Microelectrode Procedures for the Analysis of Silicate and Phosphate — Towards Practical Procedures

Abstract

Amperometric methods using microdisk electrodes and based on the formation of electroactive molybdophosphate and molybdosilicate complexes are described for the determination in water samples of phosphate and silicate. It is demonstrated that it is possible to devise conditions for the analysis of 1-100 mM phosphate or silicate in the presence of a large excess of the other. It is also possible to determine both phosphate and silicate in a single analysis provided they are present in not too dissimilar concentrations.

Investigation of amperometric detection of phosphate

“…However, if the mixed silicate/molybdate solution was left more than 5 min, the response of silicate appeared indicating the slow formation of molybdosilicate complexes. This observation was in agreement with the work of Hodgan and Pletcher [28]. The interference of silicate was successfully avoided by adding oxalate at 0.25% as masking agent to the mixed molybdate/nitric acid solutions in agreement with the work of Galhardo and Masini [29].…”

Silicon-based electrochemical microdevices for silicate detection in seawater

“…In the first compartment, 3 mL of sample is placed together with a molybdenum electrode and the reference electrode (Ag/AgCl/KCl 3 mol L −1 ). A platinum counter electrode is placed in the second compartment, on the other side of the non-proton exchange membrane, to limit the diffusion of H + produced, avoid their reduction and obtain the required acidic pH for the complexation of silicates with molybdates [49,50]. Then the silicomolybdic complex is detected by cyclic voltammetry (CV) using a gold or platinum working electrode immersed in the compartment of the cell ( two oxidation peaks at 0.31 V and 0.41 V. In this work, the analytical signals have been either the intensity current in the reduction peak at 0.38 V (the most precise) or the oxidation intensity current at 0.41 V. Finally, a cleaning procedure for the working electrode must be applied.…”

“…Different concentrations of silicate were prepared between 0. 50 and from 8.42 to 134.8 mol L −1 in sodium chloride solution, to cover the whole range of those found in the open ocean. An external Ag/AgCl/KCl (3 mol L −1 ) reference electrode was used for all the measurements.…”