ColumnSelection
Because highly charged paraquat and diquat are poorly retained on analkyl
stationary phase, any standard reversed phaseHPLC technique that relies solely
on the hydrophobicity of the column and the strength of themobilephase likelywill
fail to achieve a separation. If changing the hydrophobicity of the stationary phase is
ineffective, the next choice is to lower the relative hydrophilicity of themobile phase.
Wehave developed a simple, effective analysis for paraquat and diquat, based on a
newHPLC column and a uniquemobile phase. This analysis can be performed on
a conventional HPLC system using aUV detector.
The separationmakes use of a different analytical property – chaotropism: an ability
to disrupt the ability of water to solvate ions and thereby alter the charged
interactions among the analyte, themobile phase, and the stationary phase. In this
case, by dispersing the analyte’s charge, the solubility of the highly polar analyte
upon a non-polar substrate (the stationary phase) canbebe enhanced. The
analyte’s retention is then enhanced because it remains longer upon the absorbed
solvent layer (acetonitrile) present on the stationary phase.
The packing for the new column ismanufactured from typeB silica, to ensure
proper selectivity and analyte retention, and tominimize interactions between the
analytes and residual silanols andmetal ions on the packing particles, which can
lead to tailing and unwanted / unpredictable retention.
