Autonomous in situ measurements of freshwater alkalinity

Shangguan, Qipei; Lai, Chaohua; Beatty, Cory M.; Young, Fischer L.; Spaulding, Reggie S.; DeGrandpre, Michael D.

doi:10.1002/lom3.10404

Cited by 10 publications

(14 citation statements)

References 62 publications

(121 reference statements)

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“…Some approaches for continuous measurements of alkalinity have been investigated in recent years. 17 with pH indicators was utilized to provide colorimetric detection, with the signals being rather sensitive to certain interferences (such as suspended particles and colored dissolved organic carbon compounds). Also, it seems that this class of system is more suitable for near-surface operation; even they may offer in situ measurements in both freshwater and seawater.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Also, it seems that this class of system is more suitable for near-surface operation; even they may offer in situ measurements in both freshwater and seawater. 17,18 Although these systems are truly miniaturized in comparison with conventional titration methodologies, as well as presenting some degree of autonomy, a reagentless methodology would be beneficial to provide depthbased alkalinity profiling. Furthermore, readouts other than optical ones may result in measurements with less interferences.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Some approaches for continuous measurements of alkalinity have been investigated in recent years. , Reagent mixing with pH indicators was utilized to provide colorimetric detection, with the signals being rather sensitive to certain interferences (such as suspended particles and colored dissolved organic carbon compounds). Also, it seems that this class of system is more suitable for near-surface operation; even they may offer in situ measurements in both freshwater and seawater. , Although these systems are truly miniaturized in comparison with conventional titration methodologies, as well as presenting some degree of autonomy, a reagentless methodology would be beneficial to provide depth-based alkalinity profiling. Furthermore, readouts other than optical ones may result in measurements with less interferences.…”

Section: Introductionmentioning

confidence: 99%

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Reagentless Acid–Base Titration for Alkalinity Detection in Seawater

et al. 2021

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Herein, we report on a reagentless electroanalytical methodology for automatized acid−base titrations of water samples that are confined into very thin spatial domains. The concept is based on the recent discovery from our group (Wiorek, A. et al. Anal. Chem. 2019, 91, 14951−14959), in which polyaniline (PANI) films were found to be an excellent material to release a massive charge of protons in a short time, achieving hence the efficient (and controlled) acidification of a sample. We now demonstrate and validate the analytical usefulness of this approach with samples collected from the Baltic Sea: the titration protocol indeed acts as an alkalinity sensor via the calculation of the proton charge needed to reach pH 4.0 in the sample, as per the formal definition of the alkalinity parameter. In essence, the alkalinity sensor is based on the linear relationship found between the released charge from the PANI film and the bicarbonate concentration in the sample (i.e., the way to express alkalinity measurements). The observed alkalinity in the samples presented a good agreement with the values obtained by manual (classical) acid−base titrations (discrepancies <10%). Some crucial advantages of the new methodology are that titrations are completed in less than 1 min (end point), the PANI film can be reused at least 74 times over a 2 week period (<5% of decrease in the released charge), and the utility of the PANI film to even more decrease the final pH of the sample (pH ∼2) toward applications different from alkalinity detection. Furthermore, the acidification can be accomplished in a discrete or continuous mode depending on the application demands. The new methodology is expected to impact the future digitalization of in situ acid−base titrations to obtain high-resolution data on alkalinity in water resources.

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Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reagentless Acid–Base Titration for Alkalinity Detection in Seawater

et al. 2021

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“…24 Despite the rapid progress in alkalinity analyzer development, encouraged and sustained by the demand for carbon cycle and OAE studies, there remains a need for a rugged, miniaturized, cost-effective autonomous instrument. To the authors' knowledge, field ruggedness has been a particular challenge in instrument development, with the SAMI-alk system reporting field data for no more than 23 consecutive days 9 and the ISFET systems showing 6 days of continuous field data. 22 Microfluidic in situ platforms are a proven technology for autonomous sensors in ocean environments.…”

