A rapid assessment method for determination of iodate in table salt samples

Preeti S Kulkarni 0 Satish D Dhar 2 Sunil D Kulkarni 1 0 Department of Chemistry, Postgraduate and Research Centre, MES Abasaheb Garware College , Pune-411005, India 1 Department of Chemistry , Sir Parashurambhau, Pune-411030, India 2 Modern College , Shivajinagar, Pune 411005, India Background: In the present work, a simple and rapid method for determination of iodate is described. Methods: Iodometric reaction between iodate, excess iodide, and acid has been used, and the iodine liberated is allowed to react with variamine blue (VB) dye in the presence of sodium acetate to yield a violet-colored species. Results: A calibration curve was obtained in the concentration range of 2 to 30 g of iodate in a final equilibration volume of 10 mL. The effect of different interfering anions on determination of iodate was also studied. Conclusions: The developed method was applied to iodate determination in various iodized salt samples obtained from local markets in and around Pune city, India. The amount of iodate in various table salt samples was in the range of 10 to 25 ppm. - Background Iodine is an essential trace element for human nutrition. The safe dietary intake of iodine as recommended by the World Health Organization (WHO) is 100 g day1 for infants and 150 g day1 for adults (Hetzel 1983). Iodine is required by the thyroid gland for the synthesis of T3 and T4 hormones (Visser 2006). The storehouse of iodine in the human body is the thyroid gland. Inadequate intake of iodine leads to iodine deficiency symptoms and disorders like goiter, extreme fatigue, mental retardation, and depression which are collectively called as iodine deficiency disorders (IDDs). In India, about 71 million people suffer from iodine deficiency disorders. Statistics furnished by the Ministry of Health and Family Welfare in its report revealed that Uttar Pradesh, Bihar, Madhya Pradesh, Maharashtra, and Gujarat states contributing to almost 70% population have maximum IDD cases. The natural dietary sources of iodine include milk, vegetables, fruits, cereals, eggs, meat, spinach, and sea foods (Zimmermann 2009). However, natural sources of iodine may not satisfy its requirement by the body as iodine from these sources may not be in bioavailable form and also the concentration of iodine may be less. Adequate intake of iodine can be achieved by consumption of iodized salt. Iodization of salt is done by addition of iodate to salt samples due to its good stability and bioavailability (Brgi et al. 2001). Thus, determination of iodate in salt samples is of considerable importance as the amount of iodate in the salt samples may vary with environmental conditions, the nature of transport, packing conditions, and cooking methods (Bruchertseifer et al. 2003). There are various analytical methods for determination of iodate in seawater and iodized salt samples. Some of the recent methods include kinetic spectrophotometric methods (Ni and Wang 2007), flow injection analysis (Shabani et al. 2011), microspectrophotometry after liquidphase microextraction (Pereira et al. 2010), using cadmium sulfide quantum dots as fluorescence probes (Tang et al. 2010), liquid-liquid microextraction by high-performance liquid chromatography-diode array detection (Gupta et al. 2011), ion chromatography with integrated amperometric detection (Babulal et al. 2010), transient isotachophoresiscapillary zone electrophoresis (Wang et al. 2009), gas chromatographymass spectrometry (Das et al. 2004), using polymer membrane selective for molecular iodine (Bhagat et al. 2008), and neutron activation analysis method (Bhagat et al. 2009). A non-suppressed ion chromatography with inductively coupled mass spectrometry (ICP-MS) has been developed for the simultaneous determination of iodate and iodide in seawater (Zul et al. 2007). Most of the techniques are complex and involve sophisticated instruments and complex procedures. It is also observed that application of these analytical methods for iodate determination in table salt is complicated due to the presence of huge excess of chloride, for example, in the case of anion exchange chromatography with conductometric detection which requires the removal of large excess of chloride from the sample matrix (Kumar et al. 2001). Hence, development of a method that is selective for iodate and sensitive and requires simple and inexpensive experimental setup is of considerable scientific interest. Also, accurate determination of the contribution of iodine from table salt to total dietary intake requires novel methods. With this objective in the present work, a simple and rapid method for determination of iodate is described. Iodometric reaction between iodate, excess iodide, and acid has been used, and the liberated iodine is allowed to react with variamine blue (VB) dye to yield a violet-colored species with absorbance maxima at 550 nm. The developed method was applied to determine the iodate concentration in table salt samples obtained from local markets in and around Pune city in India. The kinetics of the method is very fast, and a large number of table salt samples can be screened for their iodate content in a short time. The iodate content thus determined by the developed method was compared with the iodate content determined by conventional iodometric titration. The method developed in the present work has advantages over conventional methods, for example, it is free from losses of iodine and it is interference free. Methods Apparatus A computer-based spectrophotometer (Systronics, Ahmedabad, India) was used for all the absorbance measurements. A pH meter (Labtronics, Panchkula, India) was used to monitor the pH of the equilibrating solutions. The pH meter was standardized using pH 4, 7, and 10 buffer solutions. A digital balance (Contech, Mumbai, India) was used for weighing all the reagents. Doubledistilled water was used throughout all the work which was prepared using Equitron's instrument (Mumbai, India). Reagents and solutions All reagents used were of analytical reagent grade (A.R. grade) and used without further purification. Variamine blue (Merck, Mumbai, India), potassium iodate (S.M Chemicals, Mumbai, India), potassium iodide (Loba Chemie, Mumbai, India), sodium chloride (Qualigens, Mumbai, India), potassium bromate (Qualigens), ammonium oxalate (Qualigens), potassium chloride (Qualigens), sodium bicarbonate (Qualigens), potassium nitrate (Qualigens), zinc sulfate (Qualigens), methyl alcohol (Qualigens), and magnesium carbonate (Qualigens) were used. A variamine blue dye solution was prepared by dissolving 20 mg of the dye in methyl alcohol and diluting the solution to 50 mL using distilled water. A potassium iodate solution was prepared by dissolving 0.0122 g of KIO3 in distilled water and diluting it to 100 mL [1 mL = 100 g IO3]. Sulfuric acid (1 M) was prepared by diluting 6.95 mL of stock H2SO4 to the mark in a 250-mL volumetric flask with distilled water. A solution of pota (...truncated)