Lecture_overheads_-_Ch21

Lecture_overheads_-_Ch21 - CHEM 321 Quantitative Analysis...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
CHEM 321 – Quantitative Analysis Ch. 21 – Mass Spectrometry We’ll diverge from text and present MS topics in a more logical order 1. Instrumentation Overview Detector (electron multiplier) Mass Analyzers (TOF, quad, quad ion trap) Ionization Modes (EI, CI, ESI, MALDI) 1. Data Analysis Molecular weight (use to constrain molecular formula) Isotopic ratios (use to determine # Br, Cl, C) Library searching (use for compound identification via GC/EI/MS) Protein Sequencing (typically via LC/MS/MS) Quantitation
Background image of page 1

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

View Full DocumentRight Arrow Icon
BOX DIAGRAM OF A MASS SPECTROMETER VACUUM SYSTEM
Background image of page 2
MASS SPECTROMETRY INSTRUMENTATION Many different options for each component SAMPLE INTRO IONIZATION MASS SYSTEM SOURCE ANALYZER DETECTOR Solids probe Electron ionization Time-of-flight Faraday cup Gas chromatograph Chemical ionization (+, -, etc.) Magnetic sector Electron multiplier Liquid chromatograph Field desorption Dual sector Microchannel plate Ion chromatograph Field ionization Quadrupole Ion counting Capillary electrophoresis Plasma desorption Quadrupole ion trap Image current Continuous flow inlet Fast atom bombardment Linear ion trap Ion to photon Membrane inlet Electrospray Ion cyclotron resonance DART Laser desorption Fourier transform DESI Matrix assisted laser desorption ioniz’n Toroidal ion trap LDTD Secondary ion mass spectrometry Ion mobillity ASAP Spark source Orbitrap Glow discharge Inductively coupled plasma
Background image of page 3

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

View Full DocumentRight Arrow Icon
WHY IS A VACUUM NEEDED? An MS instrument requires a vacuum system such that, on average, a charged particle will undergo no more than a few low-energy collisions between the time of ionization and detection (unless you want it to – i.e., chemical ionization, fragmentation) Said another way – The mean-free path of an ion in a mass spectrometer should ideally be greater than the distance between where ionization and detection occur Typical pressures: ESI Source 1 atm CI Source 10 -4 Torr Quadrupole 10 -6 Torr TOF 10 -7 Torr FTICR 10 -10 Torr
Background image of page 4
ELECTRON MULTIPLIER D.W. Koppenaal et al, Anal. Chem, Nov 1, 2005, pp. 419A-427A Ion converted to electrons, current, then number Can use to detect positive or negative ions (requires conversion dynode) Can use discrete or continuous dynodes Most commonly used detector
Background image of page 5

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

View Full DocumentRight Arrow Icon
Source/extraction region Drift region Detector V E=V/d E=0 d L (KE = mv 2 /2) V = accelerating voltage E = electric field gradient d = distance of ion source region Operation • Ions formed as packet in source • Ions accelerated/extracted from source into drift region down a flight tube Ions arrive at detector in order of low to high m/z’s (different velocities/flight times) • Process repeats to acquire successive scans (mass spectra) TOF – BASICS
Background image of page 6
Advantages Medium to high resolution (R = 10,000 for some reflectrons) Virtually unlimited m/z range (simply wait long enough) Fastest scanning speeds (m/z 0-1000 @ 10,000 Hz!) Pulsed mode of operation makes this suitable for MALDI Simplicity (no slits or apertures, rods, or magnets)
Background image of page 7

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

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 48

Lecture_overheads_-_Ch21 - CHEM 321 Quantitative Analysis...

This preview shows document pages 1 - 8. Sign up to view the full document.

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