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mass spectrometry. FOS 6355 Summer 2005. Russell Rouseff. What is Mass Spectroscopy Analytical Chemistry Technique Used to identify and quantify unknown compounds Can also elucidate structure and chemical properties Sensitive technique As little as 10 -12 g can be analyzed

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russell rouseff

mass spectrometry

FOS 6355

Summer 2005

Russell Rouseff

slide2

What is Mass Spectroscopy

    • Analytical Chemistry Technique
    • Used to identify and quantify unknown compounds
    • Can also elucidate structure and chemical properties
    • Sensitive technique
      • As little as 10 -12 g can be analyzed
    • Identification based on molecular fragmentation patterns
      • fragments are separated by their m/z ratio
slide3

1899 - Early Mass Spectrometry

1943 - Double focusing analyzer

1946 - Time of Flight MS

1947 - Preparative Mass Spectrometry

1953 - Quadrupole MS

1956 - GC/MS

1956 - Identifying Organic Compounds

1966 - Chemical Ionization

1966 - Peptide Sequencing

1968 - Atmospheric Pressure Ionization

1978 - GC-C-IRMS

1980 - Inductively Coupled Argon Plasma

1990 - Protein Structure

1993 - Protein Mass Mapping/Fingerprinting

1996 - MS of a virus

1996 - First proton transfer MS

MS Time lines

1885

1905

1925

1945

1965

1985

2005

slide4

Mass Spectroscopy Applications

    • Detect and identify the use of steroids in athletes
    • Monitor the breath of patients by anesthesiologists during surgery
    • Determine the composition of molecular species found in space
    • Determine whether honey is adulterated with corn syrup
    • Monitor fermentation processes for the biotechnology industry
    • Detect dioxins in contaminated fish
    • Establish the elemental composition of semiconductor materials
    • Perform forensic analysis – arson identification
    • Determine exact atomic mass and isotope abundance
slide5

Objectives

    • How did mass spectrometry originate?
    • What is a mass spectrometer?
    • What are the characteristics of a mass spectrum?
    • How is the sample introduced into the mass spectrometer?
    • How are the molecules and fragment ions produced in the ion source?
    • How does the analyzer work?
    • How does the detector work?
    • What are the roles of computers in mass spectrometry?
slide6

Objectives

    • How can mass spectrometric data be used for structure analysis?
    • What other techniques are used to produce ions?
    • How large a molecule can be analyzed?
    • How is mass spectrometry used with GC,LC, and other separation techniques?
    • How is mass spectrometry used for quantitative analysis?
    • What is mass spectrometry/mass spectrometry (MS/MS)?
    • What is isotope ratio mass spectrometry?
slide7

Vacuum pumps

Ion Formation

Ion Sorting

Ion Detection

source

analyzer

ion

detection

data

system

Data Handling

Sample

Introduction

Data Output

Mass spectrum

slide8

Sample Introduction

    • Neutral molecules in gaseous state
    • Can be either liquid, solid or gas under STP
      • must volatilize under vacuum
    • must be pure
    • often coupled with GC, HPLC or CE
      • but can use solids probe if pure
slide9

Ionization Techniques

    • Electron Impact, EI
    • Chemical Ionization, CI
    • Fast Atom Bombardment, FAB
    • Atmospheric Pressure Chemical Ionization, APCI
    • Proton Transfer Reaction
slide11

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Ion Formation (EI)

Electron collector

Ion focusing lenses

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repeller

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Sample

entrance

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filament

slide12

CO2+

Molecular ion

Base ion

O+

CO+

C+

slide14

Sample Ionization

    • Electron Impact, EI, most common
    • 70 eV standard ionization energy
    • M + e- => M+ + 2e-
    • But sometime 70 eV too powerful
slide17

Chemical Ionization

    • A softer ionization technique
    • Use ionized molecules to transfer protons (+)
    • M + CH5+ => (M+H)+ + CH4
    • Chemical Ionization gases
      • methane
      • isobutane
slide19

Chemical Ionization

    • Produces spectra with little fragmentation
    • However, no standard spectral libraries
    • Spectra tends to be instrument specific
      • reagent gas pressures, ionization efficiencies
    • Must generate own standards
slide22

Large Molecule Ionization

Can routinely analyze molecules of 10,000 Da or more

Upper limit used to be 2,000 Da

slide23

APCI

  • A form of chemical ionization
  • Used for LC/MS interfaces
  • Allows for removal of solvent before vacuum
slide25

Proton Transfer Mass Spectrometery

glow

discharge

H30+ + M => (M + H) = H2O

M+

H30+

M+

M

H30+

Europhysics News (2004) Vol. 35 No. 6

slide26

Proton Transfer Mass Spectrometery

Produces spectra with little ionization, quantify using M+

Detects aroma compounds at ppb levels

Europhysics News (2004) Vol. 35 No. 6

slide28

Mass Analyzer Types

    • Magnetic Sector
    • Quadrupole mass analyzers
    • Ion trap
    • Time of flight
slide29

Magnetic Sector Mass Spectrometers

e-

Molecular

Source

Ionization

chamber

H0

Magnetic Field

Exit slit

detector

slide30

Magnetic Sector Disadvantages

    • Not well-suited for pulsed ionization methods
    • Very High cost
    • Large size
    • High maintence costs
slide31

quadrupole mass analyzer

detector

resonant ion

nonresonant ion

quadrupole rods

source

Mass filters

focusing lens

slide32

Quadrupole Advantages

    • Classical mass spectra
    • Good reproducibility
    • Relatively small/ compact
    • Relatively low-cost systems
    • Can improve sensitivity 100x with SIM
slide33

Quadrupole limitations

    • Limited resolution
    • Peak heights variable as a function of mass (mass discrimination).
      • Peak height vs. mass response must be 'tuned'.
    • Not well suited for pulsed ionization methods
slide35

Ion Trap Advantages

    • High sensitivity
    • Multi-stage mass spectrometry, MSn
    • Compact mass analyzer
slide36

Ion Trap Limitations

    • Requires careful quantitation
    • Limited dynamic range
    • Subject to space charge effects and ion molecule reactions
    • No sensitivity gain using SIM
slide39

General Mass Spectrometry Sites

  • ASMS- American Society for Mass Spectrometry
  • http://www.asms.org/whatisms/edu_resources.html
  • Excellent educational MS resource with many MS related links.
    • Cambridge University WWW Mass Spectrometry Serverhttp://www-methods.ch.cam.ac.uk/meth/ms/theory/index.html
    • Comprehensive site with information on ionization processes, mass analyzers, and other mass spectrometry techniques.
    • Organic Chemistry Online
    • http://chipo.chem.uic.edu/web1/ocol/spec/MS.htm
    • Introductory information about analysis of organic compounds by electron impact mass spectrometry, tables of common fragment losses.
    • University of Leeds:  Introduction to Mass Spectrometryhttp://www.astbury.leeds.ac.uk/Facil/MStut/mstutorial.htm
    • Introductory site focusing on the analysis of biochemical samples.
    • Information on Specific Techniques
slide40

Misc. Mass Spectrometry Sites

Sheffield ChemPuter: Isotope Patterns Calculator

http://www.shef.ac.uk/chemistry/chemputer/isotopes.html

Site predicts isotope pattern based on molecular formula.

UCSF Protein Prospector

http://prospector.ucsf.edu/

Site includes useful programs for analyzing the mass spectra of proteins and peptides.

Proteomics tools for mining sequence databases in conjunction with Mass Spectrometry experiments