Instrumental Methods Exam 3 Flashcards
intersystem crossing
transition from a singlet to a triplet state
fluorescence
emission of a photon (after excitation with a photon) all states are singlet states
Phosphorescence
emission of a photon from a triplet state to a singlet state
internal conversion
moving between vibrational modes in one electronically excited state to a mode in another
external conversion
radiation-less decay, usually results from collisions
quantum efficiency of fluorescence
tells us the likelihood of observing fluorescence as a function of rates of decay pathway
combination modes
arise if a molecule has more than one mode
time domain spectroscopy
measures variations of electric field strength over time
Michelson interferometer
a device that slows down the signal
throughput or Jaquinot advantage
all light gets used, no loss in slits, minimal loss in optics
speed of acquisition “multiplex advantage”
easier to get more measurements quickly
raman spectroscopy
tells us about the vibrational modes of molecules but uses excitation source in VIS or near IR region, different vibrations are active
mass spectrometry
generates ions or ionic fragments of molecules and analyzes then as a function of mass to charge
electron impact ionization
electrons generate via thermoelectric effect from hot filament, accelerate across a moderate potential, and collides with and ionizes analyte
chemical ionization
ionizes some reagent ions which then react with and ionize analyte
common reagent ions
small molecules that do not tend to fragment
field desorption
electrode is dipped in sample held at high potential, mechanism is unknown but it has no fragmentation
MALDI
(matrix assisted laser desorption ionization) analyte embedded in sample matrix, laser shines on sample matrix, ionizes matrix which transfers charge to analyte, no fragmentation
electro spray ionization
liquid sample mixed with analyte, evaporation of solvent, coulomb explosion turns to charged analyte
quadrupole
selects m/z using 4 modes in pairs, each with an oscillating voltage so that only certain m/z have stable trajectories
magnetic sector analyzer
ions are accelerated across a potential and focused into a magnetic field, radius of curve shows m/z
double focusing
uses electric field to select particular KE - can improve resolution greatly
time of flight
detects m/z as a function of velocity (arrival time)
faraday cup
current flows through large resistor to neutralize accumulated positive charges - generated measurable voltage
electrochemical measurements
take advantage of reduction / oxidation reaction in which electrons are transferred between reactants
potentiometry
measures the strength of the driving force behind electrons
electrolytic cell
cells with current driven backwards
thermodynamics of cell potentials
measured voltage implies concentration are not at equilibrium
pH probe
glass membrane, constant H+ on the inside, variable H+ in analyte causes potential to develop across membrane
alkaline error
anytime the [H+] is similar to the positively charged alkali metals- probe will respond to those and report a lower pH than actual
acid error
at very low pH, you have populated all available sites, reports higher pH than actual
elution
the process by which compound become separated as they move through a column - driven by differential partitioning
chromatogram
plot of peak intensity vs time
band broadening
