Chromatographic behaviour of synthetic high pressure high temperature diamond in aqueous normal phase chromatography

- Non-porous irregular synthetic diamond particles are used in aqueous normal phase chromatography.
- Retention mechanism in acetonitrile and methanol based mobile phases is established.
- Various buffers effects on the separation selectivity are tested, including alkaline eluents.
- A unique selectivity reversal is observed with change acetonitrile/methanol ratio in the eluent.
- Weak cation-exchanger could be useful type of phases for aqueous normal phase chromatography.

The chromatographic properties of high pressure high temperature synthesised diamond (HPHT) are investigated under the conditions of hydrophilic interaction liquid chromatography (HILIC). A 50 × 4.6 mm ID stainless steel column packed with HPHT particles of mean diameter 1.6 μm and specific surface area 5.1 m2 g−1 is used. According to the results of acid-base titration with NaOH the purified HPHT batch contains 4.59 μeq g−1 of protogenic, mainly carboxyl- and hydroxyl-, groups, which make this polar adsorbent suitable for use as a stationary phase in HILIC. The retention behaviour of several classes of polar compounds including benzoic and benzenesulfonic acids, nitro- and chlorophenols, various organic bases, and quaternary ammonium compounds are studied using acetonitrile and methanol based mobile phases containing 5-30 v/v% of water. The effects of the buffer pH and concentration, column temperature and organic solvent content on retention of model compounds are also investigated. It is shown that both pH and acetonitrile/methanol ratio in the mobile phase can be used to vary the separation selectivity. Molecular adsorption mechanism (related to aqueous normal phase mode), rather than partitioning is established to be responsible for the retention.