Beryllium ion sensing through the ion pair formation between the electrochemically reduced ferrocenyl naphthoquinone radicals and Be ^{2 +} ions

Abstract: We explored the mechanistic aspects of ion pair formation between electrochemically reduced radicals (Fc–cnq–1a∙-/Fc–cnq–1b∙-) and dianions (Fc–cnq–1a^{2 -}/Fc–cnq–1b^{2 -}) of ferrocenyl naphthoquinones (Fc–cnq–1a and Fc–cnq–1b) and several metal ions by cyclic voltammetry (CV), square wave voltammetry (SWV) and spectroelectrochemistry, for the first time. The experiments demonstrated that Fc–cnq–1a^{2 -}/Fc–cnq–1b^{2 -} were moderately affected with Na⁺, K⁺ and Cs⁺ by slightly shifting to the anodic side, but were strongly influenced with Li⁺ ion. Fc–cnq–1a∙-/Fc–cnq–1b∙- were not affected by alkali metal ions, indicating no ion pair formation between the radicals and these ions. Fc–cnq–1a^{2 -}/Fc–cnq–1b^{2 -} was not evolved in the presence of Be^{2 +}, Mg^{2 +} and Ca^{2 +}, but Fc–cnq–1a∙-/Fc–cnq–1b∙- appeared with their cathodic waves, and participated with intermediates, [(Fc–cnq–1b)2∙-–Be^{2 +} and [(Fc–cnq–1a)∙-–Cl]. The most pronounced effect on the ion-pair formation of the Fc–cnq–1a∙-/Fc–cnq–1b∙- was observed in Be^{2 +}, indicating that Fc–cnq–1a or Fc–cnq–1b can selectively sense ultra-trace amount of Be^{2 +} (LOD = 3.6 ppb) among the other metal ions with SWV titration, for the first time, based on the strong ion pair formation reaction between the radicals and Be^{2 +}. Graphical abstract: Synopsis Ultra-trace amount of beryllium ion (Be ^{2 +}) sensing (LOD = 3.6 ppb) through the ion pair formation between the electrochemically reduced ferrocenyl naphthoquinone radicals (Fc–cnq–1a∙-/Fc–cnq–1b∙-) and Be ^{2 +} ions by cyclic voltammetry (CV), square wave voltammetry (SWV), and for the first time spectroelectrochemistry is reported in this study. [Figure not available: see fulltext.].