eDNA - Standardizing qPCR and ddPCR outputs

It is essential to standardize the amount of DNA measured in a single qPCR reaction to the amount of water filtered in the field. To do this it is not as simple as just dividing the quantity of DNA in the qPCR reaction by the volume filtered.  

In each case, qPCR or ddPCR, copies per PCR reaction is estimated and then converted to copies per unit of sample (e.g. litre) using information like the volume of water filtered, the volume of DNA extracted, and the volume of DNA used in the PCR reaction. For example, for a filtered water eDNA sample:

CopiesSample =CopiesPCR Volume (uL) of PCR reaction Volume (uL) of template DNA in PCR reaction Volume  (uL) of DNA extractVolume (L) of Water Filtered

Where CopiesSample = the concentration of DNA or copies of your target gene per volume (e.g. litres) of sample collected. Where CopiesPCR = the concentration of DNA or copies of your target gene in your PCR reaction. This is the value you calculate from the Cq value of that sample and your qPCR standard curve or the concentration value that is calculated by the ddPCR machine.