Purity of eluted gDNA samples is assessed by reviewing OD ratios collected during routine spectrophotometry. Pure gDNA typically has an A260/280 of 1.8–1.9 and an A260/230 of 1.8–2.5.
The integrity of the gDNA is assessed by loading approximately 100 ng per sample on a 0.75% agarose gel and comparing size distribution to a suitable marker, such as lambda DNA, either as full length DNA (NEB #N3011) or digested with HindIII (NEB #N3012). Typically, for intact gDNA, the majority of the gDNA signal will be larger than the upper band of the HindIII digest. Alternatively, gDNA samples can be run on an Agilent TapeStation® using a Genomic DNA ScreenTape. This system will provide information on the peak size of the gDNA and the overall integrity via the DIN (DNA Integrity Number). High peak sizes (>50 kb) and DINs >8.5 indicate that the DNA is of high quality.
For more information on assessing nucleic acid purity, download our application note, A Practical Guide to Analyzing Nucleic Acid Concentration and Purity with Microvolume Spectrophotometers.