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Determination of Iodide and Iodate in Aqueous Solution

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Determination of Iodide and Iodate in Aqueous Solution DETERMINATION OF IODIDE AND IODATE IN AQUEOUS SOLUTION by YINING LIU, B.Sc. A THESIS IN CHEMISTRY Submitted to the Graduate Faculty of Texas Tec University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved Purnendu K. Dasgupta Chairperson of the Committee Dimitri Pappas Co-Chair of the Committee Carol Korzeniewski Member of the Committee Accepted John Borrelli Dean of the Graduate School August, 2007 Copyright 2007, Yining Liu Texas Tech University, Yining Liu, August, 2007 ACKNOWLEDGEMENTS I would like to express my deepest appreciation to Dr. Purnendu K. Dasgupta, my dear mentor and advisor. Without his continuous guidance and encouragement, my achievements towards a Master’s degree in Chemistry would not have been possible. I would like also thank Dr. Dimitri Pappas and Dr. Carol Korzeniewski for their assistance and valued comments on my thesis work. I would like to express my great appreciation to those people in our group, especially to Dr. Kalyani Martinelango, Dr. Qingyang Li, Dr. Takeuchi Masaki and Mr. Jason V. Dyke. Those people gave me a lot of advice and guidance to assist me to finish my research projects. Last but not least, I would like to thank my family for their continuous support and understanding of my studying thousands miles away from home. I love you all. Finally, my deepest love would be expressed to my wife, Xia Wei, thank you to be always along with me, patient and supportive. It’s my pleasure to enjoy the great journey of life with you. ii Texas Tech University, Yining Liu, August, 2007 TABLE OF CONTENTS ACKNOWLEDGEMENTS...…………………………………..….………...……...…… ii ABSTRACT………………………………………………………………….…….….. viii LIST OF TABLES…………………………………..………...….………...……............. x LIST OF FIGURES…………………………………….....……..…..……………….… .xi LIST OF ABBREVIATIONS...………………………..…………….……….…..…. …xiv CHAPTER I. INTRODUCTION: IODINE...………….……..............................……………….. 1 1.1 Historical Discovery…………………………………….................……… 1 1.2 Physical and Chemical Properties………..……………………...............1 1.3 Occurrence, Production and Uses....................................................... 2 1.4 Health Importance of Iodine…………………………………….…………3 1.4.1 Goiter.......................................................................................... 3 1.4.2 Neurological Disorder................................................................. 4 1.4.3 Hazard and Toxicity……............................................................. 4 1.5 Prevention of IDD Worldwide…............................................................ 4 1.5.1 Iodized Intake Regulation……………………..………….………...5 1.5.2 Iodized Salt in United States………………………………………..7 iii Texas Tech University, Yining Liu, August, 2007 1.6 Objectives of Present Work…………….................................................7 1.7 References............................................................................................9 II. SOURCE OF DIETARY IODINE SUPPLEMENT: IODIZED TABLE SALT PROGRAM IN THE UNITED STATES..................................................…….11 2.1 Introduction....................................................................................... 11 2.2 Analytical Methods for the Determination of Iodide………….……..…11 2.2.1 EPA Standard Method…………..…………………….……......... 11 2.2.2 Other Reported Methods……................................................... 12 2.3 Experimental Section….................................................................... 14 2.3.1 ICP-MS Condition…………...................................................... 14 2.3.2 Chemicals and Reagents......................................................... 14 2.3.2.1 Internal Standard…………………………………..………...14 2.3.2.2 Reference Standards and Sample Preparation…………..15 2.3.3 Measurements…………………………………........................... 16 2.4 Results and Discussion………………………………..…………...……17 2.4.1 Stability of Iodine in Table Salt.................................................. 17 2.4.1.1 Effect of Humidity..…........................................................ 17 2.4.1.2 Effect of Temperature....................................................... 18 2.4.1.3 Effect of Light................................................................... 18 2.4.2 Study of Iodized Salts Sold in US Market................................. 19 iv Texas Tech University, Yining Liu, August, 2007 2.4.2.1 Iodized Salt in US……..................................................... 19 2.4.2.2 Inhomogeneity of Iodine in Iodized Salt........................... 20 2.4.2.3 Study of Iodized Salt by States......................................... 20 2.4.2.4 Study of Iodized Salt by Brand…………….………..…..