chem terms unit 2

Extraction

transfer of a solute from one phase to another

Adsorption

separation based on solute adsorption on surface of stationary phase

Partition

separation based on solute dissolving into stationary liquid

Ion-exchange

separation based on charge

Size exclusion or Gel Permeation

separation based on molecular size

Affinity

separation based on antibody-anitgen or enzyme-substrate interactions

Sensitivity

smallest concentration change that can result in a signal change

limit of detection

smallest amount of solute that generates a signal

Theoretical Plates

a number indicating how good a column is for a separation

Plate Height

Height Equivalent of a Theoretical Plate. Constant of proportionality between the bad variance and the distance it has traveled

Longitudinal Diffusion

Solute concentration is lower at the edges of a band; solute diffucses to the edges

Thickness of SP goes up, so does retention times. Why?

Solute spends more time interacting/dissolved in the SP b/c there is more of it. Partition coefficient favors SP (its greater)

Thicker SP does what to sample capacity

increases sample capacity

Thicker SP does what to early eluting peaks

improves resolution

Thicker SP does what to later eluting peaks

decreases resolution → broader peaks

Pros of OTC

higher resolution, shorter analysis time, greater sensitivity, no A term

Pros Packed column

better sample capacity

Thermal Conductivity → how it works

ability of a substance to transport heat away from hot region

Thermal Conductivity → features

GC, universal, not very sensitive, non destructive

Flame Ionization Detector → how it works

organic solutes burned in flame producing CH radicals 

Flame ionization detector → features

GC, organics, destructive, little better linear range

Electron Capture → features

halogens, nitriles, nitrates, conjugated double bonds, non destructive, most sensitive

Temperature programming cons

solubility variations, volatility changes, solute stability problems, flow rate changes, SP stability

Bulk Property

measures overall change in the mobile phase

Solute Property

measures a solute specific property

UV-VIS SPECTROSCOPY

solute property, universial <210

REFRACTIVE INDEX DETECTOR

bulk property, useless in gradient elution, universal

ELECTROCHEMICAL DETECTOR

bulk or solute property, very selective, no gradient

Common polar SP → NPLC

amino, cyano, diol

Common NP SP → RPLC

octadecyl, octyl, phenyl

Standard solutions

calibration curve to determine instrument or detector’s sensitivity

Standard addition

known quant of analyte added to unknown; from signal increase deduce how much analyte was in original unknown

Internal Standard

known amt of compound different from analyte added to unknown; compare signals to determine how much unknown is present

Capillary Electrophoresis

very fast, high efficiencies, especially useful for biopolymers

Electrophoresis

Separation is based on differences in migration of charged ions in an electric field in solution

Rate of Migration depends on

size of solute → larger size = more friction

charge of solute → greater charge, increased force

electroosmotic flow profile

hydrodynamic flow profile

Why is electroosmotic profile better

Surface charge “removes” friction between

solvent and walls of capillary

Pros of CE

no particles so no A term, no SP so no RMT (no C term)

Cons of CE

can increasing velocity by increasing voltage, but this generates heat which increases B