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Polaris Q GC/MS n Ion Trap Technology

Polaris Q GC/MS n Ion Trap Technology. Steven T. Fannin. GC & GC/MS. The Column: “heart” of the Instrument. Maintaining GC/MS Ruggedness. “Extra Column” Effects Syringes Septa Liners Ferrules Gas Filters. Chromatography: General Overview. Resolution Selectivity

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Polaris Q GC/MS n Ion Trap Technology

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  1. Polaris Q GC/MSn Ion Trap Technology Steven T. Fannin

  2. GC & GC/MS The Column: “heart” of the Instrument

  3. Maintaining GC/MS Ruggedness “Extra Column” Effects • Syringes • Septa • Liners • Ferrules • Gas Filters

  4. Chromatography: General Overview • Resolution • Selectivity • Spacing between two peaks • Important role in GC confirmation analyses • Capacity Factor (Relative Retention) • Retention relative to an unretained compound • Column Efficiency: Why Capillary Columns? The Van Deemter equation: H = A + B/u + C u A: the multipath term (eddy diffusion)B: longitudinal diffusionC: resistance to mass transfer H = A + B/u + C u H = L/N N.B: Velocity: Pressure regulated vs Flow controlled H2 vs He vs N2

  5. Common Mass Analyzers for GC/MS • Time of Flight (TOF) - Ionized compounds/fragments from the source are directed into a flight tube. Ions are separated by virtue of their different flight times over a known distance. • Magnetic Sector - Uses a combination of magnetic and electrical fields to sort ions. The ions are focused and resolved by passing through an electric field then a magnetic field. • Quadrupole - consists of two sets on opposing rods. This mass analyzer uses a combination of RF and DC modulation to sort ions. • Ion Trap - operates on a principle as the quadrupole; however ions can be stored for subsequent analysis. The ions are sorted by changing the electric field inside of the trap by manipulating the RF field and sequentially ejecting the ions from low to high mass to charge.

  6. General Mass Spectrometry CharacteristicsWhat differentiates mass analyzers is how they perform mass analysis • Mass Analysis - Common to Mass Analyzers • All determine the m/z ratio • All measure gas-phase ions • All operate at low pressure (<10-4 Torr) to allow appropriate mean free path of gas phase ions • General Mass Spectrometry Instrument Characteristics • Sensitivity • Tandem Mass Spectrometry • Mass Range • Resolution • Mass Accuracy • Scan Speed

  7. GC/MS Ionization Methods

  8. Electron Ionization: EI (“Hard Ionization”) • Transfer of energy to a neutral molecule (in the gaseous state) to eject one of its own electrons and produce an ion (charged molecule), with a mass of m and a charge of z.

  9. Example of PFTBA EI+

  10. Chemical IonizationSoft Ionization Techniques Filament EI Ion Volume e- To Mass Analyzer CI Ion Volume CH4 Removable Ionization Volume Lenses

  11. Positive Ion Chemical Ionization • Reagent gas reactions (methane) m/z 16, 15, 14 m/z 17 m/z 29 m/z 28 m/z 27 m/z 41

  12. Positive Ion Chemical Ionization • Proton transfer • Hydride abstraction • Adduct formation [M+1]+ [M-1]+ [M+29]+ [M+41]+

  13. Common PICI Reagent Gases Proton Affinity* Hydride Ion Affinity* Reagent Gas • Methane [CH5+ & C2H5+] • Protonates most organic molecules • C2H5+ reacts with alkanes primarily by hydride abstraction • Isobutane [C4H9+] • Low purity (ion source gets dirty quickly) • Anhydrous ammonia [H+(NH3)n=1-3] • Very selective protonation (nitrogen compounds) • Forms [M+NH4]+ adduct with many compounds • Keeps ion source clean • Highly corrosive (short mech. pump lifetime) • 549 & 687 • 821 • 858 • 1126 & 1135 • 976 • 825 Less [M-H]+ with lower HIA Less fragmentation with higher PA reaction must be exothermic, i.e., PA (analyte) > PA (reagent gas) * kJ/mol

  14. EI vs.PICI for Pesticides PICI Spectrum of Heptachlor EI Spectrum of Heptachlor Intensity is concentrated in [M+H]+ ion. Spectrum is simpler. Intensity is low for any single m/z ion.

  15. Adduct Formation in PICI

  16. Negative Ion Chemical Ionization (EC-NICI) • Reagent gas reactions (methane) • Kinetic energy of electrons reduced by collisions with reagent gas • Resonance electron capture mechanism of ionization Thermal electron [M]- • Reagent gas reacts with electrons to form “plasma” of thermal electrons • Ionization is favored by molecules which have a high electron affinity – electron capture • Useful for selective analysis in heavy matrices, e.g., pesticides in food or waste matrix.

