Iodate Concentration Research Articles

Nano-scale islands of ruthenium oxide as an electrochemical sensor for iodate and periodate determination

In this study, a promising electrochemical sensor was fabricated by the electrodeposition of nano-scale islands of ruthenium oxide (ruthenium oxide nanoparticles, RuON) on a glassy carbon electrode (RuON–GCE). Then, the electrocatalytic oxidation of iodate and periodate was investigated on it, using cyclic voltammetry, chronoamperometry and amperometry as diagnostic techniques. The charge transfer coefficient, α, and the charge transfer rate constant, ks, for electron transfer between RuON and GCE were calculated as 0.5 ± 0.03 and 9.0 ± 0.7 s−1 respectively. A comparison of the data obtained from the electrocatalytic reduction of iodate and periodate at a bare GCE (BGCE) and RuON–GCE clearly shows that the unique electronic properties of nanoparticles definitely improve the characteristics of iodate and periodate electrocatalytic reduction. The kinetic parameters such as the electron transfer coefficient, α, and the heterogeneous electron transfer rate constant, k′, for the reduction of iodate and periodate at RuON–GCE surface were determined using cyclic voltammetry. Amperometry revealed a good linear relationship between the peak current and the concentration of iodate and periodate. The detection limits of 0.9 and 0.2 μM were calculated for iodate and periodate respectively.

Properties of Alumina Coagulated Bodies Prepared by Direct Coagulation Casting via High Valence Counter Ions (DCC‐HVCI)

Alumina green bodies were prepared by direct coagulation casting via increasing high valence counter ions (DCC‐HVCI) method. Influence of calcium iodate concentration, coagulation temperature, and the solid loading on the compressive strength of coagulated bodies was investigated. The results show that the wet‐coagulated bodies display higher compressive strength than dried ones. The wet strength is above 2.0 MPa which is about one order higher than that prepared by DCC method, whereas the dried strength is in the range of 1.0 MPa. The wet‐coagulated body shows elastic deformation, whereas the dried body exhibits typical brittle failure behavior. The mechanism of high wet strength obtained by DCC‐HVCI is also proposed. The coagulated bodies prepared from slurries of alumina loading in the range of 50 vol% showed linear shrinkage of 2.6% after drying at 80°C for 24 h. The sample with the powder content of 50 vol% displays a narrow average pore channel size, showing a mean pore diameter of 40 nm. A homogeneous green body and high wet strength can be obtained via the DCC‐HVCI method.

Modification of glassy carbon electrode with a polymer/mediator composite and its application for the electrochemical detection of iodate

A modified glassy carbon electrode was prepared by depositing a composite of polymer and mediator on a glassy carbon electrode (GCE). The mediator, flavin adenine dinucleotide (FAD) and the polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) were electrochemically deposited as a composite on the GCE by applying cyclic voltammetry (CV). This modified electrode is hereafter designated as GCE/PEDOT/FAD. FAD was found to significantly enhance the growth of PEDOT. Electrochemical quartz crystal microbalance (EQCM) analysis was performed to study the mass changes in the electrode during the electrodeposition of PEDOT, with and without the addition of FAD. The optimal cycle number for preparing the modified electrode was determined to be 9, and the corresponding surface coverage of FAD (ΓFAD) was ca. 5.11×10−10molcm−2. The amperometric detection of iodate was performed in a 100mM buffer solution (pH 1.5). The GCE/PEDOT/FAD showed a sensitivity of 0.78μAμM−1cm−2, a linear range of 4–140μM, and a limit of detection of 0.16μM for iodate. The interference effects of 250-fold Na+, Mg2+, Ca2+, Zn2+, Fe2+, Cl−, NO3−, I−, SO42− and SO32−, with reference to the concentration of iodate were negligible. The long-term stability of GCE/PEDOT/FAD was also investigated. The GCE/PEDOT/FAD electrode retained 82% of its initial amperometric response to iodate after 7 days. The GCE/PEDOT/FAD was also applied to determine iodate in a commercial salt.

