Iodine in seawater

Truesdale [77] has described autoanalyser procedures for the determination of iodate and total iodine in seawater. The total iodine content of seawater (approximately 50-60 ig/l) is believed to be composed of iodate (30-60 xg/l of I) and iodine-iodine (0-20 xg/l) with perhaps a few ig/l of organically... 

Schnepfe [83] has described yet another procedure for the determination of iodate and total iodine in seawater. To determine total iodine 1 ml of 1% aqueous sulfamic acid is added to 10 ml seawater which, if necessary, is filtered and then adjusted to a pH of less than 2.0. After 15 min, 1 ml sodium hydroxide (0.1 M) and 0.5 ml potassium permanganate (0.1M) are added and the mixture heated on a steam bath for one hour. The cooled solution is filtered and the residue washed. The filtrate and washings are diluted to 16 ml and 1ml of a phosphate solution (0.25 M) added (containing 0.3 xg iodine as iodate per ml) at 0 °C. Then 0.7 ml ferrous chloride (0.1 M) in 0.2% v/v sulfuric acid, 5 ml aqueous sulfuric acid (10%) - phosphoric acid (1 1) are added at 0 °C followed by 2 ml starch-cadmium iodide reagent. The solution is diluted to 25 ml and after 10-15 min the extinction of the starch-iodine complex is measured in a -5 cm cell. To determine iodate the same procedure is followed as is described previously except that the oxidation stage with sodium hydroxide - potassium permanganate is omitted and only 0.2 ml ferrous chloride solution is added. A potassium iodate standard was used in both methods. 

Kesari et al. [8] have recently described a sensitive spectrophotometric method for determining iodine in seawater. 

In environmental waters, the most important oxidation states are iodide ( — 1) and iodate ( + 5). Most published methods for the analysis of radioiodine aim only to convert all species to one chemical form in order to determine a total concentration value for the particular nuclide of interest. However, some specialist methods designed for the analysis of the stable element such as that recently described by Woittiez et al. (1991) for the determination of iodide, iodate, total inorganic iodine and charcoal-absorbable (organic) iodine in seawater could presumably be adapted to provide information about the speciation of radioiodine as well. More difficult to adapt would be techniques such as polarography which have been useful in the measurement of the iodide/iodate system (e.g. Liss et al., 1973). 

Figure 1.1 The main pathways for iodine present in the sea to enter into the human food chain. Seawater is a huge reservoir of iodine, and it may suppiy iodine to humans using severai pathways. The main speciations of iodine in seawater are iodide (i ) and iodate (iOT).

The determination of iodine in seawater helps in understanding the marine environment. A variety of analytical methods have been proposed for the quantitative determination of iodine in seawater. This chapter discusses the methods employed for the separation and determination of iodine in seawater. These methods include capillary electrophoresis (CE), ion chromatography (IC), high-performance hquid chromatography (HPLC), gas chromatography (GC), spectrophotometry, ion-selective electrode, polar-ography, voltammetry, atomic emission spectrometry (AES), and neutron activation analysis (NAA). The advantages and hmitations of these methods are also assessed and discussed. Since iodine is present in the ocean at trace levels and the matrices of seawater are complex, especially in estuarine and coastal waters, the methods developed for the... 

Another method developed for the determination of iodide was GC—mass spectrometry (Mishra et al., 2000). Iodide was oxidated to iodine with 2-iodosobenzoate, and then converted into d-iodo-A. A dimethylanifine in the presence of A, A -dimethylanihne. The derivative was extracted into cyclohexane and determined by GC—mass spectrometry. The method could also be used to determine iodine by derivatization in the absence of 2-iodoso-benzoate, and iodate by its reduction with ascorbic acid to iodide and subsequent derivatization. The calibration graph was finear from 0.02 to 50p,g U of iodide with a correlation coefficient of 0.9998. The limit of detection was 8ng 1 of iodide. The proposed method was appfied to the determination of iodate in iodized table salt and free iodide and total iodine in seawater. The recovery was in the range of 96.8—104.3%, and the relative standard deviations were from 1.9% to 3.6%. A sample clean-up by solid-phase extraction with a LiChrolut EN cartridge was... 

Figure 1.7 Chromatogram of iodate and iodide in seawater by nonsuppressed 1C with inductively coupled plasma mass spectrometric detection. The main speoiation of iodine in seawater, iodate (IO3) and iodide (l ), could be determined simultaneously. Conditions column, Agilent G3154A/101 (150 X 4.6 mm inner diameter) column temperature = 20°C injection volume = 10(il mobile phase, 20.0mmol 1 of NH4NO3 at pH 5.6 flow rate = 1.0ml min The ICP-MS conditions flow rate of plasma gas (Ar) = 151 min flow rate of auxiliary gas (Ar) = 1.01- min flow rate of oarrier gas (Ar) = 1.151- min sampling depth = 7.5mm integration time = 1 s dwell time = 0.5s. The 2 1 was seleoted for deteotion by single-ion monitoring mode. Reprinted from Chen etal., (2007) with permission from Elsevier.

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