[StS]

Linear scan polarography was used to quantitate cadmium in river water by the single-point standard addition method.  For each of the four solutions (a-d), calculate the Cd 2+ concentration in the original (undiluted) samples.

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         Volumes used, mL                                   Solution
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Sample   KCl      Cd 2+      H2O      Current
         0.400 M   2.00 mM              μA
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15.0      20.0      0.00      15.0      79.7               a
15.0      20.0      5.00      10.0      95.9

10.0      20.0      0.00      20.0      49.9               b
10.0      20.0      10.0      10.0      82.3

20.0      20.0      0.00      10.0      41.4               c
20.0      20.0      5.00      5.00      57.6

15.0      20.0      0.00      15.0      67.9               d
15.0      20.0      10.0      5.00      100.3

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I am just wondering if the concentration of KCl is needed. Since the amount stays constant I just have to include its volume with the sample volume and H2O volume to make up the total volume before addition of standard, right?

[Pradeep]

Is this single point standard addition?

You have 4 calibration points including zero addition. This a multi point addition.

Why dont you make a plot?

The intercept on X axis will give the conc. of Cd2+ in your sample. Then calculate with dilution factor.