Dear all,

I have a RP-HPLC method, gradient (acetate at unbufferd pH/ acn) over about 20 min, with UV detection which is used for the quantification of degration products in a commercial Drug Product.
- The diluent in ACN/HCl; and we are not using the capsule shell for the sampes.
- Two replicates as performed. The composites are dispersed in diluent, sonicated, and filtered through nylon syringe filter
- - During the last analysis, one of the duplicate had a bump which looks like a complex mixture of analytes which comes out at about 4 min.
- This bump is slighly observed in diluent and all injections but at much lower level (diluent is filtered too for diluent injections)
- The incriminated sample was at the middle of the run, with no issue on previous or later samples.
- No impurities is known at this RT from our product knowledge.
- we injected diluent from a number of vials trying to inspect vial cleaningless, but it did not reproduce the hump

This is the 3rd occurence in 6 months, hence vial contamination is possible but unlikely since it would mean that the same contamination occured 3 tines in 6 months.

We performed confirmatory testing of the failed vial/flask on a different HPLC: the vial still did show the same bump, but a re-vialed sample from the flask did not.
Hence, we can exclude an instrumental issue; and it seems rather to point towards the filtration or vialing process. All samples were filtered and vialed using the sames batches of consumables, hence we cannot explain the issue on this particular vial at the moment, and the problem seems difficult to reproduce willingly.

Any suggestion?
Thanks !