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

Mark Tweedie,Paul Maguire,Brian Ward,Joao Almeida,Antonin Macquart

doi:10.1088/1361-6501/ab7405

Abstract

Continuous autonomous measurement of total dissolved inorganic carbon (TCO2) 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 CO2 with minimal reagent payload. Precise metering, suitable for sample acidification and CO2 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 mm2. Circuits based solely on asymmetric Y-junctions gave maximum meter ratios of 16:1 with a footprint of <40 mm2 and ∼0.2% precision. Further refinement is required to ensure the integrity of such small channels in integration of metering units into full TCO2 analysis microfluidic circuits.

Highlights

Abs c ontinuous and autonomous measurement of tota disso ved inorganic carbon (T O2) in the oceans is critica for mode ing important c imate change factors such as ocean uptake of atmospheric O2 and ocean acidification
Microf uidic metering circuits were constructed from variab e resistance snake channe s and dimensiona y symmetric or asymmetric Y-junctions
I o uc o Measurement of tota disso ved O2 (T O2) content in seawater by miniaturised sensors in deep sea f oats is set to become important for ong term oceanic monitoring as the oceans capture the increasing amounts of O2 re eased by fossi fue burning [ ]

Summary

Introduction

Abs c ontinuous and autonomous measurement of tota disso ved inorganic carbon (T O2) in the oceans is critica for mode ing important c imate change factors such as ocean uptake of atmospheric O2 and ocean acidification. Laser etched microf uidic snake channe restrictors and asymmetric Y meters were fabricated to adjust the metering ratio between seawater and acid simu ants.

Results

Conclusion