Determination of Iron in Natural and Drinking Waters by Stripping Voltammetry

Abstract

Polyvalent metals incorporated in enzymes, hormones, and vitamins play an important role in biochemical processes. Because of their ability to change the oxidation state, they serve as electron carriers and participate in the regulation of such important processes as, for example, respiration and photosynthesis. Iron belongs to these metals first of all. Deficiency of iron in a human body retards its growth, makes breathing difficult, causes anemia, and reduces the levels of the production of immune cells. Iron is considered a key metal in energy transformations that occur in green plants and are required for synthesis and other vital processes in cells. Natural water is one of the sources of iron ingress to living organisms from the biosphere.The maximum permissible concentration for iron(III) is 0.3 mg/L in fresh water and 0.05 mg/L in sea water [1]. In actual practice, the concentrations of soluble iron species in natural waters vary from 10 -6 M for river water to 10 -9 M for coastal sea water and to 10 -11 M for ocean water, respectively [2]. Atomic-absorption spectrometry, inductively coupled plasma-mass spectrometry, and stripping voltammetry (SVA) are used for determining trace amounts of iron(III) in natural water. SVA differs from the other methods by its simplicity, compactness, and inexpensive equipment and can be used at the place of sampling. Stationary mercury-drop [2-13] and a mercury-film [14, 15] electrodes are usually used for determining iron(III) by SVA. To lower the detection limit for iron(III) at a mercury electrode to 10 -9 -10 -10 M, organic reagents are used. 1-Nitrozo-2-naphthol [2, 3, 11], catechol [4, 14], 2,3-dihydroxynaphthalene [5, 6], Solochrome Violet [9, 15, 16], Cupferron [10], and 2-(5'-bromo-2'-pyridylazo)-5-diethylaminophenol [12,13] are used most often. However, the extremely high toxicity of metallic mercury makes researchers search for ecologically safe electrodes. A thick-film graphite-containing electrode modified with calomel (TFGME) [17] belongs to such electrodes. In the course of analysis, a very thin dropletlike mercury coating is formed, but, in spite of this, this electrode can be considered safe, because, after analysis, the thin mercury layer can be easily and completely converted back to calomel.This work is dedicated to the development of a procedure for determining trace amounts of iron(III) ions in natural and drinking waters by SVA using a nontoxic thick-film modified graphite electrode. EXPERIMENTALThe reagents used were of high-purity or cp grades. All solutions were prepared with triply distilled water. Solutions of iron(III) of different concentrations (from 10 -2 to 10 -3 M) were prepared by diluting a solution of a certified reference material of Fe(III) (GSO 7254-96) containing 1 mg/mL iron(III) ions with triply distilled water. The supporting electrolytes were 0.01 M ammonia, 0.1 M acetate, and 0.07 M phosphate buffer solutions, a 0.1 M universal buffer mixture, a 0.1 M sodium acetate solution, and a 0.01 M TRIS (hydroxymethylaminomethane) buffer ...

Electrochemical technique to measure Fe(II) and Fe(III) concentrations simultaneously

“…In addition, different oxidation states of iron ions play different roles. Therefore, simultaneous and accurate quantitative determination of the concentrations of Fe(II) and Fe(III) ions separately is of major significance not only in environmental chemistry [2][3][4] and biochemical engineering [5][6][7], but also in many scientific [8,9] and industrial fields [10,11]. Traditional techniques, such as atomic absorption spectroscopy (AAS), ion chromatography (IC), and colorimetric method have been generally known as analytical techniques for determining the concentrations of cations; however, these techniques can not distinguish the differences in metal valences.…”

Thick-film carbon-containing electrodes modified with multi-walled carbon nanotubes in adsorptive stripping voltammetry of iron(III)

“…The measurements were performed with an IVA-5 stripping voltammetric analyzer (produced by OOO NPVP IVA, Yekaterinburg, Russia) equipped with a magnetic stirrer and with IVA 2003 software, with the determination of Fe(III) ions in a model solution by the known AdSV procedure as example [24]. A glassy carbon rod 0.4 cm in diameter was an auxiliary electrode, and an ESr-10107 silver chloride electrode (Ag/AgCl/3 M KCl, ООО Izmeritel'naya Tekhnika, Moscow) was a reference electrode.…”

Preconcentration Versions and New Sensors in Stripping Voltammetry

“…In determining Cu 2+ , Pb 2+ , Cd 2+ , and Zn 2+ , 1-(o-chlorophenyl)-3-phenyl-5-(6-methyl-4-hydroxy-pyrimidinyl-2)formazan [19,20] was used as a modifier of TGEs. TGEs modified with 2,3-diaminonaphthalene [21], nitroso R salt [22], pyrocatechol [23], 1,10-phenanthroline [24], and 1-(o-tolyl)-3-methyl-5-(1-benzylbenzimidazolyl-2)formazan [25] were used for determining Se 4+ , Co 2+ , Fe 3+ , Fe 2+ , and Mn 2+ , respectively. The A-Ch-E sequence of electrode reactions was the most typical of the preliminarily modified TGEs, and the Ch-A-E sequence, of the in situ modified electrodes.…”