When working with Cogent Diamond Hydride™ TYPE‑C Silica™ columns, analysts sometimes ask whether ion‑pairing reagents can be used to enhance retention of ionic analytes. The short and definitive answer is no: Ion‑pairing is not compatible with Diamond Hydride™ columns. 

Why Ion‑Pairing Does Not Work with the Diamond Hydride™ Stationary Phase

Cogent Diamond Hydride™ columns operate fundamentally on polarity‑based separation mechanisms, dominated by Aqueous Normal Phase (ANP) behavior along with tunable interactions that also enable Reversed‑Phase‑like retention for certain analytes. The core mechanism is dependent on maintaining the native polarity of solutes in the mobile phase environment.

Ion‑pairing reagents, however, chemically alter analytes by forming neutral or less‑polar ion pairs. This effectively reduces the analyte’s polarity, shifting its chromatographic behavior away from ANP mechanisms. Once polarity is suppressed, the analyte behaves more like a typical hydrophobic species better suited for conventional Reversed Phase chromatography. Because Cogent Diamond Hydride™ columns derive their unique selectivity from polarity‑driven interactions at the silica‑hydride surface, ion‑pairing disrupts these mechanisms and produces poor or inconsistent retention.

What Happens If Ion‑Pairing Reagents Are Used

If ion‑pairing reagents are introduced into a method while using a Diamond Hydride™ column, analysts may observe:

• Loss of retention (analytes eluting too quickly or near void volume)
• Greatly reduced selectivity, especially for ionic or zwitterionic molecules
• Unpredictable peak shapes due to partial pairing or altered partitioning behavior
• Potential surface contamination, since many ion‑pairing reagents strongly adsorb to silica surfaces

These outcomes are consistent with compatibility issues reported in practice and noted in the source documentation.

Recommended Alternatives to Ion‑Pairing

Instead of ion‑pairing, consider the following approaches, which preserve the polarity‑based separation benefits unique to Diamond Hydride™ columns:

1. Adjust aqueous content of the mobile phase to modulate ANP behavior.
2. Optimize acid modifiers (e.g., formic or acetic acid) to improve ionization and reproducibility.
3. Explore pH effects, as analyte ionization state strongly influences ANP retention.
4. Use volatile buffers appropriate for LC‑MS to maintain clean ion source conditions.

These strategies maintain compatibility with TYPE‑C Silica™ chemistry and avoid the suppression of polarity caused by ion‑pair reagents.

When Ion‑Pairing Should Be Used Instead

If the analytical goal genuinely requires ion‑pairing—for example:

• Permanent retention of highly ionic quaternary amines
• Strongly hydrophilic analytes with no ANP or RP retention
• Methods that rely on fixed ion‑pair equilibrium

—then analysts should select a conventional Reversed Phase column, not a Cogent Diamond Hydride™ column.