Lecture_overheads_-_Ch21

Lecture_overheads_-_Ch21 - CHEM 321 Quantitative Analysis...

Info icon This 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
Image of page 1

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

View Full Document Right Arrow Icon
BOX DIAGRAM OF A MASS SPECTROMETER VACUUM SYSTEM
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
Image of page 3

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

View Full Document Right 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
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
Image of page 5

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

View Full Document Right 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
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) Disadvantages Limited dynamic range Requires high vacuum and fast detection circuits Long flight tube (up to 2 m in some cases) TOF – SUMMARY
Image of page 7

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

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

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern