4.1.5 - Analytical techniques Flashcards
what does desorption mean?
dissolving into the moving phase
what does adsorption mean?
attraction to the stationary phase
what is the mobile phase?
solvent - one that moves through the column
what is the solute (analyte)?
thing you are analysing
what does ‘like attracts like’ mean?
polar substances like polar solvents –> will be carried up together
how can you tell which substance has the highest affinity for the solvent (mobile phase)?
it is located at the top end of the chromatography sample
- little adsorption to stationary phase
how can you tell which substance has the highest affinity to the stationary phase?
located at the lower end of the chromatography sample
- little desorption into the mobile phase
what does Rf mean?
- retardation factor
- the distance that travelled over the solvent font.
- can depend on the polarity, ion charge or molecule size
how is the Rf calculated and how can the values be interpreted?
- for substances that are very soluble in the liquid, Rf will be close to 1 (high desorption)
- for substances that are rather insoluble in the liquid, Rf will be close to 0 (high adsorption)
what is column chromatography?
mixture moves down the column
- if like solvent = move quickly down
- doesn’t like solvent = move slowly/sticks to top
what is thin layer chromatography?
mixture moves up the plate
- if like solvent = moves up quickly
- if doesn’t like solvent = stay at bottom/ move up slowly
- retention factor used
what is the stationary phase/adsorbent?
- substance that stays fixed inside the column
what is the eluent?
fluid entering the column
what is the eluate?
fluid exiting the column (that is collected in flasks)
what is elution?
the process of washing out a compound through a column using a suitable solvent
what is the analyte?
mixture whose individual components have to be separated and analyzed
what is the Rt?
- retardation time
- the time to travel a distance
- can depend on the polarity, ion charge or molecule size
what is the protein analysis - chromatography size exclusion
- big molecules cannot penetrate the small pores in the stationary phase
- they are eluted by a volume between beads of the stationary phase
- small molecules penetrate the small pores.
- they are eluted by a volume of solvent equal to the total volume of mobile phase
- smaller get trapped in the pores and held by IMF. Larger ones will just pass over
what is mass spectrometry?
ionization of substances, separation and detection of the resulting ions generating a spectra
- atoms are ionized so the magnet will be able to deflect them
- the detector plate determines how many of each isotope is present
- the magnet is responsible for deflecting the ions
recall the process of obtaining a mass spectrum
- sample of a neutral molecule is vaporized
- blast with electron beam to ionize (formation of cations with no change in mass)
- loss of an electron results in a radical cation (no change in mass)
fragmentation occurs - mixture of charged and uncharged particles
- magnetic deflection separates charged particles by mass-to-change ratio, m/z (charge is usually +1)
- this results in a higher mass (highest molecular weight signifies the parent chain (molecular ion)
what are the components of a mass spectrum?
- detector records the frequency of each mass, the taller the peak, the more abundant the fragment
- the base peak: most abundant (rest are a comparison to this) which links to stability not amount in the structure
- parent peak/molecular ion: if unstable, highest is not the molecular ion (occurs when highly branched)
