Connect the column in reverse:

• Attach the outlet end of the column to the pump tubing (normally connected to the inlet).
• Direct the new outlet (original inlet) to waste, not to the detector.

Reason: Back‑flushing dislodges material trapped on the inlet frit, especially particulates. Sending this material through the detector line risks clogging, contamination, or cell damage.

Reminder: Flow reversal is standard practice for cleaning but should never be used during analytical runs.

2. Select the Appropriate Wash Solvent

Your choice of solvent depends heavily on the type of contamination:

A. Particulate Contamination

• Any solvent is acceptable.
• The key is higher flow rate, which provides the mechanical force needed to push particulates out of the frit.

B. Chemical Contaminants

Evaluate contamination based on your chromatographic mode:

• Reversed‑phase contaminants (hydrophobic carryover):
  • Use 100% acetonitrile to aggressively remove strongly hydrophobic residues.
• Diamond Hydride™ or ANP‑mode contamination (polar/ionizable residues):
  • Use 50:50 DI water/methanol or 50:50 DI water/isopropanol.
• These blends effectively dissolve a broad spectrum of hydrophilic and moderately hydrophobic contaminants adsorbed to TYPE‑C silica surfaces.

Tip: The 50:50 mixtures also re‑hydrate TYPE‑C surfaces effectively, helping restore ANP performance after contamination.

3. Wash Out the Contaminants

Chemical Contaminants

• Use a low flow rate and flush the column overnight.
• Slow, extended washing allows deeper penetration into the pore structure and desorption of strongly bound residues.

Particulates

• Use higher flow rates, as the mechanical force helps dislodge particles embedded in the frit.

Do not exceed column pressure limits. TYPE‑C columns can be robust, but excessive force may damage the packed bed.

4. Return the Column to Normal Operation

After cleaning:

• Reconnect the column in the correct (forward) direction.
• Equilibrate with your intended mobile phase until stable baseline and pressure are reached.
• Test performance using your method.

How to interpret results:

• High backpressure → likely remaining particulate contamination.
• Ghost peaks or retention changes → chemical contaminants still present; consider a stronger or longer wash.

Additional Best‑Practice Notes

A. When to Perform Back‑Flushing

• Sudden or progressive pressure increases
• New ghost peaks
• Peak distortion or retention shifts
• After runs with complex matrices, environmental samples, or biological extracts

B. Back‑Flushing and ANP Mode

Diamond Hydride™ columns benefit from balanced hydration, so after back‑flush cleaning, always re‑establish ANP conditions with:

• High‑organic starting composition (e.g., 90–95% ACN)
• Consistent additive system (FA, acetic acid, or ammonium acetate)

Summary:

Back‑flushing is a safe, effective procedure for restoring Cogent TYPE‑C™ columns. Reverse the flow, select the correct solvent depending on contamination type, clean with the appropriate flow rate, and re‑equilibrate before reuse. These steps help eliminate pressure problems, restore retention, and extend the lifetime of Diamond Hydride™ and other TYPE‑C columns.