Mass spectrometry gas phase transfer and instrumentation

Transcription

1 Objectives of the Lecture spectrometry gas phase transfer and instrumentation Matt Renfrow January 15, Make ions 2. Separate/Analyze 3. Detect ions 4. What is mass resolution and mass accuracy? Stable isotopes of most abundant elements of peptides Element Abundance H % C N O Monoisotopic mass Monoisotopic mass corresponds to lowest mass peak When the isotopes are clearly resolved the monoisotopic mass is used as it is the most accurate measurement. 1

2 Average mass Average mass corresponds to the centroid of the unresolved peak cluster ISO:CH3 How is mass resolution calculated? M R = M/ M 100 nsity % Inten 50 FWHM = M When the isotopes are not resolved, the centroid of the envelope corresponds to the weighted average of all the the isotope peaks in the cluster, which is the same as the average or chemical mass (m/z) Intensity (%) Two peptides - same nominal mass - simulation Peptide mixture: [Val 5 ]-Angiotensin II Lys-des-Arg 9 -Bradykinin Sequence: DRVYVHPF KRPPGFSPF Formula: C 49 H 69 N 13 O 12 C 50 H 73 N 13 O 11 Exact mass: [M2H] 2 = [M2H] 2 = m (mmu): 18.2 mmu (correct) RP = 18, (observed) (correct) m/z Intensity (%) RP = 56, ppm (10) m/z Is Accuracy Important? Results for error limit up to 5 ppm 1 ppm (4) 5 ppm (23) Theoretical Delta Delta RDB Composition [ppm] [mmu] C 49 H 71 O 12 N C 49 H 79 O 11 N 9 S C 41 H 75 O 14 N 15 S C 43 H 77 O 15 N 12 S C 48 H 75 O 16 N C 51 H 73 O 13 N C 47 H 69 O 11 N C 47 H 77 O 10 N 12 S C 44 H 73 O 11 N 16 S C 45 H 79 O 16 N 9 S C 52 H 69 O 9 N C 46 H 73 O 15 N C 38 H 79 O 14 N 15 S C 46 H 81 O 14 N 8 S C 45 H 75 O 9 N 15 S C 46 H 75 O 12 N 13 S C 52 H 75 O 11 N 9 S C 54 H 71 O 10 N C 44 H 71 O 14 N C 40 H 81 O 15 N 12 S C 44 H 79 O 13 N 11 S C 40 H 73 O 16 N C 48 H 77 O 13 N 10 S 1 2

3 error = theoretical mass - observed mass theoretical mass x 1,000,000 How does a mass spectrometer work? m/z = [ M nh] n m/z = [ M - nh] n Sample source: makes ions analyzer: separates ions spectrum: presents information Spectrometer Block Diagram High Vacuum System Spectrometer Block Diagram High Vacuum System Turbo molecular pumps Data source Analyzer System Data source Analyzer System 3

4 Sample Introduction Source High Vacuum System High Vacuum System Data Source Analyzer System Data Source Analyzer System HPLC Flow injection Charged vapor stream Sample plate MALDI ESI FAB LSIMS EI CI DART Nobel Prize in Chemistry For getting proteins and peptides into the gas phase Sources make ions from sample molecules (s are easier to detect than neutral molecules.) Electrospray ionization: Pressure = 1 atm Inner tube diam. = 100 um Sample Nozzle (Lower Voltage) Partial vacuum N 2 MH John Fenn Koichi Tanaka "for the development of methods for identification and structure analyses of biological macromolecules" and "for their development of soft desorption ionisation methods for mass spectrometric analyses of biological macromolecules" Sample in solution N2 gas High voltage applied to metal sheath (~4 kv) Charged droplets MH 2 MH 3 4

5 Electrospray ization (ESI) nebulizing gas sample solution HV N 2 curtain gas Analyzer Electrospray ization (ESI) Atmospheric pressure Vacuum 1. Solvent evaporation 2. Coulombic repulsion [M nh] n 5 m s Needle 1-5 kv power supply Electrospray ization (ESI) Process (Positive Mode) Taylor cone Site of Spray oxidation current ( i) ESI droplets Solvent and neutralized ions spectrometer Site of reduction Adapted from Kebarle, P and Tang, L, Anal. Chem., 1993, 65(22), 972A MALDI: Matrix Assisted Laser Desorption ization Sample plate h MH Laser /- 20 kv Grid (0 V) 1. Sample is mixed with matrix (X) and dried on plate. 2. Laser flash ionizes matrix molecules. 3. Sample molecules (M) are ionized by proton transfer: XH M MH X. 5

6 MALDI generation of ions (Matrix-assisted laser desorption ionization) Matrices for MALDI analysis Laser pulse (337 nm) [MH] [M-H] - matrix ions Peptide/protein deposited on crystal surface Sample mixed with a UV-absorbing matrix and is allowed to co-crystallize on the metal target. Peptides/proteins - 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid) - -cyano-4-hydroxycinnamic acid (CHCA) - 2,5-dihydroxybenzoic acid (DHB) - 2-(4-hydroxyphenylazo)-benzoic acid (HABA) Oligonucleotides - 2-aminobenzoic acid - 3-hydroxypicolinic acid (3-HPA) - 2,4,6-trihydroxyacetophenone (THAP) The choice of matrix depends greatly on the solute to be analyzed. Analyzer analyzers separate ions based on their mass-to-charge ratio (m/z) High Vacuum System Data source Analyzer System Time of flight (TOF) Quadrupole Trap Magnetic Sector FT-ICR MS Orbitrap MS Operate under high vacuum (keeps ions from bumping into gas molecules) Actually measure mass-to-charge ratio of ions (m/z) The importance of the mass-to-charge ratio is that according to classical electrodynamics two particles with the same mass-to-charge ratio move in the same path in a vacuum when subjected to the same electric and magnetic fields. F=ma (Newton s second law of motion) F=q(E v B) (Lorentz force Law) (m/q)a = E v B Key specifications are resolution, mass measurement accuracy, and sensitivity. 6

