A dNTP master-mix is prepared by combining $40 \mu L$ of each $20 \mathrm{mM}$ dNTP stock (dATP, dCTP, dGTP and dTTP). $4 \mu L$ of this dNTP master-mix is added to a PCR mix and the final volume is adjusted to $50 \mu L$. The concentration (in $\mu M$ ) of total dNTPs in the $\text{PCR}$ mix is _____________.