Metered reagent injection into microfluidic continuous flow sampling for conductimetric ocean dissolved inorganic carbon sensing

• Published in: Measurement Science and Technology
• Main Authors: Tweedie, Mark, Macquart, Antonin, Almeida, Joao, Ward, Brian, Maguire, Paul
• Other Authors: The Department of Employment and Learning, N. Ireland, Invest N. Ireland, National Science Foundation, Science Foundation Ireland
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: IOP Publishing 2020
• Subjects: Ocean acidification
• Online Access: http://dx.doi.org/10.1088/1361-6501/ab7405; https://iopscience.iop.org/article/10.1088/1361-6501/ab7405; https://iopscience.iop.org/article/10.1088/1361-6501/ab7405/pdf

Abstract Continuous autonomous measurement of total dissolved inorganic carbon (TCO 2 ) in the oceans is critical for climate change modelling and ocean acidification measurement. A microfluidic conductivity-based approach will permit integration of miniaturised chemical analysis systems into Argo ocean floats, for long-term, high-accuracy depth profiling of dissolved CO 2 with minimal reagent payload. Precise metering, suitable for sample acidification and CO 2 liberation, is addressed. Laser etched microfluidic snake channel restrictors and asymmetric Y-meters were fabricated, with channel dimensions down to ∼75 μm, to adjust metering ratios between seawater and acid simulants. Hydrodynamic resistances, from flow versus pressure measurements, were compared with finite element simulations for various cross-section profiles and areas. Microfluidic metering circuits were constructed from various resistance snake channels and Y-junction components. Sample to acid volume ratios (meter ratio) up to 100:1 have been achieved with 300 μm wide snake channels for lengths >m. At highest resolution, the footprint would be >600 mm 2 . Circuits based solely on asymmetric Y-junctions gave maximum meter ratios of 16:1 with a footprint of <40 mm 2 and ∼0.2% precision. Further refinement is required to ensure the integrity of such small channels in integration of metering units into full TCO 2 analysis microfluidic circuits.