Negative 260/230 Ratios in Nano Drop???

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Tom_Brassica
Tom_Brassica's picture
Negative 260/230 Ratios in Nano Drop???

 I am attempting to extract DNA from roots infected with a pathogen (so I want DNA from both the host and pathogen). I followed the Qiagen mini kit and checked the DNA quality of the DNA extracted with Nanodrop.

My 260/280 ratios are really nice, 2.0-2.2.
My 260/230 is negative, -0.1 to -11.
Concentrations range 8 to 15 ng/uL

I attempted a DNA extraction from some pathogen isolated and cleaned spores using the Qiagen maxi kit. I got similar results, good 280 ratio, negative 230 ratio, 9 ng/uL.

I believe the Nanodrop is working fine because my colleague got perfect Nanodrop results for an RNA extraction I assisted him in. We have no idea what the negative ratio could mean.

Tom_Brassica
Tom_Brassica's picture
 Update: For the second

 Update: For the second extraction mentioned, I incubated the extraction for 2 hours at room temperature and checked with Nanodrop again. The results for concentration and 280 ratio were the same. The 230 ratio changed from negative to positive 24.

Sami Tuomivaara
Sami Tuomivaara's picture
Tom_Brassica,

Tom_Brassica,

If the blank solution has a contaminant (absent or at lower concentration in your sample) that absorbs at 230 nm (and not at all or little at 260 or 280 nm), it could explain the problem. What are the individual absorbances at 230, 260 and 280 nm, knowing that would help in troubleshooting!

Cheers,

nmoehn
nmoehn's picture
 I work in a lab and we

 I work in a lab and we recently did nanodrops as well. We did a large number of them (around 200) and about half of them were within your range of density (1-18 ng/ul). These samples all had either negative 260/230 values or had a very large value (at least 20). I think it might have to do with the accuracy of the machine at low density but I'm not sure

dav668
dav668's picture
 Hi,

 Hi,

Could it be due to TE which may absorp at 230? saw this piece of info somewhere in this forum.

Dav