The principle of SPR is based on the reaction
between the fatty components in the traces and the
hydrophobic tails of each specific reagent. These tails
are linked to the hydrophilic heads which react with
metal salt to give a precipitate.(1) Choline chloride is
one such water soluble organic compound with a
hydrophilic cation with the chloride anion, and
a hydrophobic tail. Thus, the presence of choline
chloride in SPR II may help to enhance the
effectiveness of this formula by giving more
attachment sites between the metal salt and the
hydrophilic head based upon its polar property.