DNA library after size select has 2 peaks

[Ekaterina_Marnat]

Hello!
After the Ampure XP beads magnetic beads selection, the libraries have 2 peaks (Pic.1), but this did not happen before and they looked normal (Pic.2). The reagents were not changed, what could be the reason? Fragmentation by Covaris.

[fchatonnet]

Hello,

you also have a very long "tail" of high size fragments in Pic. 1, so I would think that your SPRI bead selection didn't work well this time.
Maybe you didn't apply the good beads:sample volume ratio, or the beads are a bit old?
Do you let them stabilize at room temperature for 30' before using them, as recommended?
Is it a new bottle / new lot of beads? We used to qualify the beads for each lot since the results of a fixed ratio on the selected size can vary a lot from different beads bottles...
Another explanation could be that the selected product had a different profile than usual and was enriched in high size fragments, so the purification is not complete?

Good luck!