Instrumental Analysis

Calibration Sensitivity
m (slope of calibration curve)
Analytical Sensitivity
m/sigma (slope/standard deviation): depends on the error made when measuring at specific concentrations.
LOD
Limit of detection: 3sigma/m .
Photoelectric effect
Photoejection of an electron from the surface of a metal.
Ground State of a molecule
Lowest energy state
Electron excitation
Promotion of an electron from ground state to excited electron state
Blackbody Radation
Band of emission from a hot, glowing object
Fluorescence
Emission of light from excited state. Spin of electron does not change from original spin in ground state.
Light emission from singlet state
Phosphorescence
Emission of light from excited state. Spin HAS flipped from spin on ground state.
Light emission from triplet state
Snell’s Law
N(d)=sin(i)/sin(r) where i and r are degrees of incidence and refraction respectively
Dark current
Current out of a phototube or photodiode in absence of light
Transducer
sensor whose output is proportional to size of some physical stimuli
Scattered radiation
Stray light
Beam splitter
in reversed biased semiconductor zone where electrons and holes have left because they have migrated towards the electrodes.
Emission spectrum vs. excitation spectrum
Which resembles absorption spectrum?
Emission= excitation held constant, scans emission
Excitation-=emission held constant, scans excitation.
excitation like absorbance, excitation scanned
Resonance flourescence
wavelength of emission =wavelength of absorption
Singlet state
Spins same in excited and ground states
Triplet state
Spin flips in excited state
Vibrational relaxation
going from high to lower vibrational levels without emitting light
Internal conversion
Radiationless relaxation (mostly from vibrational levels with similar energies)
Intersystem crossing
switching between singlet and triplet states
Quantum yield
ratio of # of molecules in specific energy level to total number of excited molecules
Releasing agent
cation binds to interferant, releases analyte for analysis
Protecting agent
like EDTA,complexes out analyte but is volatile enough to be driven off in flame
Ionization suppressor
High concentrations of electrons to prevent ionization of analyte
atomization
vaporization and decomposition of sample into individual atoms
Pressure Broadening
High concentrations of atoms in flame cause broadening because of collisions
Hallow-cathode lamp
made of same material as analyte, sputters off electrons when the inert gas cations hits the glass tubing
Spectral interference
overlapping spectral lines
Chemical interference
releasing and protecting agents
Doppler broadening
atoms moving towards or away from detector are detected with different frequencies resulting in line width broadening
Virtual state
unquantized energy level that lies between quantized levels where scattering occurs
Magnetic anisotropy
Property of molecule that has magnetic properties that vary with orientation
screening constant
The measure of degree oto which circulation of electron around nucleus either reduce or increase the magnetic field felt by nucleus
sigma=(Bapplied-Bo)/Bo
Chemical shift parameter
measures shift in ppm of peak of given nucleus from that of a reference (usually TMS)
CW-NMR measurements
measuring amplitude of NMR signal as radio frequency is varied or field strength of magnet is scanned
Larmor frequency
frequency of precession of a nucleus in an external field
coupling constants
spacing in frequency units between peaks produced by spin-spin splitting
first-order NMR spectra
chemical shift between interacting groups is large with respect to their coupling constant
Elution
process in which species are washed through a chromatographic column
by the flow or addition of fresh solvent
e mobile phase
moves over or through an
immobilized phase that is fixed in place in a column or on the surface of a flat plate
stationary phase
solid or liquid that is fixed in
place.
distribution constant K
e ratio of the concentration
(strictly acitivity) of the analyte in the stationary phase to its concentration (activity) in
the mobile phase when equilibrium exists between the two phases.
retention time
time interval between its injection onto a
column and the appearance of its peak at the other end of the column
Longitudinal diffusion
source of band broadening in a column in which a solute
diffuses from the concentrated center of the band to the more dilute regions on either
side.
Eddy diffusion
molecules of an analyte reach the end of a
column at different times as a result of traveling through the column by pathways that
differ in length.
eluent
fresh mobile phase that carries the analyte
through the column.
zone broadening
(1) large particle diameters for
stationary phases;
(2) large column diamters;
(3) high temperatures (important only in GC)
(4) for liquid stationary phases, thick layers of the immobilized liquid;
(5) very
high or very low flow rates.
Gradient elution
method of performing liquid chromatography in which the
composition of the mobile phase is change continuously or in steps in order to optimize
separations.
isocratic elution
solvent composition is held constant throughout the
elution
gradient elution
two or more solvents are used and the composition of the
mobile phase is changed continuously or in steps as the separation proceeds.
reversed-phase packing
nonpolar packing that is used in partition
chromatography with a relatively polar mobile phase.
normal-phase packing
stationary phase is polar and the mobile phase is
relatively nonpolar.
Sparging
process for removing dissolved gases from a solution by sweeping the
liquid with a stream of fine bubbles of an inert gas of low solubility.
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