Step 1 — deposition. The working electrode is held at a fixed negative potential Edep while metal ions in solution are reduced and electroplated onto its surface, pre-concentrating trace metal from a dilute sample into a small, analyzable deposit:
M(n+) + n e− → M(0) on electrode
N_dep = k · C · t_dep · η(E_dep)
η(E_dep) = 1 / (1 + exp(−(E0_M − E_dep)/40mV)) (deposition efficiency)
η is a logistic switch: each metal only plates efficiently once Edep is more negative than its own reduction potential E0. Cu (least reducing) deposits at almost any negative potential; Cd (most reducing) needs the most negative Edep — set it too positive and the Cd row under-reports.
Step 2 — anodic stripping. The potential is then swept positive at a fixed scan rate v. Each deposited metal re-oxidizes and leaves the electrode exactly at its own characteristic potential Ep, producing a current peak. For a thin deposited film this is a reversible surface-confined process with an exact closed-form peak shape:
i(E) = ip · sech²[ (E − Ep) / w ], w = 3.53RT/(2.634 nF)
ip ∝ n · v · N_dep (peak height ∝ scan rate × amount deposited)
FWHM = 90.6/n mV at 298 K (peak width, n = 2 for Cd²⁺/Pb²⁺/Cu²⁺)
The fraction of a metal's deposit already stripped by potential E is 0.5(1+tanh((E−Ep)/w)), whose derivative is sech²((E−Ep)/w)/(2w) — proportional to, but exactly half the naive sech²/w some write; that factor of 2 (dropped in the original 3D build's comment, verified numerically here) is what keeps the "atoms leaving the electrode" animation and the current trace in the same phase without over-stripping early.
- Sample concentration — scales the true Cd/Pb/Cu content of the "unknown" being analyzed.
- Deposition potential / time — control how completely and how much metal is pre-concentrated.
- Scan rate — faster sweeps give taller, narrower peaks (ip ∝ v) exactly as in a real potentiostat.
- The estimated concentration column inverts the calibration and will under-report a metal whose deposition efficiency η was below 100% — a real, common ASV pitfall.
Real-world relevance: anodic stripping voltammetry with disposable screen-printed or bismuth-film electrodes is the standard field method for detecting Pb, Cd and Cu at parts-per-billion levels in drinking water and soil extracts.
Drag the cell view to pan, and scroll/pinch to zoom in on the electrode surface while atoms plate and strip.