A spectrophotometric method for the quantitative analysis of Pb$2+$ in blood yields an S

samp of $0\mathrm{.}193$ when a $1\mathrm{.}00$ mL sample of blood is diluted to $5\mathrm{.}00$ mL$.$ A second $1\mathrm{.}00$ mL

sample of blood is spiked with $1\mathrm{.}00$L of a $1560-$ppb Pb$2+$ external standard and diluted

to $5\mathrm{.}00$ mL$,$ yielding