A group of researchers have described a stripping analysis method for determining tin in canned fruit juices. In one case, standards of 50.0 ppb Sn4+, 100.0 ppb Sn4+, and 150.0 ppb Sn4+ were analyzed giving peak currents (arbitrary units) of 83.0, 171.6, and 260.2, respectively. A 2.00-mL sample of lychee juice is mixed with 20.00 mL of 1:1 HCl/HNO3. A 0.500-mL portion of this mixture is added to 10 mL of 6 M HCl and the volume adjusted to 30.00 mL. Analysis of this diluted sample gave a signal of 128.2 (arbitrary units). Report the parts-per-million Sn4+ in the original sample of lychee juice.

The parts-per-million Sn⁴⁺ in the original sample of lychee juice is 7.551 × 10⁻² ppm.

Explanation:

Here we note that

Concentration                                                 Peak Currents

50.0 ppb                                                           83.0

100.0 ppb                                                         171.6

150.0 ppb                                                         260.2

Plotting the above values we have the linear equation

Slope, m = = 1.772

The x intercept = is gotten by placing y = 260.2 and solving for c as follows

Therefore 260.2 = 1.772·150.0 + c

c = 260.2 - 1.772·150.0 = -5.6

Therefore the linear equation is of the form

y = 1.772× x -5.6

Therefore when the signal = 128.2 we have,

128.2 = 1.772× x -5.6

∴ x = ppb = (128.2 +5.6)/1.772 = 75.51 ppb = 7.551 × 10⁻² ppm.