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  • 學位論文

海水中測定溶氧之精密光學方法及其干擾因子研究

High Precision Colorimetric Method for the Determination of Dissolved Oxygen in Seawater and Studies of Possible Interfering Factors

指導教授 : 白書禎

摘要


本研究探討溫度、碘離子濃度、氧化劑與懸浮物對於碘光度測氧法的干擾影響。碘光度法所測得的訊號來自於兩碘物種的混合光譜(如I2 和 I3-),故兩物種的平衡狀態是決定準確度的重要因素。實驗中必須利用高濃度的碘離子醃劑來確保[I_3^- ]/[I_2 ]比例的恆定。除此之外,溫度是值得注意的問題,溫度的提升會使得碘分子的吸收訊號下降,但卻會使得三碘錯離子的吸光值增加。以溶氧值約250μM的淡水樣品為例,每上升1℃會造成溶氧值高估0.40%。所以溫度改變不只影響了碘物種的平衡,同時也改變了碘物種的光譜。為了解決這一問題,研究中利用恆溫裝置改裝了分光光度計,使測量過程中的溫度變動可以維持在0.5℃內。此外,自然環境中廣泛存在著碘酸根、過氧化氫與亞硝酸根等氧化物,這些物質都會影響溶氧的測量。幸運的是利用反加試劑扣除法即可快速有效解決碘酸根的干擾;過氧化氫的干擾則可以透過添加鉬酸鹽來催化反應後才可扣除。至於亞硝酸根部分則建議添加疊氮化鈉來遮蔽其干擾。懸浮物干擾方面,因採樣過程中樣品無法過濾,容易受到懸浮物的影響,建議測完溶氧後原瓶添加硫代硫酸鈉,褪色後再次測量即可扣除水中的懸浮物干擾。綜合以上發現,碘離子試劑濃度、溫度、氧化劑與懸浮物皆會干擾碘光度測氧法的測量,唯有控制好以上干擾因素才有助於再提升溶氧測定的準確性與精密性。

關鍵字

溶氧 光度法 溫度 碘離子 氧化劑 懸浮物

並列摘要


This study investigates effects of temperature, iodide concentration, oxidants and suspended solid on the colorimetric determination of oxygen in natural waters. Since the measurement involves the mixture of two iodine species (i.e. I2 and I3-), the equilibrium between them becomes a crucial factor to the precision of the method. A high concentration of iodide in the pickling reagent was found essential to ensure a stable [I_3^- ]/[I_2 ] ratio. Besides, it was also found that elevated temperature can cause a lower signal of molecular iodine, but increase the absorbance of triiodide ion. An over-all increment of 0.4% per 1 ℃ has been observed for a freshwater sample having oxygen concentration of ca. 250 μM. Therefore, temperature deviation can not only change the equilibrium constant but also alter the spectra of both iodine species. To solve this problem, the spectrophotometer has been modified using a thermostat unit which ensures the temperature difference between samples be kept within 0.5 ℃. Iodate, hydrogen peroxide, nitrite which are known to exist in natural environment all interfere the oxygen measurement. A quick reverse pickling procedure can be used to identify the iodate interference. Addition of sodium azide is always suggested to remove overestimate from nitrite. Since the sampling for oxygen usually excludes filtration therefore suspended solid in a sample can be another source of error. Re-measurement of the absorbance of the same sample after adding sodium thiosulfate reagent to remove the iodine color is considered the most effective way to correct for the interference from turbid water.

並列關鍵字

oxygen colorimetry temperature iodide oxidants suspended solid

參考文獻


[17] 黃冠綸, (2006) 碘光度測氧法干擾因子之研究. 國立台灣大學海洋研究所碩士論文,共62頁。
[33] 鄭家侖, (2007) 以兩種光度法測試酸礦水溶氧的可行性研究. 國立台灣大學海洋研究所碩士論文,共74頁。
[22] 白書禎、郭廷瑜、鐘仕偉、蘇宗德,(1998) 疊氮修正希巴辣光度測氧法及其在環境監測上的應用。 化學(中國化學會誌), 56(3),173-185
[35] 郭子彥, (2003) 懸浮顆粒濃度在淡水河口之時空變化. 國立臺灣師範大學地球科學系碩士論文,共69頁。
[1] Greeberg, A. E., Clesceri, L. S., Eaton, A. D. (1992) Standard Methods for the Examination of Water and Wastewater, 18th ed. American Public Health Association, Washington D.C.

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