b) The two electrodes most commonly used in ASV are the hanging mercury drop electrode
(HMDE) and the mercury film electrode (MFE). Which of them offers better sensitivity? Why?
Which of them offers better dynamic range? Why?
c) Cr(VI) in soil from a hazardous waste site was analyzed by digesting 5.0 g of the soil in 15.0
mL of ultrapure $HNO_3$ using microwave digestion. For anodic stripping voltammetry, a 50 µL
aliquot of the digest was injected into the supporting electrolyte and the volume was brought to
20.0 mL. In the figure, curve a is the electrolyte blank; curve b is the unknown solution, and
curves c-e show successive additions of Cr(VI) standard, each one increasing Cr(VI) mass in
the solution by 0.50 µg. Find the concentration of Cr(VI) in the soil in ppm (mg/kg soil).
Notes: 1) For best results, print the figure from the next page to measure peak heights. 2) The
figure shows voltammograms shifted vertically with respect to each other for easier
visualization. Consequently, you have to draw a separate baseline for each individual
voltammogram and measure the height from the baseline of a given peak to its apex, as
illustrated for curve b. 3) The signal for the blank must be subtracted from the signals of all the
samples.
