How does DNA normalization work?

Each library preparation used in a multiplexed DNA sequencing run varies in content as well as concentration. The quality and quantity of the starting sample and the efficiency of the DNA extraction protocol are important factors that impact the final concentration. Using DNA normalization to even out these libraries helps generate NGS data that is consistent and reliable. 

Normalization can be carried out at various stages in a multiplexed sequencing workflow. You may normalize the size distribution of library fragments, concentration of input DNA, and the concentration of library prep prior to pooling.

Checking the concentration of library preps can directly impact clonal amplification, clustering efficiency, and read uniformity across the pooled libraries. Consequently, quantitatively checking individual library preps and adjusting them to equimolar ratios before pooling are considered standard protocols. This step ensures that all libraries are equally represented on the flow cell.