ANALYSIS OF ORGANIC COMPOUNDS
CHROMATOGRAPHY
High-performance liquid chromatography (HPLC)
solids in HPLC columns = e.g. alumina (Al2O3) , silica (SiO2)
stationary phase = e.g. paper
mobile phase (moving) = e.g. water
adsorption onto s.p = adhesion of molecules to surface
desorption/ dissolving onto m.p
polar m.p = more polar components tend to move quickly than less polar components = soluble components move further up stationary phase in time interval
Thin-layer chromatography (TLC)
thin layer powder (e.g. alumina) spread on glass/plastic plate (stationary phase)
qualitative analysis = indicate which chemicals present but not concentration
interpret = including standards of known chemicals on chromatogram as sample, calculate retardation factor (Rf) of sample
standards: need idea of chemicals present
sample and standards on same chromatogram b/c distance from origin depends on distance solvent front (movement of solvent)
Rf = distance component travels from origin / distance solvent front travels from origin
component most strongly adsorbed onto S.P = shortest distance = lowest Rf
reversed-phase HPLC = stationary phase = silica (non-polar) & polar solvent as m.p (e.g. water/ methaol)
polar molecules = strong hydrogen bonds / dipole-dipole w/ solvent molecules = weakly adsorbed onto S.P
non-polar compounds = adsorb onto non-polar S.P = dispersion forces = less soluble in solvent = can't form hydrogen bonds
retention time (Rt) = time taken for component to pass through column
identify components w/ peaks (quantitative analysis)
component identified by adding known compound to sample (spiking)