Dear colleagues,

I have a dissolution method (n=6 vessels) generating profiles at 7 times points with typical values around 100% within 10minutes.
The HPLC method is isocratic.

Erratically, one injection delivers high results i.e above 120% or more. As the previous and next time points, as well as the other vessels deliver consistent results around 100%, I exclude an issue with the sample.
Besides, re-injection of the HPLC vial delivers consistent results around 100%, therefore I tend to exclude an issue with the sample vial.

What could be the cause of the erratic higher values? I lean toward residues at the column head or injector due to improper needle wash or other residues.
Any on how to investigate and solve it? As the issue is very erratic, one of the difficulty will be to reproduce the issue at will.

Thanks!