Determination of iodate in food, environmental, and biological samples after solid-phase extraction with Ni-Al-Zr ternary layered double hydroxide as a nanosorbent.

Nanostructured nickel-aluminum-zirconium ternary layered double hydroxide was successfully applied as a solid-phase extraction sorbent for the separation and pre-concentration of trace levels of iodate in food, environmental and biological samples. An indirect method was used for monitoring of the extracted iodate ions. The method is based on the reaction of the iodate with iodide in acidic solution to produce iodine, which can be spectrophotometrically monitored at 352 nm. The absorbance is directly proportional to the concentration of iodate in the sample. The effect of several parameters such as pH, sample flow rate, amount of nanosorbent, elution conditions, sample volume, and coexisting ions on the recovery was investigated. In the optimum experimental conditions, the limit of detection (3s) and enrichment factor were 0.12 μg mL−1 and 20, respectively. The calibration graph using the preconcentration system was linear in the range of 0.2–2.8 μg mL−1 with a correlation coefficient of 0.998. In order to validate the presented method, a certified reference material, NIST SRM 1549, was also analyzed.

OPTIMIZATION OF PARAMETERS FOR THE SYNTHESIS OF SILVER IODATE SUBMICRON BELTS BY TAGUCHI ROBUST DESIGN METHOD

A statistical experimental design method was implemented to optimize experimental conditions for the preparation of silver iodate fine belts using precipitation method. Ultrafine silver iodate belts were synthesized by addition of silver ion solution to the iodate reagent. The optimal conditions were determined using the Taguchi method. The effect of reaction conditions such as silver and iodate concentrations, flow rate of reagent addition, and temperature on the diameter of synthesized silver iodate belts were investigated. The results for analysis of variance (ANOVA) showed that silver iodate submicron belts can be synthesized by controlling silver concentration, flow rate, and temperature. Finally, the optimum conditions for synthesis of silver iodate submicron belts by this simple and fast method were proposed. The results of ANOVA showed that 0.001 mol/L silver ion concentration, 10 mL/min flow rate for addition of iodate reagent to the solution, and 0°C temperature are optimum conditions for producing silver iodate submicron belts with 228 ± 32 nm width.

Concentration-Dependent Mobility, Retardation, and Speciation of Iodine in Surface Sediment from the Savannah River Site

Iodine occurs in multiple oxidation states in aquatic systems in the form of organic and inorganic species. This feature leads to complex biogeochemical cycling of stable iodine and its long-lived isotope, (129)I. In this study, we investigated the sorption, transport, and interconversion of iodine species by comparing their mobility in groundwaters at ambient concentrations of iodine species (10(-8) to 10(-7) M) to those at artificially elevated concentrations (78.7 μM), which often are used in laboratory analyses. Results demonstrate that the mobility of iodine species greatly depends on, in addition to the type of species, the iodine concentration used, presumably limited by the number of surface organic carbon binding sites to form covalent bonds. At ambient concentrations, iodide and iodate were significantly retarded (K(d) values as high as 49 mL g(-1)), whereas at concentrations of 78.7 μM, iodide traveled along with the water without retardation. Appreciable amounts of iodide during transport were retained in soils due to iodination of organic carbon, specifically retained by aromatic carbon. At high input concentration of iodate (78.7 μM), iodate was found to be reduced to iodide and subsequently followed the transport behavior of iodide. These experiments underscore the importance of studying iodine geochemistry at ambient concentrations and demonstrate the dynamic nature of their speciation during transport conditions.

