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Description:

The detection of ammonia (NH3) and volatile fatty acids (VFAs) during anaerobic
processes plays an important role in the management of livestock and their waste, as well as
in biogas production. A newly developed moisture sensor chip (MSC) was used to monitor
these gasses volatized from aqueous solutions. The concentrations of NH3, acetic acid (AA),
propionic acid (PA), and butyric acid (BA) were in the range 60–150 mM. To substantially
improve the detection sensitivity, MSC was cooled from 24 to 19 °C. Because the
temperature was decreased, volatized water and solute condensed on the surface of the MSC
and the formed microdroplets and the detection current increased to several thousand
picoamperes. The detection current also increased with increasing concentration of VFAs
and was highly sensitive to the pH conditions and the partial pressure of VFAs in the air
phase. The applicable concentration range was from 0 to 150 mM for NH3 and from 60 to
150 mM for VFAs. The highest sensor sensitivity to NH3 was 12.3 mM-1 at 22 °C. The
highest sensor sensitivity for AA among VFAs was 4.0 mM-1 at 19 °C. The amount of water
droplets formed on the surface of MSC increased with increasing pH of the aqueous solution
in the order NH3>water>VFAs. Droplet formation preferentially occurred in the order
AA>PA>BA, indicating that a shorter alkyl chain of VFA was preferred. The proposed
temperature-controlled MSC is applicable for the detection of NH3 under basic conditions
and for the detection of VFAs under acidic conditions.

Rights:

• In Copyright
  

Keyword: VFA sensor

Date published: 2025-06-01

Publisher: Elsevier BV

Journal:

• SENSORS AND ACTUATORS B-CHEMICAL (ISSN: 09254005) vol. 442 138077

Funding:

• Japan Society for the Promotion of Science 22H02149
• Japan Science and Technology Agency Moonshot Research and Development Program JPJ009237

Manuscript type: Author's version (Submitted manuscript)

MDR DOI: https://doi.org/10.48505/nims.5574

First published URL: https://doi.org/10.1016/j.snb.2025.138077

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Updated at: 2025-07-11 08:30:37 +0900

Published on MDR: 2025-07-11 08:16:38 +0900