There is little or no library peak when assayed with a fragment analyzer.

Possibilities include:

• Using incompatible index primers.
• DNA quantification was inaccurate, especially if using spectrophotometric methods such as nanodrop, OR DNA quality is extremely poor.
• 30% ethanol instead of 70% ethanol OR using TE/H2O instead of 70% ethanol was used in DNA purification.
• Forgetting to add magnetic beads for any of the purification steps.
• Forgetting to add one or both index primers in the 2nd PCR step.
• Over-digestion, forgetting to add Stop Buffer after digestion, or pausing after digestion step.
• Weak or incompatible magnetic rack. Do not use racks designed for 1.5 ml tube.