Chemistry Labs

Analytical chemistry

Potentiometry, voltammetry, polarography

Potentiometry measures equilibrium potential; voltammetry measures current during a controlled potential program.

1 Lower secondary2 Upper secondary3 Undergraduate4 Advanced5 Research

IntuitionIntuition: the measurement idea

Electrochemistry can measure either an equilibrium potential or a current that develops while an electrode potential changes. One probes thermodynamics, the other probes transport and kinetics.

Explore the Potentiometry, voltammetry, polarography measurement concept in this interactive signal.

SchoolSchool level: signal and result

Potentiometry measures a potential related to activity; voltammetry scans potential and records current; polarography is voltammetry at a dropping-mercury electrode.

Definition:

Potentiometry measures equilibrium potential; voltammetry measures current during a controlled potential program.

First identify the measurand, choose a signal that responds to it, and compare the sample with a calibrated standard or a validated model.

E=E∘−RTnFln⁡Q,ip=2.69×105n3/2AD1/2Cv1/2E=E^\circ-\dfrac{RT}{nF}\ln Q,\qquad i_p=2.69\times10^5 n^{3/2}AD^{1/2}Cv^{1/2}

Example: Worked analytical example

Calculate the analyte result from the stated measurement and method relation.

Solution

At 25 °C, a one-electron reversible couple in cyclic voltammetry has ideal peak separation ΔEp ≈ 59 mV; larger separation can indicate uncompensated resistance or quasi-reversible kinetics.

Method checkpoints
StagePurpose
PrepareControl matrix and contamination
MeasureAcquire a calibrated response
ValidateCheck recovery and uncertainty

UndergraduateUniversity: quantitative method

A potentiometric measurement uses a nearly zero-current indicator electrode and Nernstian response. Voltammetry records current under a programmed potential; the shape reflects diffusion, adsorption, kinetics and coupled chemistry.

Calibration, selectivity, sample preparation and uncertainty belong to the method itself, not to afterthoughts. Report units, conditions and the calibration range.

E=E∘−RTnFln⁡Q,ip=2.69×105n3/2AD1/2Cv1/2E=E^\circ-\dfrac{RT}{nF}\ln Q,\qquad i_p=2.69\times10^5 n^{3/2}AD^{1/2}Cv^{1/2}

References