The eu(iii) standards added to the groundwater sample contained 0.168 ng/ml (ppb) of eu(iii). calculate the concentration of eu(iii) in the groundwater sample.

The standard addition equation is as followsI_(S+X) (V/V_O )=I_X+I_X/[X]_i  [S]_4 (V_S/V_0 ) Here, [X]_i is the initial concentration of analyte, [S]_i is the initial concentration of standard, I_X is signal for analyte, I_(S+X) is signal for standard and analyte, V_0 is the initial volume, V_S is the added standard volume, and V is the total volume.Added volume of standard V_S is-23.3 mL. Initial volume of the sample V_0  is 10.00 mL. Initial concentration of standard ([S]_i) is 0.156 ng/mL.[X]_i= -[S]_i (V_S/V_0 )〖[X]〗_(i )= -(0.156 ng/mL)((-23.3 mL)/(10.00 mL))=0.363 ng/mL
Concentration of U(III) in ground sample is 0.363 ng/mL

Answer; carbon monoxide (co);