Sep. & Spec.
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| Types of Chromatography | Adsorption (stick to surface), Partition (liquid phase bound to solid), Ion exchange, Molecular Exclusion, Affinity
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| Chromatogram | plot of detector signal vs. time
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| Retention time | How long a compound is retained in the solid/stat. phase. tr= tm + ts
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| Resolution | in chromatograph good resolution means good sep. of peaks (no overlap) and sharp
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| Dead Time | The time it takes for a non-retained analyte to move through
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| Avg. linear velocity | L/tm = u
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| Selectivity Factor | Way to measure peak sep. = Tra - Tm/Trb - Tm
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| Peak Broadening | Longitudinal Diffusion, mass transfer, diff. paths, fronting or tailing
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| Column Efficiency | Theoretical plates (N) = 16(tr/w)2
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| 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)
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| Increase efficiency | Change solvent system, faster push through, column length longer
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| Gas Chromatography | Injector, column, detector. GC separates based on 2 things - boiling point and polarity
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| Flame Ionization GC detector (FID) | read current flow as analyte hits flame burning gas and air, very sensitive, most organics
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| 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
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| Electron capture detector (ECD) | very sensitive, very specific for halogens, nitrates, nitirles, peroxides, some organometallic compounds. Creates ions and measures electricity flow
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| (PID) - Photoionization detector | Light causes electrons to be removed, creates ions; current flows between electrodes, good for volatile organic cmpds
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| GC/MS | Mass spectrometer can give definite identification of a molecule; lines correspond to mass
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| HPLC | High - Performance liquid chromatography - non - destructive and handles high boiling point analytes (large organics, peptides, etc)
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| HPLC system | pump, injector, precolumn, detector; thin tubing affects retention times and minimizes diffusion
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| Common HPLC Detectors | Uv-vis, diode array, fluorescence, mass spec, refractive index
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| Solvents for HPLC | Water, CH3OH, acetonitrile, 1%Ch3COOH or salts; separation is very sensitive to solvent polarity
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| Isocratic | solvent composition remains constant for entire separation
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| Gradient | solvent composition during the separation cahnges
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| 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
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| Spectroscopy | using light to study chemicals; light absorbance or emission
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| Light regions | 400-700 (visible), 50-400 (UV), 7000-50,000 (IR), microwaves - longer wavelengths, xray (<50)
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| 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
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| Limitations to UV-vis | Analyte must absorb in 190-800 nm range, can't be too concentrated, no structural info., slow if scanning samples
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| Speed up UV-Vis | Diode array detector - move the monochromater into the detector use photodiodes to detect all the wavelengths
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| 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
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| 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
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| 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
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| Fluorescence | photon emission in the singlet state
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| phosphorescence | relatively long life time, flips spin and then comes back down to ground state longer than fluorescence
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| vibrational relaxation | dropping down the vibrational states
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| advantages to fluor/phos | very sensitive, very selective (also a disadvantage since only some molecules do this)
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| 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
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| 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
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| NMR instrument | something emits rf and something detects it; plot intensity vs. ppm shift; res. increases as magnetic strength increases
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| Chemical shift NMR | a completely shielded nucleus, TMS used to 0 the instrument; shift depends on the electron environment around the proton
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| Beer's law | A=Ebc E= molar absortivity, b= path length, c = concentration
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| Relation between wavelength and frequency | frequency x wavelength = speed of light
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| Transmittance | A = -logT
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