Preliminary Evidence for Iodate Reduction in Bottom Waters of the Gulf of Mexico During an Hypoxic Event

The distributions of iodate and total inorganic iodine concentrations in the waters on the Texas–Louisiana shelf in April, June, and August 2004 are described. Iodine–salinity graphs show three-end-member mixing involving onshore and offshore surface waters and deep offshore water. The April survey showed simple mixing on the surface, but in the later surveys, iodate concentrations were often much lower than predicted by the mixing curve while those for total inorganic iodine were higher. This demonstrated both iodate reduction in the water and iodide addition, although individual samples did not show equivalent speciation changes. Hydrographically, the system consists of the estuaries of the Mississippi and Atchafalaya rivers as they spill onto the shelf. The waters are stratified seasonally by a robust halocline, leading to hypoxia in the bottom waters from the combined effect of restricted downward diffusion of oxygen and the sinking of the luxuriant growth of phytoplankton induced by riverine nutrient supply. The distributions of iodate and total inorganic iodine are, therefore, interpreted in terms of water–sediment interaction as the shelf shoals to the north.

Distribution of iodide and iodate in the Atlantic sector of the southern ocean during austral summer

The biogeochemistry of iodine in the waters of the Atlantic sector of the Southern Ocean was investigated during the Polarstern cruise ANTXXIV-3 ZERO&DRAKE. The speciation and distribution of iodine (iodate and iodide) in seawater was examined across gradients of iron concentrations and phytoplankton abundance, ranging from an open ocean region along the Zero Meridian to the Weddell Sea and Drake Passage. Iodine cycling in high latitudes differs from that in low latitudes due to differences in the plankton community composition and the physicochemical characteristics. Iodate concentrations ranged between 400 and 450 nmol L −1 from the surface to the bottom. Surface concentrations of iodide (17 to over 60 nmol L −1) were about an order of magnitude higher than below the pycnocline. The peak values of iodide lay nearly always within the euphotic zone and showed a weak, positive correlation with nitrite concentrations in the upper 200 m. In all vertical profiles a pronounced sub-surface maximum in iodide appears between 50 and 200 m depth indicating an iodide drawdown at the near surface. Iodide distribution in the Weddell Sea showed elevated levels in Weddell Sea Bottom Water (WSBW) indicating slow oxidation kinetics and the potential for iodide as a tracer of WSBW formation.

A Novel Approach for the Simultaneous Determination of Iodide, Iodate and Organo-Iodide for 127I and 129I in Environmental Samples Using Gas Chromatography−Mass Spectrometry

In aquatic environments, iodine mainly exists as iodide, iodate, and organic iodine. The high mobility of iodine in aquatic systems has led to (129)I contamination problems at sites where nuclear fuel has been reprocessed, such as the F-area of Savannah River Site. In order to assess the distribution of (129)I and stable (127)I in environmental systems, a sensitive and rapid method was developed which enables determination of isotopic ratios of speciated iodine. Iodide concentrations were quantified using gas chromatography-mass spectrometry (GC-MS) after derivatization to 4-iodo-N,N-dimethylaniline. Iodate concentrations were quantified by measuring the difference of iodide concentrations in the solution before and after reduction by Na(2)S(2)O(5). Total iodine, including inorganic and organic iodine, was determined after conversion to iodate by combustion at 900 °C. Organo-iodine was calculated as the difference between the total iodine and total inorganic iodine (iodide and iodate). The detection limits of iodide-127 and iodate-127 were 0.34 nM and 1.11 nM, respectively, whereas the detection limits for both iodide-129 and iodate-129 was 0.08 nM (i.e., 2pCi (129)I/L). This method was successfully applied to water samples from the contaminated Savannah River Site, South Carolina, and more pristine Galveston Bay, Texas.