  17. Common NICI Reagent Gases e- Thermalization Rate* Reagent Gas • Methane • Isobutane • Low purity (ion source get dirty quickly) • Carbon dioxide • Can produce less fragmentation than methane or isobutane • Anhydrous ammonia • Keeps ions source clean • Highly corrosive (short mech. pump lifetime) • 8.6x10-10 • ~2.1x10-9 • 5.8x10-9 • 5.9x10-9 Better sensitivity with higher rate * cm3/s

  18. NICI of Carboxy THC - PFPA Negative Ion spectrum of the PFPA/PFPOH derivative of 11-nor-9-Carboxy-D9-THC

  19. Analysis of Catecholamines using NICI-MS 753 Pentafluoropropionyl (PFP) Derivatives of Norepinephrine, Epinephrine and Dopamine

  20. Ion Trap vs QuadrupoleBasic Principles

  21. +250 +1500 +V d c V R F 0 RF Potential DC Potential V R F +180° -V -1500 d c -250 Complete Mass Scan 77001-1380 970608 m/z Voltage Relationship During a Mass Scan (Quadrupole) • Ions scanned by varying the DC/Rf voltage across the quadrupoles +/-(U+Vocoswt) -/+(U+Vocoswt) Ion beam

  22. What is a Quadrupole Ion Trap? Ring Electrode Entrance Endcap Exit Endcap ro zo

  23. Potential Energy Surfaces (Ion Traps) V V V r z z z r r

  24. General Principles of Stability Diagrams Operating line for mass selective instability 0.4 z stability 1.0 0.2 0.8 b 0.1 0.7 Z 0.6 a 0.2 0.5 q ~.91 Z 0.4 0.3 c u t - o f f 0.3 0.2 0 0.4 qz 0.5 b X Y , -0.2 0.6 r stability 0.7 -0.4 0.8 Operating line for 0.9 Mass selective stability 1.0 8eV -0.6 qz = 2 2 2 m(r + 2 Z ) W O O 16eU az = 2 2 2 m(r + 2z ) W O O 0.5 1.0 1.5 q Z • Basic Ion Trap Principles • Mathieu stability diagram and stability/reduced parameters • Ion trap function : “Mass Selective Instability” • Quadrupole: Mass Selective Stability mode of scanning • The (a,q) coordinates are simply related to m/z and the operating voltage - whereas  values are related to ion motion ro zo

  25. Stability Line and Mass Selective Ejection Mass-selective Instability Scan with Resonant Ejection az 476 kHz 0.908 * 0.0 qz 1.0 Mass-selective Instability Scanning Ramp RF voltage (V) to sequentially eject ions from low m/z to high m/z.

  26. Trapping Injected Ions + + + + + + + ro zo • Correct RF voltage • Helium buffer gas

  27. Full Scan MS Scan Function Mass Analysis Mass Analysis Ion Injection Ion Injection V Gate Lens Eject (V’) Multiplier AGC Prescan* Mass Analysis Scan One complete scan constitutes a “microscan”

  28. Fixed Ion Injection Time Space Charge Effects 10 ms 0.1 ms DYNAMIC RANGE: ~103

  29. Ion Injection Time Optimized with AGC Space Charge Effects 5 µs** * User Selectable ** 5 µs PolarisQ, 10 µs LCQ, 30 µs GCQ Variable Time 250 ms* DYNAMIC RANGE: >106

  30. Polaris Q Tune Parameters (AGC and Injection RF)

  31. Quadrupole vs. Ion Trap Quadrupole quadrupoles use SIM to enhance sensitivity Transmits one m/z ion at a time Mass-Selective Stability scanning Ion Trap In full scan ion traps are more sensitive than quadrupoles. Trap all m/z ions simultaneously Mass-Selective Instability scanning

  32. Quadupoles and Sensitivity • Duty cycle is important for determining mass analyzer efficiency • Efficiency of the mass analyzer: • Ionization and mass analysis occur simultaneously: Mass resolution and scan range are important when determining duty cycle Quadrupole Transmits one m/z ion at a time Mass-Selective Stability scanning Duty Cycle for a Quadrupole Width of transmitted ion = Duty Cycle total width of m/z range