7 Time-of-flight (Tof) analyzer MALDI Laser; High Energy Monochromatic Light Source Principals of the MALDI-Tof/Tof time-of-flight flight (Tof) tube detector Accelerating pulse QSTAR TM ESI QQ TOF or MALDI QQ TOF Sample Quadrupole Analyzer Uses a combination of RF and DC voltages to operate as a mass filter. Q0 Q1 Q2 Has four parallel metal rods. Lets one mass pass through at a time. Effective Flight Path = 2.5 m Can scan through all masses or sit at one fixed mass. Mirror (reflector) 7

8 Quadrupole mass filter / ion guide QTRAP: Linear Trap on a Triple Quadrupole Q0 Q1 Q2 Q3 Exit Octapole linear ion trap funnel and mobility technology 8

9 PLkiI 3D ion trap and 2D ion trap 2D ion trap detection Conversion dynodes High Vacuum System source Analyzer Data System 9

10 2D ion trap detection Conversion dynodes (electron multipliers) Qtof Penning Trap (ICR cell) Triple quad Triple trap (Qtrap) funnel technology mobility 10

11 Penning Trap (ICR cell) magnetic field Put the trap in a high magnetic field cyclotron resonance 7 Tesla magnet, or 9.4 T or 12 T or 14.5 T 3D ion trap and 2D ion trap High Vacuum System Data source Analyzer System Microchannel Plate Electron Multiplier analyzer/ion trap AC image 11

12 2D ion trap detection Conversion dynodes Detecting in the ion trap cyclotron resonance (ICR) 7 Tesla magnet, or 9.4 T or 12 T or 14.5 T Fourier transform- cyclotron resonance FT-ICR MS ThermoFinnigan LTQ-FT m/z = k * B / f Frequencies are converted to masses. 12

13 LTQ Orbitrap Hybrid Spectrometer Finnigan LTQ Linear Trap API source Linear Trap C-Trap Orbitrap Analyzer k m / z Differential pumping Orbitrap Differential pumping Inventor: Dr. Alexander Makarov, Thermo Electron (Bremen) Data System The mass spectrum shows the results MALDI TOF spectrum of IgG High Vacuum System Data source Analyzer System Relative e Abundance MH (M2H) 2 PC (M3H) (m/z) 13

14 ESI Spectrum of Trypsinogen (MW 23983) M 16 H M 15 H M 14 H M13H m/z -to-charge ratio How do mass spectrometers get their names? Types of ion sources: Electrospray (ESI) Matrix Assisted Laser Desorption ization (MALDI) Types of mass analyzers: Quadrupole (Quad, Q) Trap Time-of-Flight (TOF) -Either source type can work with either analyzer type: MALDI- TOF, ESI-Quad. -Analyzers can be combined to create hybrid instruments. ESI-QQQ, MALDI QQ TOF, Q Trap Summary: acquiring a mass spectrum Objectives of the Lecture ization Source Form ions (charged molecules) Sorting (filtering) Analyzer Sort s by (m/z) 100 Detection Detect ions 1. Make ions ESI, MALDI 2. Separate/Analyze/Detect ions Tof, ion trap, quadrupole, FT-ICR, Orbitrap Electron multipliers Solid Liquid Vapor Spectrum 3. What is mass resolution and mass accuracy? 14

15 QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. 1/27/2014 Slide Acknowledgements Thermo Electron (Fisher) Bruker ABI Sandler Spectrometry Group David Agard group (Univ. of Calif. San Francisco) Put it in - We need s ( or - ) - In the gas phase Your machine - Tof, Tof / Tof - Quadrupole, trap - FT-ICR, Orbitrap (high resolution) -Hybrids Tell me the RIGHT answer - How right is it? mass resolution and accuracy MS of Proteins and Peptides 1D gel Put it in your machine and tell me the RIGHT answer 1D gel 2D gel 2D gel Protein mixture or Complex mixture Protein mixture or Complex mixture 15

16 Put it in - We need s ( or - ) - In the gas phase Your machine - Tof, Tof Tof - Quadrupole, trap - FT-ICR, Orbitrap (high resolution) -Hybrids Tell me the RIGHT answer - How right is it? mass resolution and accuracy Source Accelerating pulse Time-of-flight (Tof) analyzer Tof tube ( m) Effective flight tube (3.0 m) Reflector Resolution 2 x 10 4 No upper limit of mass Scan times ~ 1 sec, good for LC-MSMS s are accelerated so that they have equal kinetic energy. The ions drift down a meter tube before striking a photomultiplier detector. time of flight (t) depends on the mass of the ion (m), where t = (m/2ev) 1/2 *D V is the applied potential and D is the flight tube distance. For a given instrument, the flight time varies as the square root of the mass of the ion. Traps Expanded view of 3D ion trap The ion trap is an energy well - ions with sufficient energy to enter the trap are retained by an energy barrier on the exit side of the trap. The advantage of the ion trap is that it accumulates selected ions prior to their analysis giving it high initial sensitivity (detection limit of approx. 20 fmol). s are fragmented by collision with helium gas and their daughter ions analyzed within the trap. Selected daughter ions can undergo further fragmentation, thus allowing MS n. The ion trap has a high efficiency of transfer of fragment ions to the next stage of fragmentation (unlike the triple quadrupole instrument). 16