Screen-printed electrodes covered by mercury film or meniscus

For the first time, silver screen-printed electrodes covered by mercury film (MF-AgSPE) and mercury meniscus (m-AgSPE) were designed, prepared and tested. The precise electrochemical preparation procedure for mercury deposition at the silver working electrode (WE) surface of commercial AgSPE was used. A simple and quick way to prepare m-AgSPE is transferring a precisely defined mercury drop from a hanging mercury drop electrode (HMDE) at WE. Deposited mercury dissolves silver and it gradually converts into solid or paste amalgam. The potential of hydrogen evolution with these electrodes has maximum values in aqueous solutions and is comparable to that on mercury electrodes. The 20 µm thick mercury film allows working with the liquid surface during the day and its deposition takes approximately 15 min. Testing of MF- and m-AgSPEs was performed by voltammetric methods with and without accumulation of analytes on the electrode, in a batch electrode arrangement and also in a flow-through system. For comparison, measurements were carried out with printed solid amalgam electrodes, HMDE, and also with the original commercial AgSPE. Simultaneous measurement of zinc, cadmium, lead, and copper cations on m-AgSPE by stripping voltammetry allowed to determine their concentrations <1 µg L^-1. Comparison of measurements with the printed pseudo-reference electrode of SPE and an external calomel electrode showed that the differences in the peak potentials can be up to 200 mV. Commercial large-scale production of printed electrodes makes them a practically unlimited source for the rapid preparation of inexpensive electrodes with an ideally smooth liquid surface.