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. |
