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Sep. & Spec.

QuestionAnswer
Types of Chromatography Adsorption (stick to surface), Partition (liquid phase bound to solid), Ion exchange, Molecular Exclusion, Affinity
Chromatogram plot of detector signal vs. time
Retention time How long a compound is retained in the solid/stat. phase. tr= tm + ts
Resolution in chromatograph good resolution means good sep. of peaks (no overlap) and sharp
Dead Time The time it takes for a non-retained analyte to move through
Avg. linear velocity L/tm = u
Selectivity Factor Way to measure peak sep. = Tra - Tm/Trb - Tm
Peak Broadening Longitudinal Diffusion, mass transfer, diff. paths, fronting or tailing
Column Efficiency Theoretical plates (N) = 16(tr/w)2
Factors affecting column efficiency Linear velocity of mobile phase, diffusion coeffiecient in mobile phase, diffusion coefficient in stat. phase, retention factor, diameter of solid particles, capillary columns (thinner is usually better)
Increase efficiency Change solvent system, faster push through, column length longer
Gas Chromatography Injector, column, detector. GC separates based on 2 things - boiling point and polarity
Flame Ionization GC detector (FID) read current flow as analyte hits flame burning gas and air, very sensitive, most organics
Thermal Conductivity Detector (TCD) universal and good for inert gases, wire is sensitive to temperature changes, measure current flow through the wire, resistance changes as temp changes
Electron capture detector (ECD) very sensitive, very specific for halogens, nitrates, nitirles, peroxides, some organometallic compounds. Creates ions and measures electricity flow
(PID) - Photoionization detector Light causes electrons to be removed, creates ions; current flows between electrodes, good for volatile organic cmpds
GC/MS Mass spectrometer can give definite identification of a molecule; lines correspond to mass
HPLC High - Performance liquid chromatography - non - destructive and handles high boiling point analytes (large organics, peptides, etc)
HPLC system pump, injector, precolumn, detector; thin tubing affects retention times and minimizes diffusion
Common HPLC Detectors Uv-vis, diode array, fluorescence, mass spec, refractive index
Solvents for HPLC Water, CH3OH, acetonitrile, 1%Ch3COOH or salts; separation is very sensitive to solvent polarity
Isocratic solvent composition remains constant for entire separation
Gradient solvent composition during the separation cahnges
Reverse Phase HPLC column is less polar C18; solvent = mobile phase is more polar; analyte movement is based on polarity, polar solvents tend to increase pressure
Spectroscopy using light to study chemicals; light absorbance or emission
Light regions 400-700 (visible), 50-400 (UV), 7000-50,000 (IR), microwaves - longer wavelengths, xray (<50)
UV-Vis instrument Lamp, monochromator, beam splitter sends light to sample and reference, chopper makes sure both don't hit the detector at once, PMT, amplifier, display
Limitations to UV-vis Analyte must absorb in 190-800 nm range, can't be too concentrated, no structural info., slow if scanning samples
Speed up UV-Vis Diode array detector - move the monochromater into the detector use photodiodes to detect all the wavelengths
Bandwidth wider slits give more light on the sample but allows a wider range of wavelengths to reach the detector (lose resolution); higher intensity = less resolving power; narrower slits give lower intensity and better resolution
PMTs photo multiplier tubes - light hits surface and wire is at +80 volts, when photons hit the electrons willb e ejected and this creates a current
Kinetics zero order - reactant conc. has no effect on the rxn rate; 1st order - 1 reactant conc. controls the rxn rate; 2nd order - 2nd order in 1 reactant, relies on conc. squared or 1st order with 2 reactants, hold one constant and change other
Fluorescence photon emission in the singlet state
phosphorescence relatively long life time, flips spin and then comes back down to ground state longer than fluorescence
vibrational relaxation dropping down the vibrational states
advantages to fluor/phos very sensitive, very selective (also a disadvantage since only some molecules do this)
Fluor/Phos instrument xeon arc lamp, excitation mono to ref. and sample, then a 90 degree turn in the sample to an emission mono, then to PMT
NMR a form of absorption spectrometry under certain conditions in a mag. field; a sample can absorb rf radiation which depends on the nuclei in the molecule
NMR instrument something emits rf and something detects it; plot intensity vs. ppm shift; res. increases as magnetic strength increases
Chemical shift NMR a completely shielded nucleus, TMS used to 0 the instrument; shift depends on the electron environment around the proton
Beer's law A=Ebc E= molar absortivity, b= path length, c = concentration
Relation between wavelength and frequency frequency x wavelength = speed of light
Transmittance A = -logT
Created by: eannl25