A pulse tracer test was performed with an

initial concentration of $9$ mg$/$L$,$ and the following data were collected:

time $($min$)$: $31\mathrm{.}3,35\mathrm{.}8,40\mathrm{.}3,44\mathrm{.}7,49\mathrm{.}2,$

$53\mathrm{.}7,58\mathrm{.}2,62\mathrm{.}6,67\mathrm{.}1,71\mathrm{.}6,76\mathrm{.}1,80\mathrm{.}5$

conc. $($mg$/$L$)$: $9,9\mathrm{.}78,24\mathrm{.}6,104,251,$

$291,181,71\mathrm{.}4,22\mathrm{.}8,11,9\mathrm{.}2,9\mathrm{.}02$

What is the normalization concentration, CN $,$

of the tracer test?