Applications of mass spectrometry in drug discovery Flashcards
What are the three main features of mass spectrometry?
Ionization Source
Mass Analyzer
Detector
Why do molecules of interest need to be ionized during mass spectrometry?
The detector measures the mass to charge ratio of a molecule to determine its molecular weight
Why does a mass spectrum for a single molecule yield many different peaks?
Charge can vary during ionization and change m/z, leading to different peaks
How can one get the isotopomeric molecular weight from a mass spectrum? Why are these masses different from isotopomer to isotopomer?
Multiply the m/z by the intensity (not relative)
Difference is due to presence/absence of protons
Why does each isotopomer have many, fewer peaks around it?
Isotopic envelope: gaussian distribution of isotopes with eg. C13 instead of C12 (highest peak is most common isotope)
What is the monoisotopic mass?
The mass of a substance if all atoms were the same isotope (often unlikely)
Is the average mass of a molecule greater than, equal to, or less than its monoisotopic mass? Why?
Greater
If you have a molecule with 769 Carbons, even at 1.1% incidence of C13 there’s at least 8 Carbons in your molecule (not to mention other molecules)
How do you calculate resolution?
Take a peak, find its maximum amplitude, then calculate the width at half the maximum amplitude
Called Full-width at half max (FWHM)
What is the difference between accuracy and resolution?
Accuracy: How “right” you are
Resolution: Grouping
What are two methods of non-fragmenting ionization, and two methods of fragmenting ionization?
Non-fragmenting: MALDI and ESI
Fragmenting: EI and FAB
How does MALDI work?
Analyte suspended in matrix of small organic compounds
Lazer is shone on matrix and gaseous ions are fed into MS
How does Electrospray Ionization work?
(Usually in tandem with liquid chromatography)
Little droplets are created from an inlet, a sheath of heated gas is fixed around
The heat dries the droplets, causes an excess of charges leading to electrostatic repulsion
End result is ions in gaseous phase
How is TOF measured?
Ions are allowed to accelerate in a vacuum chamber, and their acceleration time is dependent on their weight (with a known voltage, can use acceleration to calculate mass)
How is a Quadrupole used to detect mass?
Four charged rods alternate their frequencies, some frequencies cause certain m/zs to just fly out of the tube (can use this to filter out ions)
How does the Orbitrap work?
Ions get trapped in an ovoid shape and start spinning around, enough to drive a current (can use fourier transform to back calculate m/z)
