Molecular iodine selective membrane for iodate determination in salt samples: chemical amplification and preconcentration

Abstract

A molecular iodine selective membrane has been used for preconcentration of I(2) generated in situ by iodometric reaction of IO(3)(-) with excess I(-) in acidic medium (pH 1-2). This iodometric reaction amplifies the iodine content six times resulting in enhancement of analytical response ranging from three times for molecular methods to six times for elemental methods. The chemical conditions of this iodometric reaction were optimized for quantitative generation and subsequent sorption of I(2) in the membrane samples (96 +/- 3%). The homogeneous transparent membrane was prepared by immobilizing I(2)-complexing polyvinylpyrrolidone (PVP) in the plasticized cellulose triacetate matrix. Four different analytical methods were examined for quantitative determination of IO(3)(-) in iodized salt samples by preconcentrating it as I(2) in the membrane matrix. These methods were: (1) spectrophotometry of the PVP-I(2) complex formed in the membrane matrix, (2) a radiotracer method using I(-) tagged with (131)I radiotracer, (3) instrumental neutron activation analysis (INAA), and (4) energy-dispersive X-ray fluorescence (EDXRF) analysis. The IO(3)(-) contents thus determined in the iodized salt samples by the membrane-based radiotracer method were compared with the total iodine determined in salt samples by epithermal instrumental neutron activation analysis (EINAA). The membrane-based method for iodate determination in salt samples has advantages over conventional analytical methods, for example preconcentration and chemical amplification, and is free from interference from anions.

A Simple and Rapid Spectrophotometric method for the determination of Iodate in table salt samples using Pyrogallol red dye

“…However, in India iodate is preferentially added over iodide for iodization of salt. The presence of iodate in some locally available table salt samples has been determined and reported in our previous work 19 . The effect of Ion the oxidation of pyrogallol red by iodate was studied and the studies indicated that the presence of iodide upto 1 g did not interfere in the iodate determination.…”

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

“…The amount of potassium iodide and the concentration of acid were optimized in a similar manner as reported in our previous work (Bhagat et al 2008) The concentration of iodate was fixed as 10 μg during the optimization experiments. Experiments were performed to optimize the dye concentration and pH of the reaction mixture.…”

“…The amount of iodide was varied between 250 and 1,000 μg. It was found that 250 μg of I − was enough to convert IO 3 − to I 2 quantitatively (Bhagat et al 2008). The pH of the reaction mixture was varied between 2.5 and 11.…”

“…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 chromatography-mass 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).…”

An optical sensor for selenite determination in aqueous samples

“…With this background in the present work, we have employed the same iodometric reaction for generation of iodine with a cellulose triacetate membrane plasticized with di-octyl phthalate containing Al-336 anion exchanger as the solid phase medium. The solid phase medium is employed as an optical sensor for Se (IV) determination using iodometric reaction The chemical conditions required for the iodometric reaction between SeO 3 2− and I − in presence of acid were optimized in our earlier work using 131 I radiotracer and it indicated that the iodine sorption in the membrane is quantitative, reproducible, and without any losses (Bhagat et al, 2008). Cellulose tri-acetate is a highly crystalline, hydrophobic base polymer, that enhances mechanical strength and provides stability to the membrane.…”