Hi guys. Here is the problem:

Using an SpectraMax Microplate Reader for DNA absorbance test, there is one problem that the A260/A280 is always wrong, sometimes half plate wrong and sometime, several lanes. The acceptance criteria is 1.8-2.1,however we received below 1.8 and above 2.1.Testing the samples again using Nanodrop, all went good and the concentration is quite similar. Really wondering that why the ratio is not good.

Here is some details about my experiments:

UV plate is from Corning.

I transfer 10ul sample first and 190ul distilled water next.

I use the 8-row pipette to mix well and also 10sec vigous shaking on the machine (if manual mixing is not present, the results is even worse)

The samples I wanted to test was mesenchymal stem cell-treated mice' DNA.

Is there any idea?