Quantitative in-situ and localized analytical methods that can monitor Mg2+ release are central to probe the impact of the microstructure on magnesium alloy corrosion. As such, a potentiometric micro-Mg2+ ion-selective membrane electrode is fabricated, calibrated, characterized and used to selectively monitor the Mg2+ release from different cast Mg AM50 alloys during corrosion. We demonstrate that the local Mg2+ release is tied to the alloy microstructure and its aluminum distribution, indicating a possibility of optimization of the base material corrosion properties. (C) 2014 Elsevier B.V. All rights reserved.