Hi, I hope you maybe can explain something from the following:
Whole Blood collected in EDTA vials have been sent for DNA extraction with a commercial genomic DNA kit and through an automated extraction device from the same company. The the 260/280 ratio was absolutely fine but unfortunately for the majority of the samples the 260/230 ratio was between 1,9 to 1,4
The kit contained among other Rrnase A, Proteinase K, Lytic buffer, Lytic Enhancer. Also the method for DNA extraction was from paramagnetic beads. The kit is indicated to be stored at room temperature
The used kit was 6 months expired, does this have an effect?
1. *Typically* absorbance at 230 is leftover chaotropic salts from one of the earlier steps. Since 260/230 is roughly a ratio of DNA absorbance to the absorbance of one of these salts. So without knowing the concentration of each sample, it could simply be that the 1.4 sample has a lower DNA concentration than the 1.9 sample, but each sample could have the same absolute amount of leftover salt.
2. Sometimes samples with roughly the same concentration of DNA can have very different 260/230 ratios, Usually this means that for whatever reason the salt removal wash steps were not as effective on the samples with the lower ratios. That's why I use more than the recommended number of desalting wash steps with longer incubation periods in an effort to mitigate that.
3. There's also other factors like some samples containing a higher number of contaminating molecules which absorb at 230 than others (in your case that could be differences between samples or the way they were handled before purification).
I'm going to guess it's more likely effected one of those three things than the kit being expired by less than a year.
Try adding an additional wash step after dna binding to make sure that all of the chaotrophic salts have been removed before eluting the dna. Using too much initial sample can also cause this effect
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