A Multilayer Film for Bifunctional Electrocatalyst and Electrochemical Sensor Based on Polyoxometalate and Tris(1,10-Phenanthroline)Ruthenium

The multilayer films containing tris(1,10-phenanthroline) ruthenium(II) Ru(phen)3Cl2 (abbr. Ru(phen)3, phen = 1,10-phenanthroline) and polyoxometalate [P2W18O62]6− (abbr. P2W18) through a layer-by-layer (LBL) process were fabricated. UV–vis absorption spectra showed that the subsequent growth of the multilayer film was regular and highly reproducible from layer to layer. X-ray photoelectron spectra (XPS) confirmed the incorporation of Ru(phen)3 and P2W18 into the film. The result of atomic force microscopy (AFM) revealed a relatively uniform surface morphology of the multilayer film. The multilayer film exhibited remarkable electrocatalytic activities toward the reduction of $$ {\text{IO}}_{3}^{ - } $$ and the oxidation to l-cysteine. The value of I pc was as a function with the concentration of iodate and l-cysteine, which indicated that the film can be a candidate for bifunctional electrocatalyst and electrochemical sensor.

Determination of iodide and iodate in edible salt by ion chromatography with integrated amperometric detection

Iodised salt compositions formulated with potassium iodate typically have iodate content of 20–40 ppm (μg/g) which translates to iodine content of 15–30 ppm. The technique of iodide estimation in brine by ion chromatography with amperometric detection was applied to iodate estimation in salt. The method involved reduction of iodate to iodide with excess sodium bisulphite followed by estimation of iodide. No other pre-treatment was necessary for iodate estimation in the concentration range of interest for iodised salt. Quantitative analysis was feasible for iodate concentrations ⩾5 ppm in salt. Iodised salt formulations containing iodide and iodate together were also analysed and the two constituents were quantified separately. Interferences from impurities normally present in salt were insignificant. An important advantage of the present method is that it eliminates the possibility of misleading results from potential adulterants which can impart positive iodometric test while, at the same time, keeping the analytical procedure simple.

Intensive sampling of iodine and nutrient speciation in naturally eutrophicated anchialine pond (Rogoznica Lake) during spring and summer seasons

A study of inorganic iodine speciation in the water column of a naturally eutrophicated anchialine pond (Rogoznica Lake, East Adriatic Coast) was conducted in a period between April and July 2004 to obtain information how close the inorganic iodine system is to that of inorganic nutrients during spring, when phytoplankton activity is at maximum, and how the system changes up to summer, when highly reducible redox-conditions prevail in deep water. Iodate and iodide concentrations were determined by differential pulse voltammetry and cathodic stripping square wave voltammetry, respectively. In addition, total iodine concentrations were determined by ICP-MS in May. The hydrographic and nutrient profiles indicate that the system was greatly affected by photosynthesis and demonstrate strong seasonal change in predominant phytoplankton assemblages. The hypolimnion depths were dominated by regeneration processes and benthic influence, with anoxic and sulphidic conditions at maximum sampling depth in July. The iodine profiles show no clear direct relationship between the iodine and nutrient system regarding to the phytoplankton production. Meanwhile, the results demonstrate temporal matching between high iodate and high regenerated nitrate concentrations in the surface layers, and close spatial matching of iodate production and nitrification at mid-depths of hypolimnion. The key role of nitrifers is discussed and the implication of these findings is explored.

Iodine oxidation by hydrogen peroxide in acidic solutions, Bray-Liebhafsky reaction and other related reactions

The kinetics of the iodine oxidation by hydrogen peroxide is a complicated function of the concentrations of iodine, hydrogen peroxide, perchloric acid and iodate. A proposed model in eight steps explains the new experimental results. It explains also the effect of the concentrations at the steady state of the hydrogen peroxide decomposition catalyzed by iodine and iodate. Without iodate added initially, the iodine oxidation by hydrogen peroxide is preceded by an induction period that depends on the oxygen concentration. A simple extension of the proposed model gives a semi-quantitative explanation of the oxygen effect and allows simulations of the Bray-Liebhafsky oscillations at 25 degrees C.

