Hey everyone — looking for some advice on a column fouling issue.
I’m running an RP-HPLC assay on an Ascentis Express C18 (15 cm × 4.6 mm) for an API (MK-8507) that’s spray-dried in HPMCAS. Mobile phase is 0.1% orthophosphoric acid (A) and ACN (B) with a ~29 min gradient.
I keep getting a persistent interference peak right at ~13 min — basically co-eluting with my API. Full spectra matches closely, and the peak sticks around no matter what I do. I’ve already tried flushing the column (forward flow) with:
- ACN
- IPA
- Acetone
None of that removed it.
At this point I’m thinking it’s not API carryover but polymer (HPMCAS) fouling — possibly depositing on the column and eluting in the same hydrophobic window.
I haven’t tried backflushing yet, and I’m considering:
- Backflush with IPA
- Or going straight to THF (with proper water/ACN flush steps first)
Constraints:
- Method is validated, so I can’t change mobile phase or gradient
- Only looking to add a cleaning/maintenance step
- No guard column currently (might propose one)
Questions:
- Does this sound like polymer fouling to you?
- Would you try IPA backflush first, or go straight to THF?
- Any experience with HPMCAS specifically sticking to C18?
- Any other cleaning approaches that have worked for you in similar cases?
Appreciate any insight — this one’s been stubborn.