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Inductively Coupled Plasma Mass Spectrometry Dr. Lloyd Allen and Dr. Stuart Georgitis LECO Corporation 3000 Lakeview Avenue St. Joseph MI 49085.

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Presentation on theme: "Inductively Coupled Plasma Mass Spectrometry Dr. Lloyd Allen and Dr. Stuart Georgitis LECO Corporation 3000 Lakeview Avenue St. Joseph MI 49085."— Presentation transcript:

1 Inductively Coupled Plasma Mass Spectrometry Dr. Lloyd Allen and Dr. Stuart Georgitis LECO Corporation 3000 Lakeview Avenue St. Joseph MI 49085

2 Principles of Operation Spectrometer Componenets Sample Introduction System Sample Cell Optical Bench Detector Recorder or Computer

3 The ICP-MS Spectrometer ICP : Source of Ions –Atmospheric Argon based plasma –Operated from 2,500 to 8000 Kelvin to produce ions –Requires interface to vacuum bench Mass Spectrometer : Mass Filter or Mass Analyzer –Quadrupole –High Resolution Double Focusing –Ion Trap –Time-of-Flight

4 The ICP-MS Spectrometer (2) Sample Forms Possible –Solids : Conductive and Non-Conductive –Liquids : Aqueous and Organic –Gases Method Advantages –Very Low Noise = Very High Signal to Noise Ratio excellent detection limits (ppt) –Isotopic Analysis –Few interferences compare to other atomic techniques –Speed

5 The ICP-MS Spectrometer Qualitative Uses –Semi quantitation in the absence of standards, solids. –Concentration profiling –Isotopic Ratios = Dating, Finger Printing, Finger Pointing Method Disadvantages –TDS : typically < 0.2% –High Sensitivity = Contamination during sample prep. –Sequential systems have elevated RSD’s for Ratios –High resolution systems : Resolution > = < Sensitivity –Argide and Matrix Interferences

6 The Purpose of the Plasma Desolvation : Drying Droplets Vaporization : Particles to gas Excitation : Emission Atomization : Dissociation Ionization : Electron Loss e-e-

7 Radial Emission Med Energy Required (NAZ) Mn Compromise High Energy Required Short Wavelengths As, Se Low Energy Required Long Wavelengths K, Cs, La,Li, Na, Sr

8 The Plasma of ICP AES or MS –Frequency 27 Mhz 40 Mhz –Matching Network Crystal Controlled Free Running –Solid State –Mini-Torch or Standard ICP-MS Only –Secondary or Pinch Discharge Center Tapped Interlaced Coils Torch Shields –X, Y, Z Control

9 ICP-MS Components: Interface Ions must proceed from atmospheric pressure to an area of reduced pressure required for MS Plasma1st stage2nd stageAnalyzer stage Atmospheric Pressure ~ 1 torr10 -4 torr2 x torr Mechanical Pump (Interface) Turbo Pump Mechanical Pump (Backing)

10 The ICP-MS Interface Sampler Cone Skimmer Cone Barrel Shock Mach Disk Supersonic Jet Zone of Silence Torch & ICP Sample Ion lenses and Mass Analyzer

11 The ICP-MS Interface Torch & ICP Sample Sampler Cone Skimmer Cone Secondary Discharge Oxides, Polyatomics, secondary excitation

12 Velocity Consideration 4 eV, 100 amu ion 1964 m/s 14 eV, 100 amu ion 3674 m/s A factor of 2 reduction in ions in extraction volume

13 Ion Energies for Shielded Load Coil

14 Detection Limits (10s, 3 s) Shielded vs. Top-grounded

15 ICP Sample Introduction Systems Solution Nebulizers –Concentric –High Efficiency C. –V-groove –Modified Liechte –Cross Flow –Burgener Spray Chambers –Scott’s –Cyclonic’s –Inert or glass Ultrasonic Nebulizer –Membrane Desolvator Direct Injection Nebulizer Arc-Spark ETV Laser Direct Insertion Nebulizer Hydride Generator Discrete Sampling

16 ICP-AES and ICP-MS Inductively Coupled Plasma SimultaneousSequential PMT CID CCD PMT PMT’s Magnetic Sector Quadrupole ICP-AESICP-MSICP-AESICP-MS Magnetic Sector Time of Flight Ion Trap

17 The Two Major Approaches to ICP-MS Spectrometry Sequential : Mass Filters or Simultaneous : Mass Analyzer

18 Quadrupole ICP-MS A Sequential Mass Filter All m/z Values In One m/z Value Out Separation Based on Stability of the m/z Value in the RF and DC Fields on the Quadrupole Rods

19 Quadrupole ICP-MS RF 1, DC 1 RF 3, DC 3 Time 1 Time 2

20 Sequential Analysis Limitations: ICP-MS Sample throughput > = < a function of the number of m/z values measured –Transient Signals : very few isotopes analyzed ETV Chromatography Single spot laser ablation –Can not obtain high precision isotope ratios –Small volume samples: v. few isotopes analyzed –Susceptible to cones plugging (TDS) by prolonged sample contact

21 TOF ICP-MS Theory Simultaneous Mass Spectra KE = 1/2 mv 2 = zV m/z = 2V/v 2 m/z = (2Vt 2 )/(L 2 ) Velocity v = L / t Flight Tube Length (L) (+) Accelerating Voltage (V) Repeated up to 30,000 times per second

