河口位於河海交接處，不僅有河川持續的輸出，也有來自海洋的浪與潮在此 激烈地進行混合作用，再加上人為活動造成影響，因而形成特殊的河口環境。本 研究以鎘銅還原法測定河口廣鹽性樣本的準確性為主軸，模擬測定感潮帶水樣中 的硝酸鹽，當以濃度2%的氯化銨溶液做緩衝試劑時，同濃度的硝酸鹽標準品其吸 光值會隨著鹽度增加而減少；在整理多組的實驗數據後，發現鎘銅管還原率隨鹽 度變化的趨勢其再現性不佳，無法以一條經驗方程式解決鹽度干擾的問題，而是 需要每次測定一批樣本後，以多鹽度的標準品求得當次的修正公式，方法複雜且 耗時。因此，將目標轉為利用緩衝錯合試劑來減緩鹽度的影響，實驗發現試劑的 成分與酸鹼值皆會改變鹽度與吸光值的關係，經由交叉測試得到本文建議的緩衝 錯合試劑，其成分為濃度4% w/v 的氯化銨與 2% w/v 的乙二胺四乙酸混合溶液，
並以氫氧化鈉將試劑酸鹼值調整至7.5。
若將原本使用的氯化銨試劑變更為新配方的緩衝錯合試劑，則鹽度對吸光值 的影響大幅縮小，經過重複試驗皆呈現近似線性的鹽度干擾，只需每次測定完全 數樣本後，利用海、淡水標準品取得修正公式的斜率：
a = ( E ( SW std ) - E ( DDW std ) ) /ΔS
求得斜率後再代入還原率的修正通式中，
E ( S ) = a‧S + E ( DDW std )
依照每個樣本的鹽度及測定時的還原率，計算出鹽度修正後的還原率，代入硝酸 鹽濃度的計算，
[ NO3- ] = { ( Abs total / k NO2- ) - [ NO2- ] } / E (S)
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即可得到準確的濃度值。
以本試劑搭配自行組裝的FIA 流程板，在鎘銅管還原率測定淡水樣品約 90
%、海水樣本近 75 %的條件下，應用於淡水樣本的測定，其線性範圍之濃度上限 約為50 μM，而海水適用濃度需低於 40 μM，若感潮帶水樣中硝酸鹽的濃度高於 50 μM，則需稀釋後再測定，以免低估樣本濃度。由於河口水樣有機物質成分較高，
使得鎘銅管還原率衰減速度加快，建議每測定三個樣本之後，穿插亞硝酸鹽與硝 酸鹽的標準品，用以確認鎘銅管的還原率，便於得到準確的濃度。
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參考文獻
APHA, 1992. Standard methods for the examination of water and wastewater. 18th, Washington D. C., 4-85~4-91
Armstrong, F. A. J., 1963. Determination of nitrate in water by ultraviolet spectrophotometry. Analytical Chemistry, Vol. 35, pp. 1292
Bianchi, T., S., 2007. Biogeochemistry of estuaries. Oxford University Press, Inc. New York
Chow, T. J., Johnstone, M. S., 1962. Determination of nitrate in sea water. Analytica Chimica Acta., Vol. 27, pp. 441
Frank, J. M., 2006. Chemical oceanography. 3rd, CRC Press, pp. 305-314
Grasshoff, K., 1999. in Grasshoff, K., Ehrhardt, M., Kremling, K. eds., Methods of seawater analysis. 3rd, Verlag Chemie, Weinheim, pp. 180-186
Griess, P., 1879. Bemerkungen zu der Abhandlung der H.N. Weselky und Benedikt Ueber einege Azoverbindungen. Berichte der Deutschen chemischen Gesellschaft, Vol.
12, pp. 426-428
Head, P. C.,1985. Practical estuarine chemistry. Cambridge University Press, Inc. pp.
98-109
74
Hobbie, J. E., 2000. Estuarine science : a synthetic approach to research and practice.
Island Press, Washington DC, pp. 1-11
Jenkins, D., Medsker, L. L., 1964. Brucine method for determination of nitrate in ocean estuarine + fresh waters. Analytical Chemistry, Vol. 36, pp. 610-612
Langmuir, D., Jacobson, R. L., 1970. Specific-ion electrode determination of nitrate in some freshwater and sewage effluents. Environmental science & technology, Vol. 4, pp.
834
Libes, S. M., 1992. An introduction to marine biogeochemistry. John Wiley & Sons, Inc.
New York, pp. 154-155
Liu, K. K., Kao, S. J., Wen, L. S., Chen, K. L., 2007. Carbon and nitrogen isotopic compositions of particulate organic matter and biogeochemical processes in the eutrophic Danshuei Estuary in northern Taiwan. Science of the total environment, Vol.
382, pp. 103-120
Morris, A. W., Riley, J. P., 1963. The determination of nitrate in sea water. Analytica Chimica Acta., Vol. 29, pp. 272-279
Mullin, J. B., Riley, J. P., 1955. The spectrophotometric determination of nitrate in natural waters, with particular reference to sea-water. Analytica Chimica Acta, Vol. 12, pp. 464-480
75
Pai, S. C., Yang, C. C., 1990. Formation kinetics of pink azo dye in the determination of nitrite in natural waters. Analytica Chimica Acta, Vol. 232, pp. 345-349
Pai, S. C., Riley, J. P., 1994. Determination of nitrate in the presence of nitrite in natural waters by flow injection analysis with a non-quantitative on-line cadmium reductor.
Intern. J. Environ. Anal. Chem., Vol. 57, pp. 263-277
Riley, J. P., Chester, R., 1971. Introduction to marine chemistry. Academic Press, London, pp. 152-167
Small, H., Stevens, T. S., Bauman, W. C., 1975. Novel ion-exchange chromatographic method using conductimetric detection. Analytical Chemistry, Vol. 47, pp. 1801-1809
Stainton, M. P., 1974. Simple Efficient reduction column for use in automated determination of nitrate in water. Analytical Chemistry, Vol.46, pp. 1616
Strickland, J. T. H., Parsons, T. R., 1972. A practical handbook of sea water analysis.
2nd, Canadian Museum of Nature, Ottawa, pp. 71-76
Wood, E. D., Armstrong, F. A. J., Richards, F. A., 1967. Determination of nitrate in sea water by cadmium-copper reduction to nitrite. J. Mar. Biol. Ass. U. K., Vol. 47, pp.
23-31
江承濂, 2003. 鎘銅還原法測定水中硝酸鹽實驗條件優化暨無載流自動分析儀之設 計. 國立台灣大學理學院海洋研究所碩士論文
76
施英隆, 2000. 環境化學. 3rd, 五南圖書出版股份有限公司, 台北, pp.570
謝志強, 2007. 自助式無觸硝酸鹽分析儀之研究. 國立台灣大學理學院海洋研究所 碩士論文