Thin Layer and Gas Chromatography Flashcards
What is the TLC stationary stage? Give an example and what quality they have.
Material solvent/substance pass over
SiO2 / Al2O3
polar
What is the TLC mobile stage? Give an example
solvent
ethyl ethanoate (solvent)
What is the TLC process of separation?
Separation by adsoption
What is the Retardation factor? Give equation and which chromatography it’s used in.
Retardation factor = distance spot moved from baseline / distance solvent moved from baseline
TLC
What is the binding order of TLC? start with the smallest Rf factor
1st (shortest) binds very strongly, very polar, carboxylic acid
2nd binds strongly. polar, ester, aldehyde, ketone
3rd (furthest) binds weakly, non-polar, alkene, benzene
What does adsorption mean?
stick to or bind to the surface
What are the limitation of TLC?
- if it’s not on the database, no Rf value reference
- isomers cause overlapping spots, similar Rf values
- lack of separation of component spots due to solubility in solvent
What is the GC stationary stage? Give an example and quality
liquid hydrocarbon wax
(non-polar)
What is the GC mobile phase? Give an example
inert gas
N2/He
What is the definition of retention time?
Time taken between injection and emergence from the column
What is the GC process of separation?
Absorption
What is the order of absorption for GC? start with longest retention time
1st (longest retention time) - most soluble, least polar, alkanes and hydrocarbons
2nd - soluble, polar, carbonyls and esters
3rd (shortest retention time) - least soluble, polar, compounds with OH/NH4
How do you calculate concentrations from GC?
- run a series of GC’s on samples of known concentration
- plot a calibration graph of peak area against concentration
Explain how GC-MS is used to identify a sample?
- Run a GC of the mixture
- GC will separate the mixture into components
- for each component run a mass spectrum
- compare the mass spectrum to database of mass spectra of known compounds
