| | Re: why are some dilutions of std curve detectble and some not?
First important question is whether you used exactly the same dilutions or freshly made dilutions?
In the first case, if you freeze-stored your dilutions, there is a chance that some of the DNA degraded and this might have caused decrease in your DNA concentration.
With very low DNA copy number one or several of the replicates for one dilution might give negative results. The lower the copy number the higher the probability of obtaining such results.
If you prepared your dilutions just before the assay and obtained such results this may be caused by uneven dilution of your samples. It may be difficult to get identical DNA concentrations in all replicates if you have low concentration of your DNA in a certain dilution.
To make dilutions it is recommended to use rather larger volumes, if possible. So instead of making ten-fold dilution by adding 1ul of a sample to 9ul of buffer or water add 5ul to 45ul.
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