요오드 분석방법 문의

이름 : AnApex | 작성일 : 2008.07.28 09:20 | 조회수 : 17857

Common inorganic iodine exists as iodide (e.g. KI), iodate(e.g.KIO3), and iodine (molecular iodine, i.e. I2). In low pH (high acidity), iodide is easily oxidized to molecular iodine (I2) by dissolved oxygen. If iodide is prepared in diluted nitric acid, the oxidation is even more significant. The memory effect is seen from molecular iodine but not from iodide or iodate. The iodide and iodate would behave like other metals in terms of memory effect. In other words, if iodate is prepared either in low pH or high pH medium, no memory effect is seen. If iodide is prepared in low pH medium (pH 2 or 3, for example), memory effect is significant, but if iodide is prepared in high pH medium (pH > 8 - 9), no memory effect. Certainly, iodine (iodide, iodate, or molecular iodine) is quite different from other metals in terms of ionization potential. In addition to the memory effect when iodide is prepared in low pH medium, the more severe problem is the different sample introduction efficiency when iodide is introduced as a "regular" solution (as iodide ion in water) and when iodide is introduced as I2 (molecular iodine in water). This is something like a hydride generation (e.g. As as As ion in water and As as AsH3 in water). In fact, methods are available that iodide is oxidized to I2 on purpose and molecular iodine (I2) is separated from solution by using a gas-liquid parator. Using ammonium hydroxide to wash between samples would help to clean the residual molecular iodine (i.e. to remove memory effect), but this would not eliminate the problem caused by the different sample introduction efficiency when iodide is prepared in low pH medium. One way to go is to adjust sample and standard to high pH. Metals are precipitated at high pH (a simultaneous analysis of iodine with other metals probably is not likely). Iodide or iodate will not be Precipitated. However, the co-precipitation of iodine (iodide and iodate) with other components needs to be confirmed. - PLASMACHEM - ----------------------------------------------------------- 요오드 분석시 시료와 표준용액을 0.1%(w/v) tetramethyl ammonium hydroxide(TMAH) base로 준비하시면 Spray Chamber에서 I2(iodine)형성을 막는것으로 알고 있습니다. 참고하시기바랍니다.
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