Preparation of a 2-(4-fluorophenyl)indole-modified xerogel and its use for the fabrication of screen-printed electrodes for the electrocatalytic determination of sulfide Original Research Article

The preparation of a 2-(4-fluorophenyl)indole-modified xerogel (FPIX), pure or further modified with platinum (Pt-FPIX) and their use for the fabrication of screen-printed electrodes for the electrocatalytic determination of sulfide in synthetic and real samples is described. Synthesis protocol and some preliminary identification studies of 2-(4-fluorophenyl)indole-modified xerogel are given. The fabrication of FPIX screen-printed electrodes (SPEs) and the preparation of FPIX and Pt-FPIX chemically modified graphite electrodes (CMEs) by using a mixture of FPIX/graphite-based polymer thick film ink are also described. The electrocatalytic behavior of the FPIX- or Pt-FPIX-CMEs to sulfide was tested with cyclic voltammetry (CV). The optimization of various working parameters such as xerogel loading, working pH, utilization of a cellulose acetate outer protective membrane, as well as the interference effect of various reducing compounds was also tested with CV or amperometric measurements in both, batch and flow conditions. Discrimination between the electrocatalytic effect of FPIX on the sulfide oxidation and the increase of the film conductivity being induced from the incorporation of platinum in the xerogel, regarding their contribution to the overall measuring signal was attempted by impedance spectroscopy. FPIX-SPEs, poised at +450 mV versus Ag/AgCl, at pH 5.5 were utilized for the determination of sulfide in synthetic and real samples. The proposed method correlates well with a colorimetric method. Calibration graphs were linear over the range 0.01–2.0 mM sodium sulfide and the RSD was 2.2% (0.25 mM sodium sulfide, n = 12). Recovery ranged from 93 to 105%. FPIX-SPEs showed both very good working and storage stability. They retain almost 95% of their initial activity after 50–60 runs and can be stored at room temperature with no remarkable loss of their activity for more than 1 month.