The preconcentration at modified electrode is analogous to trace analysis by the electrochemical technique called stripping voltammetry. The target analyte is accumulated from a dilute solution into the modified electrode layer and subsequently reduced or oxidized by a linear potential sweep (cyclic voltammetry, CV) or by a pulse potential modulation (differential pulse voltammetry, DPV; or square wave voltammetry, SWV) (Scheme 2).