We use standard addition methods when our sample has matrix effects which are hard to duplicate in a blank. Let's again find the amount of Pb+2 in a blood sample. A 5.00 mL blood sample containing lead yielded a signal of 0.712 units. Afterwards, the sample was spiked with 5.00 ?L of 1560 ppb Pb+2 standard. (note: a small addition) This spiked solution gave a reading of 1.546 units. Find the concentration of Pb+2.
[X]i / [X]f + [S]f = Ix / Is+x