…21 2.4.2.5 Does Iodine Content Decay Over a Period of Time Under Actual Use Conditions?....................................................21 2.5 Conclusion……………..….............................................................. 23 2.6 References....................................................................................... 24 III. AN AMPEROMETRIC IODATE ANALYZER FOR AQUEOUS SAMPLES....38 3.1 Introduction....................................................................................... 38 3.2 Experimental Section……………………………….…….…….….……38 3.2.1 Instrument Setup…………………………….............................. 38 3.2.1.1. Amperometric Detector Cell………………….………...….38 3.2.1.2 NAFION Tube & Acid Penetration …..………………….…39 3.2.1.3 Data Acquisition………………………………..…...……….42 3.3 Result and Discussion part I: Determination of Iodate in Chilean Caliche Soil.................................43 3.3.1 Standard Detection Method...................................................... 43 3.3.2 SCIC on Determining Iodate in Caliche Samples......................43 v Texas Tech University, Yining Liu, August, 2007 3.3.3 Improved Iodate Amperometric Detection.................................44 3.3.4 Detector Interface to the Ion Chromatography System………..44 3.3.5 Preparation of Samples and Reagents......................................45 3.3.5.1 Sample Preparation..........................................................45 3.3.5.2 Chemicals and Reagents..................................................45 3.3.6 Optimization of Detection System.............................................45 3.3.6.1 Optimization of Applied Voltage........................................45 3.3.6.2 Gradient Eluent Protocol...................................................46 3.3.7 System Response.................................................................... 46 3.3.7.1 Calibration and Determination of Iodate………………..…46 3.3.7.2 Selective Detection of Iodate over Fluoride......................47 3.3.7.3 Iodate in the Chilean Caliche Samples…..…………….….47 3.4. Result and Discussion part II: Determination of Iodate in Table Salt................................................49 3.4.1 Analytical Methods of Iodate Determination………...…………..49 3.4.1.1 Standard Methods…………………………...……………....49 3.4.1.2 Spectrometric and Electrochemical Methods………….….49 3.4.1.3 Sensitive Amperometric Detection of Iodate in Table Salt Solution…...……………………………....………....…51 3.4.2 Preparation of Samples and Reagents……...……………….….51 vi Texas Tech University, Yining Liu, August, 2007 3.4.2.1 Sample Preparation……………………………...………….51 3.4.2.2 Chemicals and Reagents…………………….……………..52 3.4.3 Flow Injection Analysis System…………………....……………..52 3.4.4 Optimization of Detection System…………..………………..…..53 3.4.4.1 Optimization of Applied Voltage………………...…...……..53 3.4.4.2 Optimization of Flow Injection Variables………..…….......53 3.4.5 System Response……………………………..………….……….54 3.4.5.1 Calibration and Determination of Iodate in Iodized Salts…………………………………………………………..54 3.4.6 Real Sample Result and Discussion………….………...……….54 3.5 Conclusion………………………..…………………………...………….55 3.6 References………………………………..………………………………56 IV. CONCLUSIONS...........................................................................................73 vii Texas Tech University, Yining Liu, August, 2007 ABSTRACT Sufficient daily dietary iodine (I2) intake is necessary for the production of thyroid hormones. Insufficient iodine intake or assimilation impairs the synthesis of thyroid hormones and may result in hypothyroidism. If hypothyroidism occurs early in life, a range of functional and physiological abnormalities collectively termed “Iodine Deficiency Disorders” (IDD) may develop. Iodate and Iodide are the only two forms in which iodine is added to table salt. Iodide is used in the US but iodization has never been mandatory and iodine content of table salt has never been determined independently. Potassium iodide (KI) added to table salt may oxidize and then sublime at ambient humidity and temperature. Further additives are sometimes added to salt, including silica or calcium silicate (to maintain free flowing characteristics) and dextrose or sodium thiosulfate (as an iodine preservative). We have collected table salt supplied by volunteers from across the US. The iodine content of the salt samples was measured by ICP-MS with Ge as an internal standard. The determination of iodate is of great interest for the studies of an iodized salt program in Asian countries because iodate is the iodization vector for salt in Asia. Iodate is also naturally formed and the content of iodate in natural deposits is of interest. We describe an electrochemical detection system in which viii Texas Tech University, Yining Liu, August, 2007 aqueous iodate is reduced on a stainless steel working electrode with a platinum auxiliary electrode in acidic
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