膜進(jìn)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(qiáng)大工具
高精度溶解氣體測量儀器
前言：
氮?dú)猓∟2）、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(biāo)。例如，溶解氧是衡量海氣擴(kuò)散過程、水團(tuán)混合、大洋環(huán)流以及海水中生物化學(xué)過程的重要指標(biāo)；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(guān)問題具有至關(guān)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(shí)驗(yàn)室內(nèi)或者船上進(jìn)行檢測，但由于很多參數(shù)會(huì)隨時(shí)空的變化而發(fā)生改變，從而得不到實(shí)時(shí)原位的準(zhǔn)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(xué)計(jì)量法和同位素法，但這些方法大多存在人為擾動(dòng)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(jìn)樣質(zhì)譜儀（MIMS）則能夠?qū)崟r(shí)、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(jī)構(gòu)廣泛應(yīng)用，并被美國自然科學(xué)基金委推薦用來測定濕地脫氮速率。同時(shí)，膜進(jìn)樣質(zhì)譜儀還能夠應(yīng)用于穩(wěn)定同位素（15N 、18O、13C）的檢測、光合呼吸、生物反應(yīng)器等方面的研究。
主要特點(diǎn)：
- 可實(shí)時(shí)、原位檢測
- 測量精度高、重復(fù)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(shí)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(yīng)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(yīng)用，將原狀沉積物和上覆水取回在室內(nèi)進(jìn)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(jìn)行擬合曲線，進(jìn)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(dòng)力學(xué)研究
圖5 MIMS可與液相氧電極或葉綠素?zé)晒鈨x聯(lián)用測量光合和呼吸作用
MIMS典型應(yīng)用：
表1 標(biāo)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(shí)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(xiàn)率（Shan J et. al, 2016）
參考文獻(xiàn)：
1.李曉波, 夏永秋, 郎漫, 等. N2：Ar法直接測定淹水環(huán)境反硝化產(chǎn)物N2的產(chǎn)生速率. 農(nóng)業(yè)環(huán)境科學(xué)學(xué)報(bào), 2013, 32(6): 1284-1288
2.趙永強(qiáng), 夏永秋, 李博倫, 等. 利用膜進(jìn)樣質(zhì)譜同時(shí)測定河流沉積物反硝化和厭氧氨氧化. 農(nóng)業(yè)環(huán)境科學(xué)學(xué)報(bào), 2014, 33(4): 794-802
3.Alexandra M F R, Matthew A C. Benthic nitrogen fixation in an eutrophic estuary affected by groundwater discharge. Journal of Coastal Research, 2012, 28(2): 477-485
4. Alexander J R, Jennifer L T, Timothy J H, et al. Sediment, water column, and open-channel denitrification in rivers measured using membrane-inlet mass spectrometry. Journal of Geophysical Research: Biogeosciences, 2015, 121: 1258 -1274
5.Fred J G, Dragoslav T M, John C L. Estimating rates of denitrification enzyme activity in wetland soils with direct simultaneous quantification of nitrogen and nitrous oxide by membrane inlet mass spectrometry. Microbial & Biochemical Technology, 2013, 5(4): 095-101
6. Gueguen C, Tortell P D. High-resolution measurement of Southern Ocean CO2 and O2/Ar by membrane inlet mass spectrometry[J]. Marine Chemistry, 2008, 108(3/4): 184-194
7. Jeffrey C C, Michael K, Todd M K. Denitrification in coastal ecosystems: methods, environmental controls, and ecosystem level controls, a review. Aquatic Ecology, 1999, 33: 41-54
8. Jun S, Xu Z, Rong S, et al. Dissimilatory nitrate reduction processes in typical Chinese paddy soils: rates, relative contributions, and influencing factors. Environmental Science & Technology, 2016, 50: 9972-9980
9. Kaiser J, Reuer M K, Barnett B, et al. Marine productivity estimates from continuous O2/Ar ratio measurements bymembrane inlet mass spectromtry[J]. Geophysical Reasearch Letters, 2005, 32(19), doi: 10. 1029/2005GL023459
10. Ketil K J, Anne E G. New approach for measuring denitrification in the rhizosphere of vegetated marsh sediments. Limnology and Oceanography: Methods, 2009, 7: 626-637
11. Lesley K S, Mary A V, John K B, et al. Denitrification in nitrate-rich streams: application of N2:Ar and 15N-tracer methods in intact cores. Eeological Applications, 2006, 16(6): 2191-2207
12. Mohammad L K, Karl G R. Denitrification enzyme activity and potential of subsoils under grazed grasslands assayed by membrane inlet mass spectrometer. Soils Biology & Biochemistry, 2011, (43):1787-1797
13. Peter M G, Mark A A, Bohlke J K, et al. Methods for measuring denitrification: diverse approaches to A difficult problem. Ecological Applications, 2006, 16(6): 2091-2122
14. Reisinger A J, Tank J L, Hoellein T J, et al. Sediment, water column, and open‐channel denitrification in rivers measured using membrane‐inlet mass spectrometry[J]. Journal of Geophysical Research: Biogeosciences, 2016, 121(5): 1258-1274
15. Sara F, Daniela A V, Karin M B, et al. Application of membrane inlet mass spectrometry to measure aquatic gross primary production by the 18O in vitro method. Limnology and Oceanography: Methods, 2016, 14: 610-622
16. Shan J, Zhao X, Sheng R, et al. Dissimilatory nitrate reduction processes in typical Chinese paddy soils: rates, relative contributions, and influencing factors. Environmental Sciences & Technology, 2016, 50: 9972-9980
17. Sooomo A, Wayne S G, Todd M K. Simultaneous measurement of denitrification and nitrogen fixation using isotope pairing with membrane inlet mass spectrometry analysis. Applied and Environmental Microbiology, Mar. 2001, p. 1171-1178
18. Todd M K, Christina D, Hunt D, et al. Membrane inlet mass spectrometer for rapid high-precision determination of N2, O2, and Ar in environmental water samples. Analytical Chemistry, 1994, 66(23): 4166-4170
19. Todd K M, Cornwell J C, Zhong L. Determination of denitrification in the Chesapeake Bay from measurements of N2 accumulation in bottom water[J]. Estuaries and Coasts, 2006, 29(2): 222-231.
20. Todd M K, Matthew B S, Jeffrey C C, et al. Denitrification in estuarine sediments determined by membrane inlet mass spectrometry. Limnology and Oceanography, 1998, 43(2): 334-339
21. Tortell P D. Dissolved gas measurements in oceanic waters made by membrane inlet mass spectrometry[J]. Limnology and Oceanography: Methods, 2005, 3(1): 24-37
22. Zhou W, Xia L L, Yan X Y. Vertical distribution of denitrification end-products in paddy soils. Science of the Total Environment, 2017, 576: 462-471
23. Li X B, Xia L L, Yan X Y. Application of membrane inlet mass spectrometry to directly quantify denitrificaion in flooded rice paddy soil. Biology and Fertility of Soils, 2014, 50(6): 1-10
24. Zhao Y Q, Xia Y Q, Ti C P, et al. Nirtrogen removal capacity of the river network in a high nitrogen loading region. Environmental Science and Technology, 2015, 49(3): 1427-1435
