An Automated Microfluidic Analyzer for In Situ Monitoring of Total Alkalinity.

Area of Science:

• Oceanography
• Environmental Science
• Analytical Chemistry

Background:

• Understanding the ocean carbon cycle is vital for addressing anthropogenic carbon dioxide (CO2) uptake.
• Ocean alkalinity enhancement is a proposed method for carbon dioxide removal, requiring robust monitoring.
• Accurate, long-term measurements of seawater total alkalinity are essential for these efforts.

Purpose of the Study:

• To design, build, test, and deploy an autonomous in situ analyzer for seawater total alkalinity.
• To provide a lightweight, reagent-efficient instrument for long-term oceanographic deployments.
• To enable high-resolution, affordable observations of a key ocean carbon system parameter.

Main Methods:

• Developed a microfluidic, autonomous analyzer utilizing closed-cell titrations.
• Employed three independent stepper-motor driven syringe pumps for precise reagent mixing.
• Characterized temperature effects (5-25 °C) and validated performance with field data and certified reference materials.

Main Results:

• The autonomous analyzer demonstrated high accuracy (-0.17 ± 24 μmol kg-1) and precision (16 μmol kg-1) in field deployments.
• Each titration point required minimal sample volume (830 μL), titrant (170 μL), energy (460 J), and time (105 s).
• Successful 25-day cumulative operation across two field sites validated the instrument's reliability.

Conclusions:

• The developed autonomous in situ total alkalinity analyzer is suitable for long-term, remote ocean monitoring.
• This technology facilitates affordable, high-resolution observations critical for ocean carbon cycle research and carbon dioxide removal verification.
• The instrument's microfluidic design enhances its utility for various oceanographic platforms.