Spectrophotometric pH Analyzer Developed for Ocean Acidification Research

By Usman AhmedOct 21 2022Reviewed by Laura Thomson

A recent study published in Sensors demonstrates the development of a handheld pH instrument named pHyter. The researchers determined the accuracy of pH measurements made using the pHyter compared with desktop spectrophotometric seawater pH measurements and electrochemical sensors.

Ocean Acidification

Atmospheric carbon dioxide (CO₂) levels increased from 280 parts per million volume in preindustrial times to 420 parts per million volume in 2022. Oceans contribute significantly to regulating CO₂ concentrations through atmospheric uptake. The oceans absorb nearly a third of the anthropogenic carbon released into the atmosphere. This ocean absorption of CO₂ results in ocean acidification.

The process of introducing CO₂ into the ocean results in the formation of carbonic acid and lowers ocean pH. Ocean acidification (OA) negatively influences the biochemical cycles and modifies chemical equilibria and physiological processes of marine creatures all over the world's oceans. Wide-ranging pH measurement is challenging because accurate pH measurement equipment is expensive, heavy, and complicated.

Effect of pH Reduction on Ocean Environment

Abrupt pH variations influence the chemical composition of natural water as a governing factor in aqueous chemical equilibrium, potentially impacting crucial physiological processes. The pH decrease in ocean ecosystems substantially affects calcium carbonate saturation, which is a proxy for the capacity of calcifying organisms to form shells and the continuation of carbon sequestration.

Ocean pH is a proxy for biological productivity through the inorganic carbon cycle in natural aquatic systems. It is essential to comprehend and track these environmental changes for research on the health of the marine ecosystem, fisheries, and climate.

Constraints in Monitoring of pH Variations and Ocean Acidification

The global impacts of ocean acidification and its implications for the total carbon budget remain inadequately defined due to a lack of monitoring of the proper spatial and temporal dimensions. The leading causes of infrequent monitoring of pertinent geographical and temporal timescales are lack of technical training, difficulty taking precise pH readings, and expensive equipment for accurate measurements.

Even though biological activity alone can cause pH fluctuations in coastal areas of up to one pH unit, human factors such as sewage or industrial discharge also frequently amplify these variations. It is challenging to track, comprehend, and interpret these changes because pH can vary significantly within local regions without the widespread availability of pH measurement instruments.

Current Methods of pH Measurements

A wide range of spectrophotometric laboratory techniques, electrochemical sensors, and spectrophotometric in-situ techniques are used to measure pH. Traditional glass electrodes, extended gate field effect transistors, and ion-sensitive field effect transistors are examples of electrochemical sensors.

Spectrophotometric pH analysis is preferred for seawater measurements due to its high precision, long-term stability, and accuracy. In situ analyzers, such as the Submersible Autonomous Moored Instruments (SAMI), which take stable and accurate pH measurements when placed in marine environments, can also be used.

Need for Simple and Portable Equipment for pH Measurements and Ocean Acidification Investigation

Electrochemical sensors used for measuring pH are often low-performing and expensive. Skilled scientists must deploy, maintain, use, and recover the devices. Simple, inexpensive, handheld spectrophotometric pH equipment that can accurately measure pH is required for ocean acidification investigations.

Such instruments are not widely employed since most scientists working on ocean acidification lack the time or funding to construct them. Due to limitations in the current pH instruments on the market, many people who live near the coast can still not access pH measurements.

Development of a Simple Handheld pH Meter for Monitoring pH

Pardis et al. developed a portable, inexpensive pH meter (pHyter). The pHyter design was based on mCP chemistry and had the properties needed for field measurements of aquatic pH, such as sturdiness, self-contentedness, portability, and wireless operation. It was specifically made for effective commercial manufacture. The pHyter was tested and validated using analytical laboratory characterizations and field deployments in North America and the South Pacific.

Research Findings

An alternative strategy from the usual scientist-centric data-gathering model is required to expand geographical and temporal pH monitoring. There are coastal communities worldwide that are invested in their local surroundings and have invaluable local expertise, but they do not currently have the resources to monitor their waterways.

The researchers developed and verified a novel pH meter for measuring coastal pH in this study. The pHyter was comparable in accuracy to inter-laboratory spectrophotometric pH readings. Its readings had an average pH accuracy and precision of +0.026 ± 0.045 pH. The pH difference between tabletop spectrophotometric readings and pHyter measurements of seawater ranged from 0.001 to 0.010. Finally, a pH difference of 0.033 ± 0.066 was found on a reef in the South Pacific when in situ iSAMI and pHyter pH readings were compared.

This accuracy is a significant improvement over the electrochemical probe-based pH measurement that is currently used, where accuracy in seawater can drop as low as ±0.2 without rigorous calibration to spectrophotometric pH. The pHyter can help individuals worldwide get the same understanding of the pH patterns of their local waters that scientists can realize with more sophisticated equipment at a cheaper cost.

Reference

Pardis, W., Grabb, K. C., DeGrandpre, M. D., Spaulding, R., Beck, J., Pfeifer, J. A., & Long, D. M. (2022) Measuring Protons with Photons: A Hand-Held, Spectrophotometric pH Analyzer for Ocean Acidification Research, Community Science and Education. Sensors, 22(20), Article 20. https://www.mdpi.com/1424-8220/22/20/7924

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