  33. Single Quadrupole Technology (single-stage MS techniques) SIM (Selected or Single Ion Monitoring) Set quadrupole to pass a single characteristic ion during a retention time window in the chromatogram Increases sensitivity 10-100X Lose spectral specificity MIM (Multiple Ion Monitoring) Monitor 2 to 5 characteristic ions in addition to SIM quanitiation ion Set acceptable qualifier ion “ratios” to confirm detection More qualifier ions boost confidence but reduce sensitivity gains Triple Quadrupole Technology (MS/MS Techniques) SRM (Single Reaction Monitoring) Single product ion monitored MRM (Multiple Reaction Monitoring) Multiple product ions monitored SIM, MIM and SRM,MRM (Target Compound Techniques)

  34. Ion Traps and Sensitivity • Efficiency of the mass analyzer: • Ionization and mass analysis occur consecutively: Scan time (or rate) relative to ion accumulation is important for determining duty cycle External Source Ion Trap Trap all m/z ions simultaneously Mass-Selective Instability scanning Duty Cycle for an Ion Trap Ion Accumulation Time (ion gate time) = Duty Cycle Total scan time

  35. Tandem MS Principles

  36. Tandem Mass SpectrometryWhy use MS/MS? • Enhanced Selectivity (Qualitative and Quantitative) • TRACE Analyses Criteria for Target Compounds • Sensitivity and Selectivity are important • MS/MS Improves Trace Level Analyses in complex matrices and enhances confirmatory analyses (Enhanced confirmation of identification) • Combined with Soft Ionization techniques • Most signal in [M+H]+ ions; Added selectivity and s/n • Confirmatory assays (MW ions plus 2-3 unique ions) • Qualitative and quantitative with digital reagent gasflow • Structural Characterization Applications • MS/MS provides unique evidence to an unknowns identity providing further information about fragments in the MS spectrum S/N TRACE DSQ uses SIM to increase S Polaris Q uses MS/MS to reduce N

  37. MS/MS “Tandem-In-Time”Ion Trap Technology MS/MS and MSn Capability MS/MS “Tandem-In-Space”Triple Stage Quadrupole Technology MS/MS “Tandem-In-Time”Ion Trap Technology

  38. MS/MS in an Ion Trap 3. Fragment 1. Inject 4. Detect 2. Isolate

  39. How Do We Isolate Ions for MS/MS? Mass-selective Instability Scan with Resonant Ejection az 476 kHz Ion we wish to isolate 0.908 * 0.0 qz 1.0 How MS/MS works qz Mp = VRF υ(ion) = (n + β) Ω/2

  40. Isolation Waveforms m/z 1000 Fast Fourier Transform m/z 300 m/z 100 Time Domain Frequency Domain

  41. CID using Resonant Excitation qz 0.0 0.908 How MS/MS works qz Mp = VRF υ(ion) = (n + β) Ω/2 t=15 ms Product ions qz 0.0 0.908

  42. Polaris Q Excitation Event Characteristics Excitation “q” 0.225 0.300 0.450 Stability Diagram: Where parent ions reside on the q axis during the excitation event qz P = precursor mass The choice of ‘q’ is also a function of the MS/MS lower limit of the product ion m/z range. A ‘q’ of 0.225 is 1/4Mp (where Mp is the m/z of the parent ion), and a ‘q’ of 0.3 is 1/3Mp, and a ‘q’ of 0.45 is 1/2Mp. For example, if a ‘q’ of 0.45 is used, and Mp is m/z 400, then the daughter ion lower limit that can be observed in the spectrum will be m/z 200. If the same ‘q’ is used for an Mp at m/z 800, then the daughter ion lower limit that can be observed will be m/z 400, and so on MS/MS qz Mp = VRF

  43. Higher qz Means Higher Energy Dz qz = 0.225 0.30 0.45

  44. Resonant Excitation qz Value Fragment ions not trapped Product Ion m/z Range Fragmentation Energy qz x 1/4 0.0 0.908 0.225 qz 2x 1/3 0.0 0.908 0.30 qz 4x 1/2 0.0 0.908 0.45

  45. Tandem MS: Polaris Q MS/MS Scan Function Mass Analysis Mass Analysis Ion Injection Ion Isolation Ion Isolation Resonant Excitation Ion Injection V Gate Lens Isolate Excite Eject (V’) How MS/MS works for all RF-Traps qz Mp = VRF υ(ion) = (n + β) Ω/2 Multiplier Mass Analysis Scan AGC Prescan

  46. MS/MS Example - Chlordane GC/MS Spectrum GC/MS/MS Product Ion Spectrum Fragment Precursor Ion Isolation of Precursor Ion

  47. Polaris Q MS/MS Parameters MS/MS Parameters Choice of Excitation q’s

  48. MS/MS: Optimizing Conditions ‘q’ is a function of the RF voltage applied to the ring electrode during excitation Excitation Event – higher excitation ‘q’s may provide improved conversion efficiencies (ECID =  Fi / P0)

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