Formula to convert from ng/ml to nM

Question

[Amr]

Some standard Illumina libraries, such as Nextera, require the use of dsDNA-specific fluorescent dye methods for accurate quantification. These methods typically measure dsDNA concentration in ng/µl. To convert from ng/µl to nM for cluster generation, follow the instructions below. 1. Determine the average size of the library by running it on an Agilent Technologies 2100 Bioanalyzer. 2. Use the following formula to convert from ng/μl to nM:

      ( Concentration in ng/μl )
  _______________________________  X 10^6 = concentration in nM             
  ( 660 g/mol x average library size in bp )

Excuse me, I don't understand why we multiply in 660 and why 10^6 specifically?

Thanks in advance

[GenoMax]

The 660 g/mol value is the mean mass of the sodium salt of DNA (paper)

The mean (659.841 ± 0.003) g/mol value of the “Na+ Salt” in Table 3 is for equal proportions of AT and GC pairs. AT pairs typically outnumber GC pairs in a ratio of 60-to-40 [29]. The (659.743 ± 0.003) g/mol of the 60:40 weighted mean is a more appropriate estimate for genomic DNA.

[Amr]

Thanks a lot GenoMax for your help :)

Answer 1

[Joe]

660 is approximately the average mass of a single base pair. In order to convert from a mass/volume (concentration) to a molarity, you need to use the g/mol of the molecule in question.

Multiplying by 10^6 is just to get back to the right order of magnitude (nanomolar) since you've just converted in grams per mol

You might want to look at a site like https://nebiocalculator.neb.com/#!/dsdnaamt to help you understand.

[Amr]

Thanks a lot Joe for your help :)