Effects of chloride ion concentration on mercury(I) chloride formation during ex situ and in situ mercury deposition with selected electrode substrates and electrolytes

Ex situ and in situ mercury film formation was investigated in solutions co ntaining NO3-, SCN-, Cl-, and ClO4- and at glassy carbon macro- (3 mm) and micro- (10 mu m) electrodes, a platinum macro- (1.6 mm) electrode, and a mi crofabricated Ir-ultramicroelectrode away (Ir-UMEA), The formation of mercu ry(I) chloride (calomel) during Hg deposition was investigated by varying t he Cl- concentration. The performance of the Hg films was evaluated using C d2+ and Pb2+ with square wave anodic stripping voltammetry. For ex situ Hg film formation on Ir and GC substrates, the highest efficiency was obtained when no Cl- or 1 M Cl- was present. The Pt surface was affected by the Cl- ions; thus for ex situ Hg film formation, the best results were obtained w ith no Cl- present. Calomel formation during in situ Hg deposition occurred for 0.001 [Cl-] < 0.5 M and was independent of the substrate. Calomel inte rference was identified by the presence of an anomalous cathodic peak betwe en -0.6 and -0.3 V during the anodic scan. For in situ Hg film formation, t he Pb2+ stripping peak current increased with increasing ionic strength, wh ile the Cd2+ peak current increased dramatically in the presence of SCN- or Cl-. Although conditioning of the Ir-UMEA and Pt macroelectrode eliminated the cathodic peak, calomel still remained on the surface after the Hg film was removed. When the cathodic peak was present, no calomel remained after removal of the Hg film; thus for in situ film formation, the calomel inter ference can be avoided. When [Cl-] > 0.01 M, the best results can be obtain ed by adjusting [Cl-] to 1 M, For [Cl-] < 0.01 M, addition of SCN- is recom mended. Although analyses can be preformed without any Cl- present, precaut ions should be taken to avoid unintentional contamination.