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confidence: 99%

An Automated Microfluidic Analyzer for In Situ Monitoring of Total Alkalinity

et al. 2023

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We have designed, built, tested, and deployed an autonomous in situ analyzer for seawater total alkalinity. Such analyzers are required to understand the ocean carbon cycle, including anthropogenic carbon dioxide (CO2) uptake and for mitigation efforts via monitoring, reporting, and verification of carbon dioxide removal through ocean alkalinity enhancement. The microfluidic nature of our instrument makes it relatively lightweight, reagent efficient, and amenable for use on platforms that would carry it on long-term deployments. Our analyzer performs a series of onboard closed-cell titrations with three independent stepper-motor driven syringe pumps, providing highly accurate mixing ratios that can be systematically swept through a range of pH values. Temperature effects are characterized over the range 5–25 °C allowing for field use in most ocean environments. Each titration point requires approximately 170 μL of titrant, 830 μL of sample, 460 J of energy, and a total of 105 s for pumping and optical measurement. The analyzer performance is demonstrated through field data acquired at two sites, representing a cumulative 25 days of operation, and is evaluated against laboratory measurements of discrete water samples. Once calibrated against onboard certified reference material, the analyzer showed an accuracy of −0.17 ± 24 μmol kg–1. We further report a precision of 16 μmol kg–1, evaluated on repeated in situ measurements of the aforementioned certified reference material. The total alkalinity analyzer presented here will allow measurements to take place in remote areas over extended periods of time, facilitating affordable observations of a key parameter of the ocean carbon system with high spatial and temporal resolution.

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“…Long-duration time series of TA data are important for the investigation of carbonate chemistry related to biogeochemical processes in the ocean. The duration of field deployments with the reported analyzers has been limited, with 23 days of TA data for the SAMI-alk; 29 6 days for the dual pH-A T sensor during a continuous deployment in Ka ̅ ne'ohe Bay; 27 and 15 days of field data for the microfluidic TA analyzer. 28 Despite the great advances made in recent years, improving the performance of in situ TA analyzers/sensors, particularly in terms of precision, accuracy, and duration of field deployment, remains a major challenge.…”

mentioning

confidence: 99%

High-Precision In Situ Total Alkalinity Analyzer Capable of Month-Long Observations in Seawaters

Qiu

Yuan

et al. 2023

ACS Sens.

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Total alkalinity (TA) is an essential variable for the study of physical and biogeochemical processes in coastal and oceanic systems, and TA data obtained at high spatiotemporal resolutions are highly desired. The performance of the current in situ TA analyzers/sensors, including precision, accuracy, and deployment duration, cannot fully meet most research requirements. Here, we report on a novel high-precision in situ analyzer for surface seawater TA (ISA-TA), based on an automated single-point titration with spectrophotometric pH detection, and capable of long-term field observations. The titration was carried out in a circulating loop, where the titrant (a mixture of HCl and bromocresol green) and seawater sample were mixed in a constant volume ratio. The effect of ambient temperature on the TA measurement was corrected with an empirical formula. The weight, height, diameter, and power consumption of ISA-TA were 8.6 kg (in air), 33 cm, 20 cm, and 7.3 W, respectively. A single measurement required ∼7 min of running time, ∼32 mL of seawater, and ∼0.6 mL of titrant. ISA-TA was able to operate continuously in the field for up to 30 days, and its accuracies in the laboratory and field were 0.5 ± 1.7 μmol kg–1 (n = 13) and 10.3 ± 2.8 μmol kg–1 (n = 29) with precisions of 0.6–0.8 μmol kg–1 (n = 51) and 0.2–0.7 μmol kg–1 (n = 8), respectively. This study provides the research community with a new tool to obtain seawater TA data of high temporal resolution.

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Autonomous in situ measurements of freshwater alkalinity

Cited by 10 publications

References 62 publications

Reagentless Acid–Base Titration for Alkalinity Detection in Seawater

Reagentless Acid–Base Titration for Alkalinity Detection in Seawater

An Automated Microfluidic Analyzer for In Situ Monitoring of Total Alkalinity

High-Precision In Situ Total Alkalinity Analyzer Capable of Month-Long Observations in Seawaters

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