I am trying to produce and purify plasmids from competent cells for transfections however i keep attaining low quantities of around 80-120ng/ul.
I am following a set protocol and purification using QIAprep minprep kit.
I am culturing my competent bacteria (which have been previously transfected with the selected plasmid) overnight in 0.1% Ampicillin at 37C and at 220 rotations per minute.
Edit: Now a year on I have came back to this question and understand 0.1% of Ampicillin is not a great way to communicate concentrations. We are using miniprep kits so understandably this is why i received lower concentrations than what i was hoping. Thank you for all your answers!
The yield seems perfectly fine especially if it is an expression vector (then most likely it has pBR322 origin) if you are eluting with 50ul buffer or water that should be giving you a total of 4-6ug of plasmid, which is more that enough for most downstream applications. This yield might be low if your using a plasmid with high copy number origin (like pUC19 ori), however, this is also dependent on other factors like the size of the plasmid and how much you grew the cells and whether the plasmid is toxic etc..
A side note is that the antibiotic concentration is better expressed as x ug/ml (you most likely used 1ul per ml of media of 100mg/ml amp stock or 50mg/ml amp stock both of which would be fine) however if your stock concentration is lower than that you might not be selecting for cell harboring the plasmids anymore thus reduced yields. To better answer this question please add the following:
1-volume of overnight culture
2-origin of replication in the plasmid
3-concentration of your amp stock
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