**4.1.3 Foodstuffs**

382 Macro to Nano Spectroscopy

An alternative flow injection spectrophotometric method for the determination of I- in the ground and surface water was reported by Kamavisdar and Patel (Kamavisdar & Patel, 2002). The method was based on the catalytic destruction of the colour of the Fe(III)–SCN−– CP+–nBPy quarternary complex. The detection limit of the method was reported to be 0.1 ng ml−1 of iodide. Another redox reaction between chloramine-T and N,N' tetramethyldiaminodiphenylmethane (Feigl's Catalytic Reaction) was applied for the

An alternative to the Sandell-Kolthoff method was developed by Gurkan et al., (Gurkan et al., 2004). Iodides were determined in waters by inhibition kinetic spectrophotometric method based on the inhibitory effect of I- on the Pd(II)-catalyzed reduction of Co(III)-EDTA by the hypophosphite ion in a weak acid medium. The main advantage of this method was related to the pretreatment step of the analysis which would be omitted (a time-consuming alkaline ashing preparative procedure is necessary in order to apply the standard method). The sensitivity of the method allowed determinations in the range of 2-35 ng/ml of I*−* (LOD=1.2 ng/ml). Koh et al. (Koh et al., 1988) separated I- from other chemical species by its oxidation and subsequent extraction into carbon tetrachloride. The proposed spectrophotometric method was based on the extraction of the back-extracted iodide into 1,2-dichloroethane as an ion pair with methylene blue. The authors applied that method to determine various amounts of iodide in natural water samples (at the 10–6 mol l–1 level). Spectrophotometric determination of the total dissolved sulfide in natural waters allowed also simultaneous determination of

Different analytical techniques have been developed to extract and measure iodine concentration from the soil. The reduction of Ce (IV) by As (III) catalyzed by iodine can be used to determine the low concentration of iodine in plant and soil samples. The sample preparation requires a specialized combustion apparatus and trapping systems for iodine. For plant samples and biological materials, halogen extraction using TMAH under mild

Kesari et al. (Kesari et al., 1998) developed a simple and sensitive spectrophotometric method for the determination of iodine in tap water, sea water, soil, iodized salt and pharmaceuticals samples. The said method was based on oxidation of I- to IO3- with bromine

with leuco crystal violet and the crystal violet dye liberated shows maximum absorbance at 591 nm. Beer's law is obeyed over the concentration range from 0.04 to 0.36 mg/l of iodine in a final solution volume of 25 ml. The method is free of interference of other major

Lu et al. (Lu et al. 2005*)* applied the arsenic-cerium redox method for assessment of iodine content in soils and waters. Mean iodine concentration in soil samples was found to be 1.32 ± 0.14 mg/kg, and its content correlated positively with the water iodine content. In association with the photometric analytical technique, the alkaline dry ashing method (adding KOH and ZnSO4), along with digestion via the calorimetric bomb and the utilization of the Schoniger digestion arc, provide a means for obtaining reliable results. For this investigation, the influence of iodine fertilisation on the iodine concentration of cress

by addition of KI in acidic medium. I2 is then reacted

determination of traces of iodine in drinking water (Jungreis & Gedalia, 1960).

other UV-absorbing ions, including I- (Guenther et al., 2001).

conditions has proved to be effective (Knapp et al., 1998).

**4.1.2 Soil and plant samples** 

water and liberation of free I2 from IO3-

toxicants.

A semi-automated method for determination of the total iodine in milk was described by Aumont (Aumont, 1982). The method involved destruction of organic matter by alkaline incineration and automated spectrophometric determination of iodide based on the Sandell and Kolthoff's reaction. The recoveries of the added iodide before calcination were between 90.05 +/- 7.36% and 97.14 +/- 4.56% (mean +/- S.D.). The coefficient of variation ranged from 2.15 to 7.21% depending on the iodine content in the milk. The limit of detection was estimated to be around 2 µg/kg.

The iodide-catalyzed reaction between As(III) and Ce(IV) stopped by the addition of diphenylamine-4-sulfonic acid was used for the development of a sensitive kinetic procedure for determining iodides with a detection limit of 2 ng/mL. The developed procedure was suitable for the determination of the total iodine in foodstuffs (Trokhimenko & Zaitsev, 2004).

Another modification of the catalytic kinetic spectrophotometric method has been established for the determination of iodine using the principle that potassium periodate oxidize rhodamine B (RhB) to discolor and I− has a catalytic effect on the reaction. The absorbance difference (ΔA) is linearly related with the concentration of iodine in the range of 0 – 2.6 µg/mL and fits the equation ΔA = 0.1578 C(C: μg/mL) + 0.0052, with a regression coefficient of 0.9965. The detection limit of the method is 7.10 ng/mL. The method was used to determine iodine in kelp, potato, tap water, and rain water samples. The relative standard deviation of 13 replicate determinations was 1.81–2.10%. The recovery of the standard addition of the method was 96.2–99.2% (Zhai et al., 2010).

Some researchers reported that the spectrophotometric methods for the determination of IO3 - are based on its reaction with the excess I- to liberate I2 which forms tri iodide (Afkhami & Zarei 2001; Ensafi & Dehaghi, 2000).

Balasubramanian and Nagaraja (Balasubramanian & Nagaraja, 2008) described a sensitive spectrophotometric method for the determination of multiple iodine species such as I- , I2, IO3- and IO4-. The method involved oxidation of iodide to ICl2- in the presence of iodate and chloride in an acidic medium. The formed ICl2- bleaches the dye methyl red. The decrease in the intensity of the colour of the dye is measured at 520 nm. Beer's law is obeyed in the concentration range 0-3.5 μg of iodide in an overall volume of 10 ml. The relative standard deviation was 3.6% (n=10) at 2 μg of iodide. The developed method can be applied to the samples containing iodine, iodate and periodate by prereduction to iodide using Zn/H(+) or NH2NH2/H(+). The effect of interfering ions on the determination was pointed out. The described method was successfully applied to determine iodide and iodate in salt samples and iodine in pharmaceutical preparations.

