Measurement of Dissolved Organic Carbon in Seawater: a Comparison between the High-Temperature Catalytic Oxidation Method and the Persulfate Oxidation Method

海水中溶解性有機碳之測定：高溫催化氧化法與過硫酸氧化法之比較

洪佳章(Jia-Jang Hung) ； 張偉安(Wei-Ann Chang)

《Terrestrial, Atmospheric and Oceanic Sciences》 3卷2期 (1992/06) Pp. 165-181

摘要

本研究旨在確定高温催化氧化法之分析條件以測定海水中溶解性有機碳。此方法乃利用鉑／氧化鋁爲催化劑在680℃下分解溶解性有機碳爲二氧化碳，然後以非散性紅外光譜法測定二氧化碳之濃度。此方法之海水偵測下限在體積66μl時約爲29.5μMC，而其不準確度由數種有機物之海水添加試驗顯示約爲7%。此方法之偵測下限及精確度將因體積之增加而分別降低及增加。對於海水中溶解性有機碳之測定，高溫催化氧化法比過硫酸氧化法快速且可靠，但分析成本較高。若以高温催化氧化法於陸上實驗室進行海水分析時，海水樣本需經現場過濾，酸化及儲存於不透光之4℃中方能測得可信濃度。高溫催化氧化法測得台灣東北及西南海域海水溶解性有機碳濃度均比利用過硫酸氧化法測得之濃度高，顯示過硫酸氧化法無法完全分解海水中有機碳。高溫催化氧化法測得台灣東北海域表水之溶解性有機碳隨鹽度之降低而增加，此表示可能陸源溶解性有機碳輸入之影響所致。另一方面台灣西南海域之一測站溶解性有機碳之分佈有隨深度漸減之趨勢，暗示溶解性有機碳分佈與生物對有機物轉換之間的相關性。利用此兩種方法分析台灣東北海域水團交換影響下之溶解性有機碳分佈將有助於溶解性有機碳特性之瞭解。

並列摘要

A high-temperature catalytic oxidation method (HTCO) has been developed to measure dissolved organic carbon (DOC) in natural seawater. The method employs Pt/Al2O3 as a catalyst to oxidize DOC at 680℃ into CO2 which is detected by a nondispersive IR detector. The detection limit of the method was estimated to be 29.5 μMC on the basis of a sample volume of 66 μl. The precision was generally better than 7%with respect to selected organics added to natural seawater. The detection limit and precision are expected to be lower and greater, respectively, if the injection volume is increased. The HTCO method is faster, more reliable, but higher in analytical cost than the persulfate oxidation method for the analysis of DOC in seawater samples. To obtain reliable values of DOC in a land laboratory, the seawater sample should be filtered, acidified and stored at 4℃ immediately after sampling. The HTCO method measured the higher values of DOC than did the persulfate method in shelf waters off northeastern and southwestern Taiwan, indicating the incomplete oxidation of the persulfate method. The persulfate method, however, is still recommended for use along with the HTCO method because each method for analyzing DOC provides different geochemical information. The DOC value increases as salinity decreases in surface water off northeastern Taiwan reflecting the influence of terrestrial sources on the distribution of DOC. A vertical decrease of DOC with depth was also found at a station off southwestern Taiwan, indicating that there may be a relationship between DOC distribution and biological turn over of organic carbon. The priorities extended from this study will focus on the spatial and temporal distributions of DOC and their geochemical significance reflected from the use of both methods for marginal seawater under the influence of the Kuroshio.