Bhattacharya, Sayoni, Esposito, Mario, Tanhua, Toste and Achterberg, Eric P. (2024) Development of an autonomous on-site dissolved inorganic carbon analyzer using conductometric detection. Analytica Chimica Acta, 1307 . Art.Nr. 342610. DOI 10.1016/j.aca.2024.342610.

Preview	Text 1-s2.0-S0003267024004112-main.pdf - Published Version Available under License Creative Commons: Attribution-Noncommercial 4.0. Download (8MB) | Preview
	Text 1-s2.0-S0003267024004112-mmc1.docx - Supplemental Material Available under License Creative Commons: Attribution-Noncommercial 4.0. Download (4MB)

Abstract

Highlights

• Development of an autonomous DIC analyzer based on Conductometric technique using a cell with 4 hollow brass electrodes.
• CO2 extraction from seawater using a gas diffusion cell with a “Tube In A Tube” configuration and a gas permeable membrane.
• Formulation of mathematical temperature and salinity correction to determine accurate DIC concentration.
• Demonstration of the analyzer performance in the southwest Baltic Sea.

Abstract

Background

The increase in anthropogenic CO2 concentrations in the Earth's atmosphere since the industrial revolution has resulted in an increased uptake of CO2 by the oceans, leading to ocean acidification. Dissolved Inorganic Carbon (DIC) is one of the key variables to characterize the seawater carbonate system. High quality DIC observations at a high spatial-temporal resolution is required to improve our understanding of the marine carbonate system. To meet the requirements, autonomous DIC analyzers are needed which offer a high sampling frequency, are cost-effective and have a low reagent and power consumption.

Results

We present the development and validation of a novel analyzer for autonomous measurements of DIC in seawater using conductometric detection. The analyzer employs a gas diffusion sequential injection approach in a “Tube In A Tube” configuration that facilitates diffusion of gaseous CO2 from an acidified sample through a gas permeable membrane into a stream of an alkaline solution. The change in conductivity in the alkaline medium is proportional to the DIC concentration of the sample and is measured using a detection cell constructed of 4 hollow brass electrodes. Physical and chemical optimizations of the analyzer yielded a sampling frequency of 4 samples h−1 using sub mL reagent volumes for each measurement. Temperature and salinity effects on DIC measurements were mathematically corrected to increase accuracy. Analytical precision of ±4.9 μmol kg−1 and ±9.7 μmol kg−1 were achieved from measurements of a DIC reference material in the laboratory and during a field deployment in the southwest Baltic Sea, respectively.

Significance

This study describes a simple, cost-effective, autonomous, on-site benchtop DIC analyzer capable of measuring DIC in seawater at a high temporal resolution as a step towards an underwater DIC sensor. The analyzer is able to measure a wide range of DIC concentrations in both fresh and marine waters. The achieved accuracy and precision offer an excellent opportunity to employ the analyzer for ocean acidification studies and CO2 leakage detection in the context of Carbon Capture and Storage operations.

Actions (login required)

View Item