In ac polarography, differential pulse polarography, derivative polarography, square-wave polarography, and similar techniques, the maximum value of the component of the current that is associated with the presence of a substance B. Normally this component of the current is faradaic, and the maximum arises because the rate of variation (with applied potential) of the rate of the charge-transfer process passes through a maximum. Similar maxima arise when this component is non-faradaic (and when B is surface-active rather than electroactive). In a case known to be of the latter type, the term apex current is recommended as being more specific.
PAC, 1985, 57, 1491. 'Recommended terms, symbols, and definitions for electroanalytical chemistry (Recommendations 1985)' on page 1499 (https://doi.org/10.1351/pac198557101491)