flexible sample chamber for various sample geometries
51	Why Laser Ablation?
52	LA instead of Spark Small turnings Assessment of small inclusions Composition zoning Failure analyses of small zones or features
53	Limitations Sensitivity limited (sub ppm-ppb) at very small (< 25 mm) Still requires nearly matrix matched standard (not crystalline matched) For some applications there is still methods development evolution happening… Differences in reporting results Different lasers… Different standards…
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55	General Description Important to remember the LA system is not the detector, it is just a fancy way of getting your sample into the plasma We need to get these two systems to work together… LA optimization ICP-MS optimization Data handling
56	Ablation Mechanisms Thermal vaporization
57	Matrix Decomposition
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59	PFA-100 100 mL/min, 2000 ppm Y
60	Particles from Ablated Y₂O₃ Pellet
61	LA Crater in Glass