Silva *et al. (*Silva et al., 1998) outlined a new method for the determination of iodate in table salt. KIO3, after being converted to I3 by reacting with iodide in the presence of phosphoric

A Review of Spectrophotometric and Chromatographic Methods

& Santschi, 2003). The IC method can separate I-

platinum and glass carbon electrodes.

interference to the absolute minimum.

**4.2.1 Water samples** 

seawater with high content of Cl-

and Sample Preparation Procedures for Determination of Iodine in Miscellaneous Matrices 385

modern analytical laboratory. Fast, simple, reliable and sensitive chromatographic systems coupled with various detectors became the basic tool in many analytical laboratories. Routine analysis of iodine compounds can be carried out by means of gas chromatography (GC) and high performance liquid chromatography (HPLC). Analysis of inorganic iodine species in waters is mainly carried out with the use of ion chromatography (IC) or IC inductively coupled-mass spectrometry (IC-MS). Separation methods enable direct determination of various species of iodine in the presence of various kinds of complex components with the detection limit in the range of sub μg/l or µg/l (Hu et al., 1999; Schwer

while HPLC method usually uses the reverse phase column modified by an ionpairing reagent in the mobile phase. Both spectrophotometric and electrochemical detectors are commonly used. Pulsed amperometric detection (PAD) typically utilizes gold, silver,

It has to be emphasized that both spectrophotometric and chromatographic methods are not applicable to a wide range of matrices. As far as complex matrices are concerned (e.g.

tools for iodine determination. Unfortunately, none of these methods are flexible enough to measure all iodine species, including organo-iodine in biological samples. The oxidative pretreatment of biological materials limits the application of the described methods (IO3- and I- can be converted to I2 under acidic conditions). In order to analyse IO3- , I-, and organic forms of iodine in the same sample, IC is often coupled with ICP-MS. What is more, the coupling of highly efficient IC to multi-dimensional detectors such as MS or ICP/MS significantly increases sensitivity, while simultaneously reducing possible matrix

Liang et al. (Liang et al., 2005) applied the disposable electrode for the determination of iodide in soil and seawater samples with the spiked recovery ranging from 96–104% and the detection limit of 0.5 μg/L. Rong et al. (Rong et al., 2005) performed a direct determination of iodide and thiocyanate ions in seawater collected from the coasts of Japan. No sample pretreatment was needed. Liquid chromatography (LC) with a UV detection of 220 nm was applied. The separation was achieved on a C30 column of conventional size (150 mm × 4.6 mm i.d.) modified with poly(ethylene glycol). Such stationary phase enables the

others. An aqueous solution of 300 mM sodium sulfate and 50 mM sodium chloride was used as the mobile phase. Detection limits (S/N=3) were obtained by injecting a 20-μL

Buchberger (Buchberger, 1988) determined I- (among other ions) in water samples using an anion-exchange stationary phase (Vydac 302-IC) and methanesulphonic acid solution as the mobile phase. A post-column reaction detector was developed based on the reaction between iodide or bromide, chloramine-T and 4,4′ bis (dimethylamino)diphenylmethane.

A non-suppressed ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP-MS) was developed for simultaneous determination of trace IO3- and

determination of I- in seawater without any interference. Anions such as NO3-

which absorb in the UV region do not interfere because the I-

The detection limit was *ca*. 20 pg iodide injected.

sample with 0.5 and 6 ng /ml for iodide and thiocyanate, respectively.

directly by using anion-exchange column,

, NO2-

peak is well resolved from the

, Br-

and Br- and relatively small of I-) IC and HPLC are useful

acid, was spectrophotometrically determined at two well defined UV absorption maxima of 352 and 288 nm. The results were comparable with a standard, ranging from 37.39 (±0.15) to 63.67 (±0.16) mg KIO3 per kg of salt with samples of 0.15-0.21 g.

A flow injection method based on the catalytic action of iodide on the colour-fading reaction of the FeSCN2+ complex was proposed and applied in order to determine iodine in milk. At pH 5.0, temperature 32°C and measurements at 460 nm, the decrease in absorbancy of Fe3+- SCN (0.10 and 0.0020 mol /l) in the presence of NO2 - (0.3 mol/ l) is proportional to the concentration of iodide, with a linear response up to 100.0 μg/l. The detection limit was determined as 0.99 μg/l and the system handles 48 samples per hour. Organic matter was destroyed by means of a dry procedure carried out under alkaline conditions. Alternatively, the use of a Schöninger combustion after the milk dehydration was evaluated. The residue was taken up in 0.12 mol/l KOH solubilization. For typical samples, recoveries varied from 94.5 to 105%, based on the amounts of both organic matter destroyed. The accuracy of the method was established by using a certified reference material (IAEA A-11, milk powder) and a manual method. The proposed flow injection method is now applied as an indicator of milk quality on the Brazilian market (de Araujo Nogueira et al., 1998).

Another spectrophotometric flow injection method for the determination of I- and based on the catalytic effect of this ion on the oxidation of pyrocatechol violet by potassium persulphate has been developed. The method allows the determination of 0.5–5 mg/l I at a rate of 60 samples per hour and is subject to very little interference. It was successfully applied to the determination of iodide in table salt (Cerda et al., 1993).
