Accidentally allowing air to enter an HPLC column—especially a Cogent Diamond Hydride™ (TYPE‑C Silica) column—can temporarily disrupt retention, efficiency, and peak shape.

Although the column should not be allowed to dry, the good news is that columns exposed to air are typically not permanently damaged and can be restored with proper re‑conditioning. 

1. What Happens When Air Enters a Diamond Hydride™ Column

When the mobile phase runs dry, air pockets can form within the packed bed. This can cause:

• Loss of retention
• Erratic peak shapes
• Increased column noise or drift
• Poor reproducibility

These symptoms occur because TYPE‑C silica requires a properly wetted surface to establish its mixed‑mode ANP/RP retention mechanisms.

2. First Step: Slowly Remove Entrapped Air

To safely purge the column:

Option A — Purge with Mobile Phase

• Run the column at a low flow rate (≈ 0.1–0.2 mL/min)
• Continue for several hours
• Increase flow rate only after stable pressure is observed

Option B — Use Isopropanol (IPA) to Displace Air

IPA has excellent wetting properties and can help displace trapped bubbles faster.

• Flush with IPA at a slow flow rate for 1–2 hours
• Follow with the mobile phase to return the column to normal operation

Do NOT use high pressure or fast flow during recovery—this can damage the bed while internal pockets are still decompressing.

3. Re‑Condition the Column Properly

After air removal, you must fully reset the column surface:

Follow the conditioning instructions included with the column, typically:

• Flush overnight at low flow with a 50:50 aqueous/organic mixture (commonly MeOH/DI water).
• Then equilibrate the column in your actual mobile phase for at least 30 minutes.

4. If Retention Is Still Low: Check Method Conditions

Low retention after re‑conditioning is often NOT column damage, but instead a method setup issue. Confirm the following:

A. You are NOT starting at “100% A”

Starting at 100% A is equivalent to starting in pure aqueous, which suppresses ANP retention and forces the separation into reversed‑phase mode.

• Hydrophilic analytes will not retain under RP conditions.

B. Ensure Analytes Are Ionized Before Injection

Retention of polar/ionizable compounds in ANP depends heavily on correct charge state.

• Confirm that Solvent A contains acid or base (within the pH limits of TYPE‑C silica).
• Solvent B should be acetonitrile with 5% DI water and the same acid/base as Solvent A.

Ionization mismatch can produce:

• Poor retention
• Peak distortion
• Non‑reproducible chromatography

C. Verify Mobile Phase pH Is Within Column Range

TYPE‑C silica generally supports pH 2.5–7.5. Exceeding that range can reduce performance or damage the silica surface.

5. Practical Tips to Prevent Air Exposure in the Future

• Always keep reservoir levels high enough for unattended runs.
• Install a mobile phase level sensor or use bottle caps with dip‑tube extensions to avoid sudden emptying.
• Prime solvent lines after every solvent change.
• Before starting each sequence, verify stable pressure and a bubble‑free baseline.

Summary

Even though air should never enter an HPLC column, accidental exposure typically does not permanently damage a Cogent Diamond Hydride™ column. Restore it by purging air at low flow, optionally flushing with IPA, and reconditioning with the appropriate aqueous/organic mixture. If retention remains low, confirm that your method is not inadvertently running in RP mode, that your analytes are correctly ionized, and that your mobile phase follows TYPE‑C silica requirements.