Standard addition graph. The figure shows standard additions of Cu^2+ to acidifi

Question

Standard addition graph. The figure shows standard additions of Cu^2+ to acidified tap water measured by an electrochemical method. The standard additions had negligible volume compared with that of the tap water sample, so you can consider all solutions to have the same volume. The signal is the peak height (in mu A), which you will need to measure relative to the baseline in the figure. Find the concentration of Cu^2+ in the tap water. Five standard additions of 100 ppb Cu^2+ to tap water. [From M. A. Nolan and S. P. Kounaves, Anal. Chem. 1999, 71, 3567.]

Explanation / Answer

From the above shown graph,

The current value for sample without any standard = 1.0 uA

the current value for sample + 100 ppb standard = 1.2 uA

let x be the concentration of Cu2+ in the tap water,

then,

x/(x + 100) = 1/1.2

1.2x = x + 100

x = 100/0.2 = 500 ppb

So the concentration of Cu2+ in tap water = 500 ppb

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