This PQRI approach is established based on a hydrophobic subtraction
mode for reversed phase column selectivity [20–23]. Other
studies also demonstrated the significant molecular shape selectivity
of PFP column [24,25]. These interactions are also influenced by
the mobile phase properties, and as illustrated in Fig. 3, methanol
is a better organic mobile phase compared to acetonitrile for the
separation of these isomers in addition to its lower cost, possibly
because methanol is a polar protic solvent, which can form hydrogen
bonding with phenolic compounds, while acetonitrile is a polar
aprotic solvent that cannot form hydrogen bonding. But acetonitrile
has dipole–dipole interactions with these compounds.
To further increase separation efficiency (N) and reduce solvent
consumption and analysis time, shorter analytical columns
with smaller particle size were used in the new HPLC method.
Compared to the HC HPLC methods [11,12], which use three different
mobile phases and therefore need a expensive quaternary
pump system for mobile phase delivery, the new method uses
two simpler mobile phases, which are much easier to prepare and
can be delivered by a less expensive binary pump. As shown in