摘要:

Iodide is essential for the synthesis of thyroxine, which is responsible for growth and development in humans. Goitre and cretinism are two major clinical manifestations of iodide deficiency;1other inadequacy effects being abortions, still births, congenital abnormalities, increased perinatal and infant mortality, psychomotor defects and impaired mental function. Out of 239 districts surveyed in India, 197 were found to be endemic for goitre. About 150 million of the Indian population is at risk of iodide deficiency, 55 million for goitre, 2.2 million for cretinism and 6.6 million for milder neurological defects.2Marketing iodized table salt, which is the most frequent way of obtaining an additional supply of iodide, is mandatory in India.The daily adult requirement is 100–300 μg of iodide. An intake consistently below 50 μg d−1results in endemic goitre whereas excess iodide can produce both hypo- and hyperthyroidism.3Therefore, iodide level in food, drugs and water can have profound effects on the thyroid status of individuals. The use of iodine as a disinfectant for drinking water is well established. Strongly basic quaternary ammonium anion-exchange resins behave as demand-type disinfectants against a wide variety of bacteria and viruses. Resin-treated drinking water has been found to contain 20–4200 μg l−1iodide.4For long-term use of these halogenated resins, appropriate post-treatment measures must be taken to adjust the halogen to an acceptable level.Iodine is a trace element in sea-water.5It exists mainly as iodate and lower concentrations as iodide; the total inorganic iodine is approximately in the range 50–60 μg l−1whereas iodide is in the range 1–30 μg l−1.6The distribution of iodide and iodate gives clues to understanding the marine environment. Total iodine has been determined by oxidizing iodide to iodate and determining the latter by differential pulse polarography6or spectrophotometrically after conversion to triiodide;7the triiodide was also found to oxidize leuco Crystal Violet to the Crystal Violet dye, which was then determined.8However, as the limit of detection for iodide determined by difference of two separate methods is not good, it is desirable to detect iodide directly.A few methods are available for the direct determination of iodide,9but some of the electrochemical10–12or neutron activation analysis13methods are cumbersome and time consuming. Ion chromatography has been used for the direct determination of iodide.6,9,14High levels of chloride in the medium affect the efficiency of chromatography but this has been avoided by adding chloride to the eluent. A limitation to routine use of this technique is the inadequate sensitivity of detection such as by conductivity, amperometry or potentiometry.5Formation of a derivative of iodide that is more detectable is one way to overcome this difficulty. Derivatization of iodide to 2-iodoethanol by reaction with ethylene oxide15or to iodoacetone by oxidation in the presence of acetone16followed by GC using electron capture detection have been used. Still another route is derivatization to 4-iodo-2,6-dimethylphenol followed by either reversed-phase HPLC with UV detection17,18or GC-MS.4Although the limit of detection of these methods is still not sufficient (Table 1), it could be improved by a preconcentration step.19The only remaining deficiency would be the 20–30 min reaction time to form the derivative. A new method is proposed in this paper which is based on derivatization of iodide to 4-iodo-N,N-dimethylaniline, a reaction that goes to completion within 1 min, followed by sensitive determination by GC-MS.Comparison of sensitivity of chromatographic methods for iodide determinationColumnDetectionLODl−1Ref.SBAWS = series bulk acoustic wave sensor; ECD = electron capture detection; MSD = mass-selective detection.LOD = limit of detection.Ion chromatography—Vydac 302 ICSpectrophotometry1 μg20HIKS-1Conductivity10 mg21Weakly basic anion exchangerPotentiometry15 mg22IC-Pak anionAmperometry0.7 mg23Wescan anionPotentiometry100 mg24Dionex HPIC-AS1Amperometry10 μg25TSK gel SAXUV200 ng 9HPIC AS-11Conductivity0.3 mg26AS4A-SC anion exchangeConductivity0.1 mg27AS4A-SC anion exchangeUV1 μg27Shimpack IC-A1SBAWS conductivity5 μg28C18coated with cetylpyridinium chloridePotentiometry1.47 μg29Liquid chromatography—C18UV5 μg17(derivatization to 4-iodo-2,6-dimethylphenol)Gas chromatography—Neopentylglycol sebacate on Chromosorb G HPECD114 ng16(derivatization to iodoacetone)CarbowaxECD8 μg15(derivatization to 2-iodoethanol)HP-5MSMSD500 ng 4(derivatization to 4-iodo-2,6-dimethylphenol)HP-5MSD8 ngThis work(derivatization to 4-iodo-N,N-dimethylaniline)

ISSN:0003-2654    

出版商:RSC    

年代:1999

数据来源: RSC