**4.2.1 Water samples**

384 Macro to Nano Spectroscopy

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

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

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

Due to the noninvasive way of sampling, urine is the most commonly analysed biological fluid. Efficient management of national salt iodization programmes depends on quality data on iodine concentrations in the urine and salt samples. These data are crucial in the evaluation of iodine interventions. Most of the analytical methods for urinary iodine concentration are based on the manual spectrophotometric measurement of Sandell-Kolthoff reduction reaction catalyzed by iodine using different oxidising reagents in the initial digestion step (Jooste & Strydom, 2010). Bilek et al. (Bilek et al., 2005) used a method which was based on alkaline ashing of urine specimens preceding the Sandell-Kolthoff reaction using brucine as a colorimetric marker. The detection limit was 2.6 µg/l and the limit of quantification was 11.7

Another study described simple photometric determination of the iodine concentration in the thyroid tissue of small animals. Again, the method was based on the well-known catalytic Sandell-Kolthoff reaction. Prior to the analysis, the tissue was digested in a mixture of sodium chlorate and perchloric acid at 100 degrees C. Using this manner of digestion between 94 and 110% of iodine in the sample was recovered. Comparison with the neutron activation analysis showed excellent agreement of the obtained values (Tiran et al., 1991).

While the main advantage of catalytic spectrophotometric methods is low cost of the needed equipment, chromatography is arguably the most widely used separation technique in the

63.67 (±0.16) mg KIO3 per kg of salt with samples of 0.15-0.21 g.

of milk quality on the Brazilian market (de Araujo Nogueira et al., 1998).

applied to the determination of iodide in table salt (Cerda et al., 1993).

µg/l, with intra-assay precision of 4% and inter-assay precision of 4.9%.

**4.1.4 Biological fluids and tissues** 

**4.2 Chromatographic methods** 

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 determination of I- in seawater without any interference. Anions such as NO3-, NO2 -, Brwhich absorb in the UV region do not interfere because the I peak is well resolved from 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 sample with 0.5 and 6 ng /ml for iodide and thiocyanate, respectively.

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

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

A Review of Spectrophotometric and Chromatographic Methods

91 and 103% (Gu et al., 1997).

10 µg/g) (International Standard ISO, 2009).

and Sample Preparation Procedures for Determination of Iodine in Miscellaneous Matrices 387

was measured by means of the GC analysis of the 2-iodopentan-3-one derivative. The methods were tested using Standard Reference Materials (SRMs) 1549 Non-Fat Milk Powder, and 1566a and 1566 Oyster Tissue. Also, KI and KIO3 were used for testing the procedures. The results obtained for the SRMs, given as average +/- standard deviation in μg/l, were: 3.39 +/- 0.14 and 3.40 +/- 0.23 for SRM 1549; 4.60 +/- 0.42 and 4.51 +/- 0.45 for SRM 1566a; and 2.84 +/- 0.16 and 2.76 +/- 0.06 for SRM 1566; values corresponding to combustion and wet oxidation, respectively. Overall, the absolute recoveries varied between

Cataldi and Ciriello (Cataldi & Ciriello, 2005) described a sensitive method based on anionexchange chromatographic separation coupled with amperometric detection at a modified platinum electrode under constant applied potential (+0.85 V vs. Ag AgCl). An experimental setup with an in-line and very effective method of electrode modification was proposed using an amperometric thin-layer cross-flow detector and a flowing 300 mg/l solution of iodide. The working electrode was polarized to the limiting current for oxidation of iodide to iodine in acidic solutions with the consequent formation of an iodine-based film. The results confirmed that the modified electrode exhibits high analytical response for iodide electro-oxidation with a good stability and long-life. The detection limit of iodide was estimated to be 0.5 µg/l (S/N=3) with an injection volume of 50 μL. This method was applied successfully to quantify the iodide content of milk samples, wastewaters, common vegetables and solutions containing high chloride levels. The iodide peak was always observed without interferences from the excess of coexisting anions (e.g. Cl-, SO4 2- or Br-). Chloride (the main component of marine samples) exhibited no effect upon the separation and detection of iodide. The same method (RP ion pair HPLC with an electrochemical detector and a silver working electrode) was considered by the International Organization for Standardization (the determination of iodide content of pasteurized whole milk and dried skimmed milk when present at levels from 0.03 µg/g to 1 µg/g and from 0.3 µg/g to

Xu et al. (Xu et al., 2004) described a method for determination of iodate developed by RP-HPLC with UV detection. Iodate was converted to iodine, which was separated from the matrix using a reversed-phase Ultrasphere C18 column (250×4.6 mm, 5 µm) with methanol (1M) H3PO4 (1:4) as the mobile phase at 1.00 ml/min and UV detection at 224 nm. The calibration graph was linear from 0.05 µg/ml to 5.00 µg/ml for iodine with a correlation coefficient of 0.9994 (*n*=7). The detection limit was 0.01 µg/ml. The recovery was from 96%

A method based on the coupling of size-exclusion chromatography (SEC) with on-line selective detection of iodine by ICP MS was developed allowing determination of iodine species in milk and infant formulas. Iodine species were quantitatively eluted with 30 mM Tris buffer which was prepared by dissolving 30 mM of tris [tris(hydroxymethyl) aminomethane] in water and adjusting the pH to 7.0 by the addition of hydrochloric acid (1 : 10, v/v) within 40 min and detected by ICP MS with a detection limit of 1 μg l-1 (as I). A systematic study of iodine speciation in milk samples of different animals (cow, goat) and humans, of different geographic origin (several European countries) and in infant formulas from different manufacturers was carried out. When obtained after centrifugation of fresh milk or reconstituted , milk powders contained more than 95% of the iodine initially present in the milk of all the investigated samples with the exception of the infant formulas in which

to 101% and the relative standard deviation was in the range of 1.5% to 2.9%.

iodide in seawater. An anion-exchange column (G3154A/101, Agilent) was used for the separation of IO3- and I with an eluent containing 20 mM NH4NO3 at pH 5.6. NH4NO3 used in mobile phase minimizes salt deposition on the sampler and skimmer cones of mass spectrometer. Linear plots were obtained in a concentration range of 5.0–500 μg/l and the detection limit was 1.5 μg/L for IO3 - and 2.0 μg/l for I-. The proposed method was used to determine IO3- and I- in seawaters without sample pre-treatment (with exception of dilution) (Chen et al., 2007).

Using IC-ICP-MS, Tagami and Uchida (Tagami & Uchida, 2006) measured concentrations of halogens (Cl, Br and I) in 30 Japanese rivers. Cesium was used as an internal standard during I counting. The typical detection limit was calculated as three times the standard deviation of the blank, between 0.01–0.04 μg/l. The ranges of geometric means of I in each river were 0.18-8.34 μg/l.

Bruggink et al. developed an anion-exchange chromatography method in combination with the pulsed amperometric detection (PAD) for the analysis of dissolved I- in surface water and in absorption solutions obtained from adsorbable organic iodide (AOI) determination. The development of the amperometric waveform for a selective detection using a silverworking electrode together with the optimization of the injection volume and digital signal smoothing was performed. This method exhibited a detection limit of 0.02 μg/L, without any need of sample treatment other than micro-filtration. The results of AOI determination of the method described in this article were compared with results obtained with a different ion chromatography approach utilizing UV detection (Bruggink et al., 2007).
