Autonomous continuous analysis of oceanic dissolved inorganic carbon (DIC) concentration with depth is of great significance with regard to ocean acidification and climate change. However, miniaturisation of in situ analysis systems is hampered by the size, cost and power requirements of traditional optical instrumentation. Here, we report a low-cost microfluidic alternative based on CO2 separation and conductance measurements that could lead to integrated lab-on-chip systems for ocean float deployment, or for moored or autonomous surface vehicle applications. Conductimetric determination of concentration, in the seawater range of 1000-3000 µmol kg-1, has been achieved using a microfluidic thin-film electrode conductivity cell and a membrane-based gas exchange cell. Sample acidification released CO2 through the membrane, reacting in a NaOH carrier, later drawn through a sub-µL conductivity cell, for impedance versus time measurements. Precision values (relative standard deviations) were ~ 0.2% for peak height measurements at 2000 µmol kg-1. Comparable precision values of ~ 0.25% were obtained using a C4D electrophoresis headstage with similar measurement volume. The required total sample and reagent volumes were ~ 500 µL for the low volume planar membrane gas exchange cell. In contrast, previous conductivity-based DIC analysis systems required total volumes between 5000 and 10,000 µL. Long membrane tubes and macroscopic wire electrodes were avoided by incorporating a planar membrane (PDMS) in the gas exchange cell, and by sputter deposition of Ti/Au electrodes directly onto a thermoplastic (PMMA) manifold. Future performance improvements will address membrane chemical and mechanical stability, further volume reduction, and component integration into a single manifold.

中文翻译：

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使用带有膜分离CO2的微流电导率传感器分析液体中溶解的无机碳。

在深度上自主连续分析海洋溶解无机碳（DIC）的浓度对于海洋酸化和气候变化具有重要意义。然而，传统光学仪器的尺寸，成本和功率要求阻碍了原位分析系统的小型化。在这里，我们报告了一种基于CO2分离和电导率测量的低成本微流体替代品，该替代品可能会导致集成的片上实验室系统用于海洋漂浮物部署，系泊或自动地面车辆应用。使用微流控薄膜电极电导池和基于膜的气体交换池，可以在1000-3000 µmol kg-1的海水范围内进行电导浓度测定。样品酸化通过膜释放出CO2，在NaOH载体中反应，后来通过亚µL电导率电池抽取，用于阻抗与时间的测量。对于在2000 µmol kg-1处的峰高测量，精度值（相对标准偏差）为〜0.2％。使用具有相似测量体积的C4D电泳探头，可获得约0.25％的可比较精度值。小体积平面膜气体交换池所需的样品和试剂总量约为500 µL。相反，以前的基于电导率的DIC分析系统需要的总体积为5000至10,000 µL。通过在气体交换室中加入平面膜（PDMS），以及将Ti / Au电极直接溅射沉积到热塑性塑料（PMMA）歧管上，可以避免使用长膜管和宏观丝电极。