Analysis of Short Amines without Using Ion Pair Reagent
For the HPLC analysis of basic compounds such as short amines, ion exchange columns
or ODS columns with an ion pair reagent are commonly used. However, for the analysis
using ODS columns with an ion pair reagent, it is problematic to control the separation
because the following two modes contribute to the separation.
1) Mode 1
With this mode, the sample and the ion pair reagent generate an ion pair
compound, and at the same time, the sample hydrophobicity increases due to
the presence of an alkyl chain coming from the ion pair reagent. Therefore
the sample is retained by the column.
(+) + ion pair reagent(-) = [R-NH3
(+)(-) ion pair reagent]
2) Mode 2
With this mode, the ODS column works as an ion exchange column. The strongly
hydrophobic alkyl chain coming from the ion pair reagent is adsorbed by the
Compared with ODS columns, polymer-based reversed phase ODP2 HP
, Asahipak ODP
and RSpak DE
have the following advantages:
a) Reversed phase analysis of short amines can be performed with an eluent at
pH10-11 without using an ion pair reagent.
b) Under alkaline conditions, the peak shapes of short amines are very
c) ODP and DE columns are stable over a wide pH range from pH2 to pH11.