Response mechanism of a neutral carrier Hg(II) polymeric membrane ion-selective electrode. SEM and EDAX study

Abstract

Scanning electron microscopy (SEM) and energy dispersive atomic X-ray spectrometry (EDAX) were used to study the response mechanism of a previously reported new Hg membrane ion-selective electrode (ISE) based on 1,3-diphenylthiourea. These techniques allowed the study of the membrane surface characteristics, such as the morphological homogeneity and chemical composition. A ‘twice Nernstian’ response at pH ≥ 7 was explained by the detection of the Hg(OH)⁺ cation. A normal Nernstian response was found at acidic pH values. Using these techniques, both coordination compounds, [Ligand–Hg–OH] at pH 7 and [Ligand–Hg–Ligand] at pH 4.5, were confirmed on the electrode membrane surface activated with Hg(NO₃)₂ solution at both pH values. These methods provide results which are independent of the potential measurement data and in agreement with them. A successful response model has explained both independent and unbiased sets of results. These conclusions confirm the proposed response mechanisms for this new Hg membrane sensor.