The example below shows the presence of a sharp peak around 150 bp due to the presence of adapter dimers. For Singular Genomics adapters, sizes for adapter dimers range from about 125 bp for non-indexed adapters to about 151 bp for indexed adapters.

Generally, adapter dimers may be present for one or more of the following reasons:

The size selection conditions were not stringent enough to remove the dimers.

The size selection may have failed or was inefficient.

The ligation conditions were not optimal, for example, low input or excessively high adapter to insert ratio.

If your library looks like the one below, consider an additional size selection using a lower ratio of beads to sample prior to sequencing.

Figure 1 Example of a trace with adapter dimers. Peaks at 35 and 10380 bp are size markers.