CHM 238 - Ch 12 - McMurray

CHM 238 - Ch 12 - McMurray - Chapter 12 Mass Spectrometry...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 12 Mass Spectrometry and Infrared (IR) Spectroscopy.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Spectroscopic Methods: Mass Spectrometry (MS) : Molecular size, formula, presence of some elements, … Infrared Spectroscopy (IR) : Molecular motion, functional groups, … Nuclear Magnetic Resonance Spectroscopy (NMR) : Molecular framework, … Ultraviolet-Visible Spectroscopy (UV-vis) : Conjugation of π -electrons, …
Background image of page 2
MS Instrument-Process: Three steps: Ionization : converts molecule M to M .+ . Mass analyzer : separates ions by mass/charge ( m/z ) . Detector : observes and counts ions . Sample Display Ionization EI, CI ESI MALDI Mass analyzer Magnetic Sector Time of flight Quadrupole Detector Photomultiplier Electron multiplier Micro-channel plate M M m/z m/z
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Ionization: The molecules to be analyzed must be converted into gas phase ions in order to be “weighed”. Generally, they are converted to cations, anions have also been used. Hard ionization (EI) induces the loss of an electron (M M + ). Soft ionization (CI, ESI, MALDI) gives a protonated molecule (M MH + ).
Background image of page 4
Ionization: Electron Impact (EI) In the vapor phase, molecules of our analyte are hit with high energy electrons. The electrons go though the molecule sometimes knocking another electron out of the molecule. Molecule RH M Organic molecule e - 2e - Molecular ion RH + M + Radical cation Mass analyzer
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Magnetic Sector Mass Analyzer: In a magnetic field, traveling charges are force to turn. Heavier ions turn more slowly than lighter ions. B Magnetic Field heavier ions lighter ions Detector M +
Background image of page 6
Mass Spectrum: Important Terms m/z : mass of ion divided by its charge. Mass spectrum : bar graph of m/z on x-axis and the relative abundance on the y-axis. Base peak : the m/z bar with the greatest abundance, is assigned 100%. The other m/z peaks are given valued at their percentage of the base peak’s abundance. Parent peak : also called the molecular ion, is m/ z peak that corresponds to the radical-cation of the molecule.
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Example Mass Spectrum of Pentan-2-ol Base Peak Parent Peak
Background image of page 8
Example Mass Spectrum In examining the mass spectrum, you should have noticed that there are a lot of other peaks besides the parent peak. These other peaks, of smaller m/z , are referred to as fragments . The ionized molecule is often unstable and breaks into smaller fragments. As we will see later, fragmentation can be useful in determining the structure of a molecule.
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
From the parent peak, the molecular mass is obtained, so that only compounds with that molecular mass would potential choices if it were an unknown substance. High-resolution MS instruments can provide
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 49

CHM 238 - Ch 12 - McMurray - Chapter 12 Mass Spectrometry...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online