**4.2.3 Food**

GC method has been developed for determination of total iodine in food, based on the reaction of iodine with 3-pentanone. Organic matter of a sample was destroyed by an alkaline ashing technique. Iodide in a water extract of the ash residues was oxidized in order to free I2 by adding Cr2O72- in the presence of H2SO4. Liberated iodine reacted with 3 pentanone to form 2-iodo-3-pentanone, extracted into n-hexane, and then determined by gas chromatography with an electron-capture detector. Recoveries of I- from spiked food samples ranged from 91.4 to 99.6%. Detection limit for iodine was 0.05 μg/g (Mitsuhashi & Kaneda Y, 1990).

Two methods were described for the preparation of samples for total iodine measurement in milk and oyster tissue. In the first method, the samples were combusted in a stream of oxygen to release iodine that, subsequently, was trapped in a solution as iodide. The second method used a new approach in which the samples were oxidized in a basic solution of peroxydisulfate. In this case, iodine was retained in the solution as an iodate. Total iodine

iodide in seawater. An anion-exchange column (G3154A/101, Agilent) was used for the

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

determine IO3- and I- in seawaters without sample pre-treatment (with exception of dilution)

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

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

A gas chromatography (GC) method was reported for the trace analysis of I- in processed seaweed by Lin et al. (Lin et al., 2003). The method is based on the derivatization of aqueous iodide extracted from seaweed with 2-(pentafluorophenoxy)ethyl 2 (piperidino) ethanesulfonate in toluene using tetra-*n*-hexylammonium bromide as a phase-transfer

GC method has been developed for determination of total iodine in food, based on the reaction of iodine with 3-pentanone. Organic matter of a sample was destroyed by an alkaline ashing technique. Iodide in a water extract of the ash residues was oxidized in order to free I2 by adding Cr2O72- in the presence of H2SO4. Liberated iodine reacted with 3 pentanone to form 2-iodo-3-pentanone, extracted into n-hexane, and then determined by gas chromatography with an electron-capture detector. Recoveries of I- from spiked food samples ranged from 91.4 to 99.6%. Detection limit for iodine was 0.05 μg/g (Mitsuhashi &

Two methods were described for the preparation of samples for total iodine measurement in milk and oyster tissue. In the first method, the samples were combusted in a stream of oxygen to release iodine that, subsequently, was trapped in a solution as iodide. The second method used a new approach in which the samples were oxidized in a basic solution of peroxydisulfate. In this case, iodine was retained in the solution as an iodate. Total iodine

ion chromatography approach utilizing UV detection (Bruggink et al., 2007).

with an eluent containing 20 mM NH4NO3 at pH 5.6. NH4NO3 used


separation of IO3- and I-

(Chen et al., 2007).

**4.2.2 Seaweed** 

catalyst.

**4.2.3 Food** 

Kaneda Y, 1990).

river were 0.18-8.34 μg/l.

detection limit was 1.5 μg/L for IO3

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

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

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

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

A Review of Spectrophotometric and Chromatographic Methods

developed IC method was supported by validation results.

**5. Conclusion** 

methods.

**6. Acknowledgment** 

**7. References** 

spectrophotometric determination of I-

levels for iodide as: 1.7–170, 8.1μg/l (Blount & Valentin-Blasini, 2006).

and Sample Preparation Procedures for Determination of Iodine in Miscellaneous Matrices 389

measured iodine concentrations (3.52 ± 0.29 ppm; V.C. = 10 %) was achieved. Suitability of the

Ion chromatography coupled with electrospray ionization tandem mass spectrometry was applied for quantifying iodide, as well as perchlorate and other sodium-iodide symporter (NIS) inhibitors in the human amniotic fluid*.* The use of selective chromatography and tandem mass spectrometry decreased the need to clean up samples, leading to a quick and rugged method that is capable of the routine analysis of 75 samples per day. Along the physiologically relevant concentration range for the analytes, the analytical response was linear. The analysis of a set of 48 samples of amniotic fluid identified the range and median

There are many analytical methods available for detecting, and/or measuring iodine and its various species in complex matrices. Unfortunately, there is no perfect method which would be accurate, sensitive, cheap, fast, simple, and free of interferences at the same time. This review has been focused mainly on applications of spectophotometric and chromatographic methods of iodine analysis because they are widely used in practice, and relatively cheap. What is more, to achieve lower detection limits, they can also be coupled with other more sophisticated techniques (eg. ICP-MS). Although, these two methods have their own limitations, connected mainly with sample preatretment step (often timeconsuming), the literature data show continuous progress in the search for the best spectrophotometric and chromatographic conditions in iodine determinations. Reduction of time necessary for sample preparation still remains a challenge for analysts. Summarizing, future directions of iodine analysis lie rather in the simplification of methodologies and their extensive accessibility rather than in the tendency to decrease the limit of detection. Some recently published papers on the determination of iodine include: the evaluation of urinary iodide by the use of micro-photometric method compared to ICP-MS results (Grimm et al., 2011); determination of iodine and its species in plant samples using IC-ICP/MS (Lin et al., 2011);

> , IO3 - , IO4 -

and sea water (George et al., 2011); investigation of the concentration-dependent mobility, retardation, and speciation of iodine in surface sediment from the river (Zhang et al., 2011); comparison of Sandell-Kolthoff reaction with potentiometric measurements of urinary iodide in female thyroid patients (Kandhro et al., 2011). One of the newest studies concerns the analysis of food samples by ICP-MS after alkaline digestion with TMAH (Tinggi et al., 2012). As it turns out, the newest published works utilize the most common already existing

My appreciation and thanks are given to Prof. Ryszard Maciejewski, Vice Rector for

Adams, J.B., Holloway, C.E., George, F. & Quig, D. (2006). Analyses Of Toxic Metals And

Essential Minerals In The Hair Of Arizona Children With Autism And Associated

Research at the Medical University of Lublin, for financial support of the research.

in table salt, pharmaceutical preparations

only 15-50% of the total iodine was found in the milk whey. Adding sodium dodecyl sulfonate (SDS) improved considerably the recovery of iodine from these samples (in case of the natural milk samples, this increase was ca. 10±20% but for infant formula samples the amount of iodine recovered in the supernatant was more than twice that in the samples not incubated with SDS). Iodine was found to be principally present as iodide in all the samples except infant formulas. In the latter, more than half of iodine was bound to a high molecular (>1000 kDa) species. The sum of all the species recovered from a size-exclusion column accounted for more than 95% of the iodine present in a milk sample. For the determination of total iodine in milk, a rapid method based on microwave-assisted digestion of milk with ammonia followed by ICP MS was optimized and validated using CRM 151 Skim Milk Powder (Fernandez-Sanchez & Szpunar, 1999).
