Three pretreatment technologies for the highly sensitive electrochemical quantification of mercury in soil in the presence of interfering substances

To comply with current regulations on permitted levels of mercury (Hg) in soil, highly accurate and sensitive techniques are required to quantify soil Hg levels. With suitable solvent pretreatment, the electrochemical detection of Hg in the resulting soil eluates can be performed simply and with a sensitivity similar to that of expensive (e.g., mass spectrometric) methods at a fraction of their cost. However, unlike mass spectrometric analysis, which relies on columns to prepare homogeneous samples, electrochemical Hg detection suffers from the difficulty of ensuring stable measurement conditions. The preprocessing complexity of the latter method makes it unsuitable for on-site detection, and its application as an alternative to high-precision instrumental analyses remains limited. We address this problem in this study via a method for highly sensitive electrochemical Hg detection in soils, based on simple soil pretreatment involving filtration to remove large particles, cyclic interfacial electrolytic cleaning, concentration during chemical pretreatment, solution exchange after pretreatment, and electrochemical measurements. The detection limit of the developed method (0.25 ppb) meets the regulatory limit for Hg in soil.