Instrumental Analysis Answers – Flashcards

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