Hello everyone,

Recently, I performed the procedure of synthesizing DNA libraries for NGS (Ion Torrent platform, ThermoFisher). I performed the procedure as usual, according to the manufacturer's recommendations and I had never had such a situation before. In the attachment I am sending the results from the Agilent Bioanalyzer High Sensitivity DNA Assay.

What could it be?

It's true that the gel was 2 weeks after the expiry date, but I filtered it again, but the ladder did not come apart properly, it is more "squeezed" (file). Anyway, I repeated the experiment, cleaned the 4 libraries on the magnetic beads again and synthesized 2 other libraries (in the attachment). The two new libraries look OK. But the previous ones still don't.

I don't understand what happened. Why has the contamination not decreased despite cleaning on magnetic beads?

Does anyone have an idea why this happened?