When I measure the Dna concentration for 2 samples
The firest sample reading was all negative value abs 260- 1.4 abs 280-0.006 260/280 eas also negative -.44
While dna amount was -1.4
The second sample was also have negative reading at 280 but the dna amount was 9microgram/ microliter
What is wrong ?
the usual reason is that the blanking ( zeroing) of nanodrops must be done with exactly the same solvent at the same concentration and pH as that used in dissolving the DNA. If you blank with TE and dissolve the dna in water then you may get negative results. Protein and dna sticking to the optical lenses of the nanodrop can also cause odd results and the remedy is to clean the lenses with HCl as recommended in the manual. Samples should also be measured quickly as the small sample size allows quick evaporation and absorption of CO2 from the air if left too long before measurement
Does a fault during extraction can cause this problem? I mean if the sample has no dna at all what are the possibities of the results
A fault during DNA extraction could result in no DNA that was isolated. If this were true, then you would get a reading of 0 but not negative. I agree with Paul Rutland that you are probably having a problem with your blanks or with the instrument or your buffers.
Dr.Paul and Dr. Michael, thanks you both In deed when I changed the blank ,l got a DNA reading.
May be your baseline solution has some contamination or not the same solution which you dissolve your DNA on it (DW or TE for example) or your sample has some contamination.
As a solution, Try to make ethanol precipitation for your DNA samples and try to insure you didn't lose your DNA by loading some in Agrose gel and check concentration by comparing to known concentration.
I agree with Paul. The blanking is crucial to getting usable data. I have even experienced blanking with the same buffer from the same company, but it was from a different lot number and resulted in negative values. For extractions where elutions are in a buffer other than pure water, I require that the buffer used be written in the lab notebook and the last few ounces of a buffer container be put aside for blanking.
Another possibility is alcohol, phenol, or other carryover from sample preparation. The curves will look odd with a peak too early or too late. Examples of these curves can be found with by googling Nanodrop troubleshooting. Hope that helps. Good luck!
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