NPC and RPC Flashcards
What do we mean by the term bonded phases?
covalent attachment of functional groups to the silica surface
Why is it not possible for all silanol groups on silica surface to react with functional groups?
there are steric considerations
What can be done to prevent peak tailing due to non-bonded silanol groups?
a process known as endcapping
What is endcapping?
cover more silanol groups with di- and tri- chlorosilane reagent
What is the effect of carbon loading on retention times?
higher the carbon loading, more non-polar the SP becomes and more retention for hydrophobic compounds
What are the advantages of polymeric C-18 RP columns over the silica-based C-18 columns?
wider operating pH range, with no peak tailing
What are the disadvantages of polymeric C-18 columns?
longer retention times if hydrobic polymer is used and swell with organic solvents
What is the major reason for functional group usage?
in order to produce changes in selectivity rather than retention
What type of separation is NPC best suited for?
solutes that are soluble in in non-polar solvents
isomers
molecules with different functional groups
Why is RPC more commonly used over NPC?
allows for greater separation
more choice of columns
MP choice requires careful consideration in NPC
What is RPC best suited for?
separation of neutral solutes that are soluble in water or relatively polar solvents
Selectivity values are generally _______ in RPC for homologs, and benzologs, but not isomers.
higher
What is isocratic method?
constant composition of MP mixture
What is gradient elution?
altering the composition of two or more solvents in MP during HPLC run
When is gradient elution used?
when a mixture of solutes with a wide retention factor range is to be separated
