Mass Spectrometry

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charged molecules (molecular fragments) generated in high vacuum move across spectrometer based on m/z

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Mass Spectrometry

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destroys sample into component functional groups

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Mass Spectrometry

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very good sensitivity, LOD & LOQ (better than UV/Vis)

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Mass Spectrometry

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Instrumentation of Mass Spec

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inlet -> ion source -> mass analysers -> detectors -> computer

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sample introduction

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1. direct insertion probe

2. online with chromatography system

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perpendicular movement of e- and sample

collision knocks off sample e- leads to charge

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ionization

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highly dependent on method of ionization

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appearance of mass spectra

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ionization sources

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1. gas phase sources

2. desorption sources

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sample is first vaporized then ionized

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gas phase sources

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sample directly converted to gaseous ions

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desorption sources

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ionizing agent for

1. electron impact

2. chemical ionization

3. field ionization

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1. energetic electrons

2. recent gaseous ions

3. high potential electrode

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ionizing agent for

1. field desorption

2. electrospray ionization

3. matrix-assisted desorption ionization

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1. high potential electrode

2. high electrical field

3. laser beam

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ionizing agent for

1. plasma desorption

2. fast atom bombardment

3. secondary ion mass spec

4. thermospray ionization

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1. fission fragments from 22Cf

2. energetic atomic beam

3. energetic beam of ions

4. high temperature

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GPS vs DPS

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GPS: thermally stable compounds, small molecules

DPS: nonvolatile & thermally unstable compounds, large moleculates

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causes lot of fragmentation

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hard sources

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impart sufficient energy on the analyte to leave the molecule in an excited state in w/c relaxation results in rupture of bonds

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hard sources

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hard sources

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pyrrolidine derivative

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causes little fragmentation w/ little peaks besides M peak

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soft sources

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electron impact

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hard sources

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chemical ionization

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partly hard sources

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field ionization

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soft sources

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bombardment w/ beam of energetic e-

e- produced accelerate towards positive target (anode)

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electron impact

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gaseous sample ionized by collision with ions produced by particle bombardment of an excess reagent gas

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chemical ionization

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types of chemical ionization

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1. positive ion CI

2. negative ion CI

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methane reacts with high energy e-

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PICI

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reagent gas collides with e- to reduce energy, then captured by EN groups

10x more efficient than EI, 40x more sensitive

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NICI

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heat first where sample is contained

little fragmentation occurs

ions formed under influence of large electric field

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field ionization

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separate ions based on m/z

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mass analyzers

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quadrupole mass analyzer

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time-of-flight mass analyzer

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ion capture/trap mass analyzer