Voltammetrische technieken: pulsvoltammetrie

Differential-pulse voltammetry (DPV) applies small potential pulses superimposed on a linear potential ramp, measuring current before and after each pulse. The current difference is plotted against applied potential, eliminating interfering charging current that obscures signals in voltammetric techniques linear-scan methods. This approach provides excellent resolution and enables accurate analyte concentration determination.

In differential-pulse voltammetry, the magnitude of the differential current—the difference between current measurements before and after each potential pulse—is directly proportional to the concentration of the electroactive species in solution. This linear relationship allows quantitative determination of analyte concentration from the voltammogram peak height.

Square-wave voltammetry combines a square wave and staircase potential, reducing the analyte during cathodic pulses and reoxidizing it during anodic pulses. The polarogram plots the current difference between anodic and cathodic peaks. Since these opposing currents have different signs, their difference produces a larger net current directly proportional to analyte concentration.

Square-wave voltammetry generates larger signals because it measures the difference between anodic and cathodic currents with opposing signs. This difference amplifies the net faradaic current compared to linear methods, which measure only one current direction. The enhanced signal improves sensitivity and reduces interference from capacitive background currents.

Differential-pulse voltammetry demonstrates relative inertness to capacitive currents, which typically interfere with signal detection in other voltammetry techniques. By measuring the differential current between two points and applying potential pulses at specific intervals, DPV effectively suppresses the charging current contribution, allowing faradaic current from redox reactions to dominate the measurement.

When a potential pulse is applied to an electrochemical cell in differential-pulse voltammetry, it drives redox reactions at the electrode surface. Electrons transfer between the electrode and analyte species in solution, generating faradaic current. Measuring current before and after each pulse isolates this faradaic component from background charging current.

Differential-pulse voltammetry offers excellent resolution, allowing separation of voltammetric signals from multiple species present simultaneously in solution. The technique's ability to suppress capacitive currents and measure differential faradaic current at each potential step produces sharp, well-defined peaks for each electroactive species, enabling accurate identification and quantification.