Mass Spectrometry 1.pdf · 2008-02-05 · Mass Spectrometry. Only molecules of the correct m/z (mass/charge) will make it to the detector. Mass Spectromeric Isotope Indentification.

Analytical Chemistry

• Chromatography (Separations)

• Mass Spectrometry

• Infrared (IR) Spectroscopy

• Nuclear Magnetic Resonance (NMR) Spectroscopy

• X-ray Crystallography (visual solid state molecular structure)

What insights are we hoping to gain?

• Molecular Mass/Isotopic Distribution

• Molecular Formula

• Some Structural Characteristics – Fragmentation Pattern

Mass Spectrometry

Only molecules of the correct m/z (mass/charge) will make it to the detector.

Mass Spectromeric Isotope Indentification

EI-MS of 2,2-Dimethyl Pentane

Molecular ("parent") ion

Fragment ("daughter") ions

Base peak (largest signal)

Peaks with smaller m/z values __ called fragment ion peaks __

represent positively charged fragments of the parent molecule

EI-MS of 2,2-Dimethyl Pentane

Molecular iontert-butyl cation

(iso) propyl cation

Me Me

Me

methyl cation

ethyl cation

EI-MS of 2,2-Dimethyl Pentane

60

31

42

EI-MS of n-Propanol

EI-MS of 4-Heptanone

C3H7

OH

(iso) propyl cation

Molecular Ion

acylium ion

• +

EI-MS of 4-Heptanone

Molecular Ion

Why is there a signal higher than the Molecular ion?

EI-MS of 4-Heptanone

Isotopes

170 172

91

EI-MS of Benzyl Bromide

Isotopes

170 172

91

C7H779Br C7H7

81Br

Benzyl cation

EI-MS of Benzyl Bromide

EI-MS of 4-Chloroanisole

Isotopes

Isotopes