Do you have a protocol for the removal of endotoxins from already purified plasmid DNA?

Yes. Endotoxins can be removed from purified plasmid preparations by following the Supplementary Protocol 'Removal of endotoxins from purified plasmid DNA using the EndoFree Plasmid Maxi Kit' (QP12).

This protocol requires the EndoFree Plasmid Buffer Set, which can be purchased separately. Alternatively, the EndoFree Plasmid Maxi Kit, containing all necessary components, can be used.

The plasmid DNA is first treated with endotoxin removal buffer ER, and then applied to QIAGEN's anion-exchange tip. After performing a wash step, the plasmid DNA is eluted from the tip, followed by isopropanol precipitation and redissolving the DNA in a suitable volume of endotoxin-free buffer TE.