膜進樣質(zhì)譜儀
美國自然基金委推薦測量濕地脫氮速率專用儀器
反硝化速率和脫氮速率科研的強大工具
高精度溶解氣體測量儀器
前言：
氮氣（N2）、氧氣（O2）、二氧化碳（CO2）是濕地、河流、湖泊、海洋等水體中的重要溶解氣體，是生態(tài)環(huán)境變化過程中的重要參數(shù)指標。例如，溶解氧是衡量海氣擴散過程、水團混合、大洋環(huán)流以及海水中生物化學過程的重要指標；水體中CO2對于研究全球碳循環(huán)和全球氣候變化具有重要作用；而水體中溶解N2則對于研究水體反硝化速率、農(nóng)業(yè)氮肥利用率、水體富營養(yǎng)化等相關問題具有至關重要的作用。目前，測量水體海洋中溶解氣體的傳統(tǒng)方法是先采集水樣，然后在實驗室內(nèi)或者船上進行檢測，但由于很多參數(shù)會隨時空的變化而發(fā)生改變，從而得不到實時原位的準確數(shù)據(jù)。水體及沉積物反硝化速率的測定方法主要有乙炔抑制法、N2通量法、質(zhì)量平衡法、化學計量法和同位素法，但這些方法大多存在人為擾動大、操作繁瑣、誤差大的不足，因而無法精確測定淹水環(huán)境下的反硝化速率。膜進樣質(zhì)譜儀（MIMS）則能夠?qū)崟r、原位、連續(xù)監(jiān)測水體中的溶解氣體（N2、O2、CO2），并且能夠精確測定淹水環(huán)境下水體、沉積物的反硝化速率，已被國內(nèi)外眾多研究機構(gòu)廣泛應用，并被美國自然科學基金委推薦用來測定濕地脫氮速率。同時，膜進樣質(zhì)譜儀還能夠應用于穩(wěn)定同位素（15N 、18O、13C）的檢測、光合呼吸、生物反應器等方面的研究。
主要特點：
- 可實時、原位檢測
- 測量精度高、重復性好
- 所需樣品量少，僅5ml
- 操作簡便，樣品分析快，僅90s
- 不需要頂空平衡，可實現(xiàn)水氣分離
- 可將空氣中高濃度背景氣體分離開，避免了樣品的污染
- 專用軟件（QuickData）高效評估收集的信號和數(shù)據(jù)
圖1 QuickData軟件
主要應用：
- 環(huán)境（水體、沉積物）反硝化速率的研究
- 原位測量水體（海洋\湖泊\河流\地表水\地下水）中O2、CH4、DMS、CO2和Ar濃度
- 海洋總初級生產(chǎn)力的測定
- 貧瘠水域的呼吸作用研究
- 穩(wěn)定同位素的測定（15N 、18O、13C）
圖2 MIMS在反硝化中的應用，將原狀沉積物和上覆水取回在室內(nèi)進行培養(yǎng)，研究反硝化過程中N2的排放速率
圖3 利用已知CH4濃度和測量出來的信號值進行擬合曲線，進而測量未知水體中CH4濃度
圖4 MIMS可用于水生生態(tài)系統(tǒng)代謝和氧氣動力學研究
圖5 MIMS可與液相氧電極或葉綠素熒光儀聯(lián)用測量光合和呼吸作用
MIMS典型應用：
表1 標樣連續(xù)測定10h后信號偏移情況（李曉波等，2013）
表2 MIMS與IRMS在測量海洋總初級生產(chǎn)力時的數(shù)據(jù)比較
圖7 利用MIMS測量出11種中國典型稻田土壤下的反硝化、厭氧氨氧化、DNRA的貢獻率（Shan J et. al, 2016）
參考文獻：
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