Seasonal and interannual variation of dissolved iodine speciation at a coastal Antarctic site

Dissolved iodine speciation in surface seawater at a coastal Antarctic site has been studied over a period spanning three austral summers. The sampling site is biologically productive, with a summertime algal bloom accompanying strong seasonal variations in physical and chemical parameters. The results suggest a seasonal cycle in which iodide concentrations increase and iodate concentrations decrease during the summer, though the magnitude of these changes appears to be subject to considerable interannual variability. Iodide concentrations were typically very low, with minimum values of 10 to 20 nM at the beginning and end of the ice-free summer periods and summertime maxima of about 35 nM in 2005/06, 150 nM in 2006/07 and 82 nM in 2007/08. More detailed observations of iodide and iodate concentrations made during summer 2005/06 demonstrated that the accumulation of iodide was strongly correlated with integrated biological primary productivity, with an implied I/C assimilation ratio of 1.6 × 10 −4.

LDH modified electrode for sensitive and facile determination of iodate

A number of studies have shown that Layered double hydroxides, LDH, are attractive materials for fabrication of biosensors. However, few studies have addressed the application of LDH modified electrodes for sensing of electroactive anions. In this study, we used synthetic Zn–Al LDH to construct a modified gold electrode for amperometric detection of iodate. The modified electrodes showed higher electrocatalytic activity toward reduction of iodate in pH 6.5 phosphate buffer solution. Amperometry revealed that the stable-state current is linear with the iodate concentration in the range of 1–2000 μM with the detection limit of 0.25 μM. The sensor was applied to detect iodate in analysis of real samples, such as iodized table salt and kelp. Low cost, high sensitivity, fast amperometric response time, wide linear concentration range, excellent stability, good selectivity and easy preparation are great advantage of this electrode.

Winkler's method overestimates dissolved oxygen in seawater: Iodate interference and its oceanographic implications

Dissolved oxygen in seawater has been determined by using the Winkler's reaction scheme for decades. An interference in this reaction scheme that has been heretofore overlooked is the presence of naturally occurring iodate in seawater. Each mole of iodate can result in an apparent presence of 1.5 mol of dissolved oxygen. At the concentrations of iodate in the surface and deep open ocean, it can lead to an overestimation of 0.52 ± 0.15 and 0.63 ± 0.05 μmol kg − 1 of oxygen in these waters respectively. In coastal and inshore waters, the effect is less predictable as the concentration of iodate is more variable. The solubility of oxygen in seawater was likely overestimated in data sources that were based on the Winkler's reaction scheme for the determination of oxygen. The solubility equation of García and Gordon [Garcia H.E., Gordon, L.I., 1992. Oxygen solubility in seawater: Better fitting equations. Limnol. Oceanogr. 37, 1307–1312] derived from the results of Benson and Krause [Benson, F.B., Krause, D. Jr., 1984. The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere. Limnol. Oceanogr. 29, 620–632] is free from this source of error and is recommended for general use. By neglecting the presence of iodate, the average global super-saturation of oxygen in the surface oceans and the corresponding efflux of oxygen to the atmosphere both have been overestimated by about 8%. Regionally, in areas where the degree of super-saturation or under-saturation of oxygen in the surface water is small, such as in the tropical oceans, the net air–sea exchange flux can be grossly under- or overestimated. Even the estimated direction of the exchange can be reversed. Furthermore, the presence of iodate can lead to an overestimation of the saturation anomaly of oxygen in the upper ocean attributed to biological production by 0.23 ± 0.07%. AOU may have been underestimated by 0.52 ± 0.15 and 0.63 ± 0.05 μmol kg − 1 in the surface mixed layer and deep water, while preformed phosphate and preformed nitrate may have been overestimated by 0.004 ± 0.001 and 0.06 ± 0.02 μmol kg − 1 in the surface mixed layer, and 0.005 ± 0.0004 and 0.073 ± 0.006 μmol kg − 1 in the deep water. These are small but not negligible corrections, especially in areas where the values of these parameters are small. At the increasing level of sophistication in the interpretation of oxygen data, this source of error should now be taken into account. Nevertheless, in order to avoid confusion, an internationally accepted standard needs to be adopted before these corrections can be applied.

