Analysis of Isomers of Phenylenediamine on Zodiac HST OG Column

Lets explore the capabilities of Zodiac HST OG Column in separation of the positional isomers of ortho, meta , and para Phenylenediamine,

Zodiac HST OG with an innovation chemistry can offers a mixed-mode separation mechanism combining reversed-phase, cation-exchange interactions and Ion exclusion mechanisms

Why this order ?

1. o-Phenylenediamine (ortho) – Least basic (pKa ~4.5)
* The two -NH₂ groups are next to each other.
* They form strong intramolecular hydrogen bonds, which reduces their ability to interact with the stationary phase.
* Less retention → elutes first

2. m-Phenylenediamine (meta) – Intermediate basic (pKa ~5.0)
* The -NH₂ groups are further apart, no intramolecular H-bonding.
* Moderate interaction with stationary phase → moderate retention

3. p-Phenylenediamine (para) – Most basic (pKa ~6.0),
* NH₂ groups are opposite each other → symmetry allows stronger, more stable interaction with stationary phase.
* Both groups are fully available for interaction (especially ion-exchange).
* Strongest retention → elutes last