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30 Cards in this Set
- Front
- Back
What is the most widely used analytical technique
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Chromatography
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Chromatography definition
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a physical method of separation in which components to be separated are distributed between two phases
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Solutes which interact ___________ ____________ with the stationary phase take longer to pass through the column
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more strongly
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Solutes which only ___________ interact with the stationary phase
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weakly
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Adsorption chromatography
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solute adsorbed on surface of stationary phase
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Ion-exchange chromatography
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- Mobile anions held near cations are covalently attached to stationary phase
- Small molecules penetrate pores of particles - anion-exchange resin; only anions can be attracted to it |
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molecular exclusion chromatography
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- large molecules are excluded
- small molecules penetrate pores of particles |
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Partition Chromatography
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- Cross section of open tubular column
- solute dissolved in liquid phase bonded to the surface of column |
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Affinity chromatography
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- One kind of molecule in complex mixture becomes attached to molecule that is covalently bound to stationary phase
- all other molecules simply wash through |
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Longitudinal diffusion
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band slowly broadens as molecules diffuse from high concentration in band to regions of lower concentration
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what are the 5 commonly used GC Carrier gases
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1. helium 2. hydrogen 3. nitrogen 4. argon 5. CO2
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What is the most common detector for GC
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Flame ionization detector
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HPLC Normal Phase
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- hihgly polar stationary phase
- nonpolar solvent (mobile phase) |
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HPLC reversed-pase
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- nonpolar stationary phase
- polar mobile phase |
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what is the advantage of EOF
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NO eddy diffusion and mass transfer term
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Gravimetric analysis
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the mass of a product is used to calculate the orginal quantity of the target analyte in the sample
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percipitant
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a chemical reagent that causes precipitation of an analyte from a solution
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In gravimetric analysis, the precipitate should me
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1. pure
2. insoluble 3. Easily filterable 4. of known composition |
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What are the two phases of crystallization
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Nucleation and particle growth
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Nucleation
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where molecules in solution randomly form small aggregates of molecules
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Particle growth
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the addition of more molecules to the aggregate to form a crystal
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if nucleation >> particle growth
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many small aggregates
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If nucleation << particle growth
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large crystals
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Why is bad for nucleation to be faster than particle growth
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you wind up with many small particles in solution and few large ones
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Ways to improve crystal growth
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- raise the temperature
- add precipitant slowly - keep volume of solution large - control solubility through chemical means |
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homogeneous precipitation
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the precipitant is generated slowly by a chemical reaction
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Digestion
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promotes slow crystallization,
increases particle size, expulsion of impurities from the crystal |
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Ignition
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used to drive off water or give an oxide form
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thermogravimetry
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is a form of gravimetric analysis where mass is measured as a function of temperature
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Combustion analysis
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- used to determine elemental content of organic compounds burned in excess O2
- mass of CO2 and H2O is weighed |