This video walks you through the size selection and cleanup steps using the NEBNext Ultra II DNA Library Prep Kit with Sample Purification Beads. Find the manual for this kit at www.neb.com/~/...
Following the Ultra II Library Prep protocol you typically come out of adaptor ligation with 96,5µl. Selecting for 400-500bp I understand why the bead to sample ratio is so low (~0,25X). But after binding of large fragments to the beads you withdraw the whole sup again (96,5) and then use only 10µl of beads, meaning an even lower ratio, is that correct?