Accuracy/Recovery

Following the procedure，either 10 or 50 ng of purified pIL-2 plasmid DNA was spiked per 10 μl into cell suspensions of lots A and B either prior to DNA isolation（front spike），or after DNA isolation，prior to agarose gel electrophoresis（back spike）.The unspiked bacterial DNA sample as well as 50 or 10 ng of pIL-2 plasmid DNA was run in the agarose gel along with the spiked sample DNA.The negative of the gel was scanned.The spike recovery for each sample dilution was calculated using the formula：

%spike recovery

The results are summarized in Table 4.Values for each sample were obtained from the means of spike recovery values at dilutions 1，2，4，and 8（see Materials and Methods）.Percentage recovery values for sample lot A before and after DNA isolation were 88%±1%and 98%±4%，respectively.Percentage recovery values for sample lot B before and after DNA isolation were 90.5%±7.5%and 86.5%±6.5%，respectively.

Table 4　Accuracy/Spike recovery in plasmid copy number assay