High-frequency measurement of partial pressure and total concentration of carbon dioxide in seawater using microporous hydrophobic membrane contactors
High-frequency measurement of partial pressure and total concentration of carbon dioxide in seawater using microporous hydrophobic membrane contactors
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DOI：
10.4319/lom.2004.2.356
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发表时间：
2004-11-01
影响因子：
2.7
通讯作者：
Takahashi, T
中科院分区：
文献类型：
--
作者：
Hales, B;Chipman, D;Takahashi, T
为了以更高的时空分辨率研究海水中的二氧化碳化学，我们开发了海水中二氧化碳分压(P-CO2)和总二氧化碳浓度(T-CO2)的测量系统，该系统具有最先进的精度，但分析频率增加了一个数量级或更高。P-CO2系统的基础是利用工业应用中通常使用的商用膜接触器装置，将流动海水样品流中的无二氧化碳载气与含水二氧化碳进行平衡，然后对出口载气中的二氧化碳进行非分散红外(NDIR)吸收检测。T-CO2系统基于向酸性(0.1N HCl)液体载流中注入小体积海水样品回路(类似于1毫升)，以将所有碳酸盐和重碳酸盐离子转化为含水的二氧化碳；然后将酸化样品通过定制的小体积膜接触器单元，其中样品的P-CO2通过无CO2载气的平衡和NDIR检测来确定。给出了在南极洲罗斯海波利尼亚进行的实验室测试和野外实验的结果。经测定，P-CO_2系统的响应时间约为S的3倍，精密度优于1微米。T-CO_2系统的最大分析速率为每36个S一个样品，重现性在几个小时内优于0.2%。
To investigate CO2 chemistry in ocean water with greater time-space resolutions, we developed measurement systems, which have state-of-the-art precision but an order of magnitude or better increase in the frequency of analysis, for carbon dioxide partial pressures (P-CO2) and total carbon dioxide concentrations (T-CO2) in seawater. The P-CO2 system was based on equilibration of a CO2-free carrier gas stream with aqueous carbon dioxide in a flowing seawater sample stream using a commercially available membrane contactor unit normally employed in industrial applications followed by nondispersive infrared (NDIR) absorbance detection of the CO2 in the exit carrier gas. The T-CO2 system was based on injection of a small-volume seawater sample loop (similar to1 mL) into an acid (0.1 N HCl) liquid carrier stream to convert all carbonate and bicarbonate ions to aqueous carbon dioxide; this acidified sample was then passed through a custom-made small-volume membrane contactor unit where the sample's P-CO2 was determined by equilibration of a CO2-free carrier gas followed by NDIR detection. Results from lab tests and a field experiment in the Ross Sea polynya, Antarctica, are presented. The P-CO2 system was determined to have a response time of about 3 s and precision of better than 1 muatm. The T-CO2 system had a maximum analysis rate of one sample per 36 s, and reproducibility was determined to be better than 0.2% for a period of hours.