Flow Injection Determination of Vitamin C in Pharmaceutical Preparations by Differential Electrolytic Potentiometry

Differential electrolytic potentiometry (DEP) was coupled with Flow injection analysis (FIA) technique for the determination of ascorbic acid in pharmaceutical preparations. Platinum electrodes were used as an indicating system to follow the oxidation of vitamin C with either potassium iodate, or potassium permanganate in an acidic medium. Univariate method was employed to optimize the variables such as the current density, the flow rate, the concentrations of the oxidants and the sulfuric acid. A current density of 40 μAcm -2 and a flow rate of 25 μlsec -1 were found to be optimum. The optimum concentrations of iodate and permanganate were 8.35 mM and 0.11 mM respectively. On using iodate as an oxidant the method showed a linear range of 12-130 μgml -1 , a detection limit of 9 μgml -1 and R2 of 0.999. In case of permanganate a linear range of 18-36 μgml -1 , a detection limit of 11 μgml -1 and an R2 of 0.996 were obtained. The procedure was applied successfully to the determination of vitamin C in commercial tablets. The results of this study were found to be statistically comparable with those obtained by official methods.

Photocatalytic production of oxygen in a dual bed system using a reversible redox mediator on Ir-TiO2 catalyst

Photocatalytic O2 evolution by water splitting in an alkaline solution with a redox mediator was investigated in a dual bed system configuration: one bed was used for oxygen evolution and the other for hydrogen evolution. The employed photocatalyst was Ir-TiO2 and the iodate ion, KIO3, was used as a redox mediator. In order to find the optimum conditions for oxygen evolution, the effect of alkaline concentration, KIO3 concentration and the amount of Ir loading on the photocatalytic reactivity was examined in an irradiation area of 0.055 m2 reactor with a 400 W U.V. lamp. The experimentally obtained results showed that oxygen evolution depends on the concentration of the alkaline solution, the potassium iodate concentration and the amount of Ir loading.

Electrocatalytic thin films based on nordihydroguaiaretic acid-functionalyzed polyaniline

A novel composite, polymeric material can be obtained by potential cycling of polyaniline (PANI)-modified electrode in the presence of nordihydroguaiaretic acid (NDGA). As a consequence, the properties of PANI change from those of a conducting polymer to those of a redox polymer. Thus formed composite PANI–NDGA films show redox activity characterized by two new electrochemical couples observed at mid-peak potentials of 0.32 and 0.52 V (vs. Ag/AgCl, 0.5 M H 2SO 4). The peak currents exhibit a linear dependence on the potential scan rate as expected for surface-confined redox species and the peak potentials shift toward lower potentials with increasing solution pH at a rate of ca. 60 mV/pH unit. The PANI–NDGA composite film was found to electrocatalyze the reduction of iodate in acidic (pH 1.8) Britton–Robinson buffer. The modified electrode could be applied as an amperometric sensor for iodate. A linear dependence between the reduction current and iodate concentration was observed over the range of 1–100 μM with a detection limit of 0.05 μM. The observed restructuring of PANI in the presence of NDGA was confirmed by AFM imaging and FT-IR spectroscopy.

Solubility of sodium and potassium iodates in saturated salt solutions

The determination of the solubilities of KIO 3 and NaIO 3 in saturated NaCl solution at 0, 10, 20 °C were carried out in two ternary systems KIO 3–NaCl–H 2O and NaIO 3–NaCl–H 2O. Saturated KIO 3 and NaIO 3 solutions were prepared and NaCl was added to saturation. Iodate concentrations were measured using standardized sodium thiosulphate. The solubilities of KIO 3 and NaIO 3 are temperature sensitive over the range 0 °C to 20 °C (unlike NaCl). Iodate solubility was much lower in saturated NaCl than that of deionised water. In saturated NaCl at 10 °C, for example, NaIO 3 was 19% and KIO 3 was 15% the solubility of that found in deionised water at the same temperature.