I'd recommend you to do a Master dilution, just in case you have to repeat the PCR. Moreover, in this way you diminish the risk of lysing your DNA template due to excessive freeze-thawing cycles. Lets suppose your final reaction volume is 10 uL (2uL for primers, 7uL of Master mix and 1 uL of template DNA). To prepare a 20 uL (25 ng/uL) solution, so you'd just add 1 uL, do as follows:
C1V1 = C2V2
Where:
C1: concentration 1
V1: volume 1
C2: concentration 2 (desired concentration)
V2: volume 2
V1 = (C2V2)/C1
V1 = [(25)(20)]/230
V1= ~ 2.174 uL
20 uL (H2O) - 2.174 uL (template DNA) =17.826 uL
This means you need to add 2.174 uL of template DÑA, for every 17.726 uL of H2O to get 20 uL of solution with a concentration of ~25.001 ng/mL.
According to final volume of pcr reaction.. it is better to dilute your sample 1:10 to reach a concentration of 23 ng/ul supposing you are sure of your concentration.. then if the total volume is 50 ul you will use the equation c1v1 = c2v2
I'd recommend you to do a Master dilution, just in case you have to repeat the PCR. Moreover, in this way you diminish the risk of lysing your DNA template due to excessive freeze-thawing cycles. Lets suppose your final reaction volume is 10 uL (2uL for primers, 7uL of Master mix and 1 uL of template DNA). To prepare a 20 uL (25 ng/uL) solution, so you'd just add 1 uL, do as follows:
C1V1 = C2V2
Where:
C1: concentration 1
V1: volume 1
C2: concentration 2 (desired concentration)
V2: volume 2
V1 = (C2V2)/C1
V1 = [(25)(20)]/230
V1= ~ 2.174 uL
20 uL (H2O) - 2.174 uL (template DNA) =17.826 uL
This means you need to add 2.174 uL of template DÑA, for every 17.726 uL of H2O to get 20 uL of solution with a concentration of ~25.001 ng/mL.
Dear colleagues I agree with your suggestions. But I would like to add something. First of all is it conventional PCR or Real time? May be for the purposes of NGS? Please be carefull with concentration. Use fluorimetry-based approaches to quantify DNA more precisely.