Iodide In Water Samples Research Articles

Determination of iodide and total iodine in estuarine waters by cathodic stripping voltammetry using a vibrating silver amalgam microwire electrode

Iodide in natural waters is an important nutrient to aquatic organisms and its determination is of relevance to marine aquaculture. For this reason it is of interest to have a simple analytical method for determination of iodide in water samples. Iodide in seawater can be determined electrochemically by cathodic stripping voltammetry (CSV) with a mercury drop electrode which has environmental drawbacks. In an attempt to minimise the use of mercury in voltammetry, a vibrating silver amalgam microwire electrode is used here for the determination by CSV of iodide speciation in natural waters including seawater. Microwire electrodes were made from silver wires (diameter: 12.5µm) and electrochemically coated with mercury. The electrode surface was stable for extended periods of analyses (at least one week) and was then replaced. The optimised conditions include a pH 8, a frequency of 500Hz and a deposition time of 60s, among others. The microwire was reactivated between scans using a conditioning potential at −3 V for 1s. The detection limit for iodide in seawater was found to be 0.7nM I- at a deposition time of 60s. The response increased linearly with the concentration of iodide in seawater up to 100nM I-. The method was successfully applied to various samples from the estuary of the river Mersey (Liverpool Bay). An existing procedure for iodine speciation was modified to enable determination of iodate and total iodine as well as iodide in estuarine waters.

Unmodified gold nanoparticles for in-drop plasmonic-based sensing of iodide

This work reports on the applicability of unmodified citrate-protected gold nanoparticles (AuNPs) obtained by the Turkevich-Frens method as nanoprobes for iodide detection. The colorimetric assay is based on the red-shift of the gold localized surface plasmon resonance (LSPR), which is produced when a microvolume of AuNPs interacts with vapor iodine. The method involves in situ iodine formation, transfer of the volatile to the headspace and its trapping/enrichment into a microdrop of citrate-capped AuNPs. The combination of a three phase microseparation approach with a cuvetteless microvolume UV–vis spectrophotometric system enables the determination of iodide with an almost negligible consumption of colloidal gold solution and improved selectivity without the need of any functionalization. Remarkably, the addition of small amounts of organic modifiers significantly improves the sensitivity of the assay. A limit of detection of 0.30μM iodide and a repeatability of 4.7% (N=8) were obtained. Furthermore, the colorimetric probe was successfully applied to the detection of iodide in water samples with recoveries in the range 91.9–104.5%.

Comparison of two novel in-syringe dispersive liquid–liquid microextraction techniques for the determination of iodide in water samples using spectrophotometry

Two new, rapid methodologies have been developed and applied successfully for the determination of trace levels of iodide in real water samples. Both techniques are based on a combination of in-syringe dispersive liquid–liquid microextraction (IS-DLLME) and micro-volume UV–Vis spectrophotometry. In the first technique, iodide is oxidized with nitrous acid to the colorless anion of ICl2- at high concentration of hydrochloric acid. Rhodamine B is added and by means of one step IS-DLLME, the ion-pair formed was extracted into toluene and measured spectrophotometrically. Acetone is used as dispersive solvent. The second method is based on the IS-DLLME microextraction of iodide as iodide/1, 10-phenanthroline-iron(II) chelate cation ion-pair (colored) into nitrobenzene. Methanol was selected as dispersive solvent. Optimal conditions for iodide extraction were determined for both approaches. Methods are compared in terms of analytical parameters such as precision, accuracy, speed and limit of detection. Both methods were successfully applied to determining iodide in tap and river water samples.

Nanoelectrode ensembles for the direct voltammetric determination of trace iodide in water

Procedures for the preparation and characterisation of ensembles of gold nanodisk electrodes (NEE) of 30 nm diameter are presented, in particular focusing on improvements in the signal/background current ratios and detection limits with respect to the electrochemical oxidation of iodide and its analytical determination in water samples. At NEEs iodide undergoes a quasi-reversible diffusion controlled oxidation with a slight shift in E 1/2 values and slightly higher peak to peak separation with respect to conventional gold disk electrodes. The double layer charging current at the NEE is significantly lower than at conventional electrodes so that the detection limit (DL) by cyclic voltammetry with NEEs in tap water is significantly lower than DL at the Au-disk millimetre-sized electrode (DL 0.3 µM at NEE vs. 4 µM for Au-disk). Finally, it is shown that NEEs in combination with square wave voltammetry can be applied for the direct determination of iodide in water samples from the lagoon of Venice, with a detection limit of 0.10 µM.

Preparation of a Novel Iodide-Selective Electrode Based on Iodide-Miconazole Ion-Pair and Its Application to Pharmaceutical Analysis

An iodide-miconazole ion-paired complex was used as a suitable ion-exchanger for the preparation of a plasticized-PVC membrane electrode. Among different solvent mediators tested, dioctylsebacate exhibited the proper response characteristics, including Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of -59.8 +/- 0.5 mV decade(-1) for I- ion over a concentration range of 1.0 x 10(-5) - 1.0 x 10(-2) M with a limit of detection of 7.0 x 10(-6) M. The electrode displays a good selectivity for I- with respect to a number of inorganic and organic species. It canbe used over a pH range of 2.5 - 8.5. The membrane sensor was successfully applied to the determination of iodide in water samples and blood serum, as well as in pharmaceutical products such as iodoquinol and thyroxin.

Flow Injection–Spectrophotometric Determination of Trace Amounts of Bromide by Its Catalytic Effect on the 4,4′-Bis(dimethylamino)diphenylmethane–Chloramine T Reaction

A flow injection analysis method is proposed for the spectrophotometric determination of trace amounts of iodide based on its catalytic effect on the oxidation of 4, 4′-bis(dimethylamino)diphenylmethane (tetrabase) by Chloramine T in a weakly acidic solution. Iodide in water samples can be determined at a sampling rate of 85 h-1 with 300μl sample injections. The detection limit is 0.1μg l-1 and the calibration graph for iodide is linear up to 2μg l-1, showing a slightly negative deviation in the higher concentration range. The relative standard deviations are 2.8 and 0.8% for 0.40 and 4.0μg l-1 iodide, respectively. Although free iodine shows a somewhat lower catalytic effect and iodate no catalytic effect up to at least 50μg l-1 as iodine, these species show the same effect as iodide upon being reduced with thioacetamide in an acidic solution. The procedure has been applied to the determination of iodide in natural water samples as well as iodine impurity in both distilled and redistilled water samples. It has also been used to examine iodine contamination in ambient air.