22 Requirements of TOF-ICP-MS Continuous ion beam requires modulation Detector must respond to fast ion events (ns) Data acquisition system must be able to handle TOF speeds Matrix ions must be removed to avoid detector saturation

23 Right-angle/Orthogonal Injection Repeller Acceleration Field Field-Free Flight Region Ion Lenses

24 Orthogonal TOF ICP-MS Disadvantages Transmission Efficiency at best 20% Sensitivity/Resolution Tradeoff Mass Dependent Optics in TOF due to mass dependent energies

25 Orthogonal Transmission  Detector Plane or Ion Mirror Original Ion Packet L= 0.5 to 0.75 m 23 mm dia. ion detector  v y / v x y x

26 Mass-Dependent Energies Repeller Acceleration Field Detector Ion Mirror Vsteer Green - Pb Red - Li Ion beam

27 Orthogonal Mass Bias M/Z CTS Low Mass Bias Mid Mass Bias High Mass Bias

28 Axial Mass Bias M/Z CTS

29 On-Axis Ion Injection Advantages Improved Ion Transmission Efficiency Reduced Mass Bias Reduced Optical Maintenance Reduced Instrument Footprint

30 Schematic Diagram of Axial TOF ICP-MS 123 Acceleration Extraction Skimmer Sampler Detector Ion Mirror ICP Torch Vacuum Stages Flight Tube

31 Simultaneous Mass Spectra Modulation (+) Repeated up to 30,000 times per second Accelerate to TOF RejectReject Rejec t 38 Micro S

32 Schematic Diagram of Axial TOF ICP-MS ICP Torch Ion Optic 1 Einzel 1

33 Ion Mirror Acceleration Field Detector

34 Simultaneous Advantages Transient Signals: complete multielement analysis High precision isotope ratios : Simultaneous Reads –no additive noise when employing corrections –no sample introduction or plasma noise Small volume samples: complete multielement analysis –minimum sample destruction –maximum spatial concentration profile capability Sample throughput =delivery and rinse time primarily Cone plugging via TDS exposure is minimized

35 Method Advantage : TOF Means Speed 30,000 Full Mass Spectra per Second U = Mach 115

36 Detection Limits Are They Signal To Background ? Or Signal to Noise? M/Z CTS

37 Detection Limits Are They Signal To Background ? Or Signal to Noise? M/Z CTS

38 TOF ICP-MS Detection Limits (3  ) ElementDL (ng/mL)ElementDL (ng/mL) Ba0.002Rb0.004 Co0.004Rh0.002 Cu0.004Sr0.002 Dy0.009Ta0.006 Er0.008Tb0.001 Eu0.003Th0.005 Gd0.005Tl0.008 Ho0.002Tm0.002 La0.003U0.004 Lu0.002W0.004 Nd0.009Y0.003 Pr0.002Yb0.005 Mn0.003V

39 Short Term Stability Internal Standard Results (20 min. 10 ppb)

40 Dual- Mode Detection 1 ng/mL100 ng/mL Analog Signal (mV) Ion Counting Signal (cps) Saturation

41 Dynamic Range

42 Dynamic Range (Counting and Analog)

43 LECO Patented Ion Counting/Analog Detection Scheme ETP AF831H 20 dB gain switching pre-amp 100 MHz Ion Counter 500 MHz flash A/D Windowed Buffer Dual Accumulator VME Bus

44 High Data Throughput Data throughput from ICP-MS up to 750 Mbytes/sec reduction is necessary for practical analysis Buffer retains 2000, 2 ns bins from each spectra Individual spectra are summed and the data transferred to the host computer Max bandpass 0.75 Mbytes/sec

45 Mass Mapping Mass Ar 14 N 2 68 Zn (impurity) 70 Ge 139 La (2+) 69 Ga 2 ppb Ga/Ge, 500 ppb La Time Bins

46 Bin Summation 255 Summed to 1

47 Figures of Merit and Applications Spectral resolution and matrix deflection Detection limits and speed of analysis Multielement transient signal analysis Isotope ratios and internal standards Solid sample analysis by LA

48 Quadrupole Resolution Low M/Z High M/Z 0.3 AMU 1.0 AMU

49 TOF Resolution Low M/Z High M/Z Unit Mass Baseline Resolved 1.0 AMU at Greatest Mass < 0.3 AMU at Least Mass with No Sacrifice in Sensitivity

50 TOF Resolution Low M/Z High M/Z

51 Lower Mass Resolving Power

52 Resolving Power at High Mass 50 ppt Pb, Bi

53 Resolution Selected Spectral Regions Expanded Cu + 64 Zn + 63 Cu + 62 Ni + 61 Ni + 60 Ni Co + 58 Ni Ba Ba Ba Ba Ba + m/z Pb Pb Pb Tl Pb Tl +

54 Quadrupole ICP-MS Matrix Filter RF 1, DC 1 RF 3, DC 3 Time 1 Time 2

55 TOF and High Matrix Low M/Z High M/Z

56 Coulombic Repulsion During Flight TIME

57 TOF and High Matrix Low M/Z High M/Z

58 Selectable Matrix Removal Flight Tube T.R.I.P. Transverse Rejected Ion Pulse Acceleration Repeller Modulation

59 Background Species Deflection (T.R.I.P.) NO + Ar + NO + O +, OH +

60 ICP-MS Speed Quadrupole vs TOF * Theoretical 0.3 sec. dwell time, 5 replicates, 60 sec. rinse time ** 3 points/peak, 10  s quadrupole settle time EPA (Analytes, Interference Corrections, Internal Standards)


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