Molecular Mass Molecular Mass SpectrometrySpectrometry

Mass Spectroscopy (MS)Mass Spectroscopy (MS)

The elemental composition of matter of samples

The structure of inorganic, organic and biological molecules

The quantitative and qualitative composition of complex mixture

Isotopic ratios of atoms in samples

MS - ComponentsMS - Components

Components of Mass Spectrometer

GC/MS System ComponentsGC/MS System Components

MS - IonizationMS - Ionization

Gas phase ionization (103 D):

Electron Impact (EI) – Energetic electron beam

Chemical Ionization (CI) – Reagent gaseous ions

Field Ionization (FI) – high potential electrode

MS - IonizationMS - Ionization Desorption Ionization (105 D):

Field Desorption (FD) – High-potential Electrode

Electrospray Ionization (ESI) – High Electric Field (20 kV)

Matrix – Assisted Desorption/Ionization (MALDI)

Plasma desorption (PD) – Fission fragments from 252Cf

Thermospray ionization (TS) – High temperature

MS - IonizationMS - Ionization

Hard source – enough energy to rupture bonds and producing fragments (EI)

Soft source – provides always molecular weight of the molecule (CI; ESI,

MALDI)

MS – Electron-Impact Ionization

MS – Ionization ChamberMS – Ionization Chamber

MS – Ring Component SpectrumMS – Ring Component Spectrum

MS - SpectraMS - Spectra

CH2Cl2

MW=84

1-PentanolMW=88

MS - ChromatogramMS - Chromatogram

MS – Isotopes AbundanceMS – Isotopes AbundanceMost Other Percentage (%)

H1 H2 0.015

C12 C13 1.08

N14 N15 0.37

S32 S33 0.8

S34 4.4

Cl35 Cl37 32.5

Br79 Br81 98.0

Si28 Si29 5.1

Si30 3.4

MS – Effect of Ionization Mode on SpectraMS – Effect of Ionization Mode on SpectraEI

Field Ionization

Field Desorption

Glutamic AcidHOOC-CHNH2 -CH2 – CH2 - COOH

MS – Ionization Mode and SpectraMS – Ionization Mode and Spectra

Electron- Impact

Chemical Ionization

1- DecanolMW = 158

MS – Chemical IonizationMS – Chemical Ionization

• Most often use reagent is CH4:

• Electrons will form several ions: CH4+; CH3

+; CH2

+

• Reactions (MH – sample molecule):

CH4+ + CH4 CH5

+ + CH3

CH5+ + MH MH2

+ + CH4 (M + 1)

CH3+ + CH4 C2H5

+ + H2

C2H5+ + MH M+ + C2H6 (M – 1)

(M + 29)

GC/MS – Jet SeparatorGC/MS – Jet Separator

GC/LC/MSGC/LC/MSSample Sample TransferTransfer

MS – Direct Sample IntroductionMS – Direct Sample Introduction

Direct Sample Probe

External Sample Introduction System

MS – Mass AnalyzerMS – Mass Analyzer• Resolution:

R = m/m

Where: m – mass of the first peak

m – difference between two adjacent peaks

Commercial MS have resolution 500 to 500,000

m = m/R

MS Analyzer – Magnetic Sector

MS – Electromagnetic AnalyzerMS – Electromagnetic Analyzer

Quadrupole MS Analyzer

MS – Quadrupole FilterMS – Quadrupole Filter

MS - Ion Trap Analyzer

MS – Time of Flight Analyser

MS – Reflectron Time of Flight Analyzer

MS – Fourier Transform AnalyzerMS – Fourier Transform Analyzer

Ion Cyclotron Resonance

Magnetic Field

GCMS - InstrumentationGCMS - Instrumentation

MS - InstrumentationMS - Instrumentation

LCMS – Electrospray Ionization (ESI)LCMS – Electrospray Ionization (ESI)

MS – Capillary ElectrophoresisMS – Capillary Electrophoresis

MS – Supercritical ChromatographyMS – Supercritical Chromatography

MS – Ion DetectorMS – Ion Detector

MS/MSMS/MS

MS/MS Instrumentation MS/MS Instrumentation

MS - CostMS - Cost

Mass SpectrumMass Spectrum

5-Ethyl-5n-hexyl barbituric acid

MW 240

MS - ChromatogramMS - Chromatogram

MS - QuantitativeMS - Quantitative

SIM – single ion monitoring

Spectra mode

Precision – 2% to 10%

MS – Spectra InterpretationMS – Spectra Interpretation

Base peaks and Relative Ion Intensities: Determine molecular ion mass. CI if needed.

Elemental composition from isotopic abundance: Look for A+2 pattern elements (Cl, Br, S, Si, O) Check A+1 ratios for absence/presence of S and Si Use the nitrogen rule to determine number of N’s (If

MW is even N=0 or even number. If MW is odd = odd number of nitrogen atoms

Estimate number of H, F, I, and P from isotopic ratios and MW balance (P is multivalent; F=19; I=127 mass units)

Check allowance for rings and double bonds. Number of double bonds or rings = x – 1/2y +1/2 z +1 (x=C, Si; y=H, F, Br, Cl; z=N, P, O, S)

MS – Spectra InterpretationMS – Spectra Interpretation

Use molecular ion fragmentation mechanism:Check fragment masses differences for expected

losses (Cl = 35; Br=79; Me=15; Et=29 etc…) Look for expected substructures Look for stable neutral loss (CH2 == CHR)

Look for products of known rearrangements

Postulate structures:Search library data base Run hit compound on the same instrument to

confirm

Use MS/MS if further confirmation is needed

MS - ApplicationsMS - Applications