Flow injection potentiometric determination of Fe(III) using a fluoride-selective electrode as detector

Abstract

Flow injection analysis (FIA) with different sensors is rapidly developing into a powerful analytical tool with many merits, such a broad scope and rapid sample throughput.Over many years, there has been a great deal of research and development in flow injection systems using ion-selective electrodes (ISEs) as detectors [1]. Many systems were evaluated using ISEs in flow injection potentiometry (FIP), and continuous flow modes [2,3].The fluoride ion-selective electrode (FISE) with LaF 3 membrane is probably the most widely applied ion-selective electrode used for practical measurements. Since the FISE was developed (1966), the formation constants of many metal fluoro complexes in aqueous solution have been determined. However, there are very few reports in which the FIA determination of metal ions, or their influence on the response characteristics of the fluoride ion-selective electrode, based on metal fluoride complex formation are discussed [4][5][6][7].Suitability of the FISE for monitoring a reasonably fast reaction of the formation of FeF 2+ in acidic solution has been previously established [8]. Oehme and Dolezalova [9] reported the possibility of direct potentiometric determination of Fe 3+ based on iron-fluoride complex formation but no detailed information was given.Previous investigation [10] has shown that FISE can be applied successfully for kinetic potentiometric determination of Fe(III) in batch experiment. The kinetics of the FeF 2+ formation reaction were studied in acidic solution (pH = 1.8; 2.5). The initial rates of iron-fluoride complex formation in the solution, calculated from the non-steady-state potential values recorded after addition of Fe(III), were shown to be proportional to the analytical concentration of this ion in cell solution.In this work we developed a simple FIA system with an commercial FISE as detector. This system was applied for the determination of iron in the range of concentration from 10 -4 mol L -1 to 10 -1 mol L -1 . Experimental ReagentsAll chemicals were of analytical-reagent grade and were used without further purification. All solutions were prepared with water doubly distilled in glass.Standard sodium fluoride solution, 0.1 mol L -1 , was prepared in a polypropylene calibrated flask from dried (0.1 MPa, 110°C) sodium fluoride. Dilute standard fluoride solution was prepared from the stock solution, using polypropylene flask and a pipette.A stock iron(III) solution of approximately 0.1 mol L -1 was prepared by weighing and dissolving an appropriate amount of iron(III) nitrate in 1 mol L -1 perchloric acid. Other solutions of iron were prepared from the stock solution by dilution with 0.01 mol L -1 perchloric acid. Concentration of the ferric ion in the solution was estimated by titration with a standard solution of EDTA, using sulfasalicylic acid as indicator.

Kinetic Methods of Analysis with Potentiometric and Spectrophotometric Detectors – Our Laboratory Experiences

“…FIA system with cascade flow cell equipped with commercial FISE as detector has been described [34]. This system was applied for the determination of iron in the range of concentration from 1.010 -4 to 1.010 -1 mol L -1 .…”

Development of the New Fluoride Ion-Selective Electrode Modified with FexOy Nanoparticles

“…After the removal of Fe x O y NPs from the membrane surface, the response properties were improved for all electrodes tested. It is possible that iron from the oxide reacted with the F − ions (reaction 2) from the solution to form an FeF 2 + or FeF 2+ complex [19], which influenced the electrode reaction or contributed to the improved conductivity, since Fe was embedded in the membrane itself, as shown by the elemental analysis of the membrane (Table 4) and the changes observed on the membrane of the electrode surface.…”

Electroanalytical Flow Measurements

“…12 Indirect determination of Fe(III) in FIA system with fluoride ISE was based on formation of FeF 2+ complex in acid solution. 13 FIA systems were also developed for numerous biocatalytic determinations with potentiometric detection. An urea biosensor with urease covalently bound to the carboxylated PVC based ammonium ISE was used in FIA system for the determination of urea in human serum samples 14 and for hemodialysis 15 control.…”