Photoacoustic Spectroscopy Using a Quantum Cascade Laser for Analysis of Ammonia in Water Solutions

Abstract

Ammonia (NH 3 ) toxicity, stemming from nitrification, can adversely affect aquatic life and influence the taste and odor of drinking water. This underscores the necessity for highly responsive and accurate sensors to continuously monitor NH 3 levels in water, especially in complex environments, where reliable sensors have been lacking until this point. Herein, we detail the development of a sensor comprising a compact and selective analyzer with low gas consumption and a timely response based on photoacoustic spectroscopy. This, combined with an automated liquid sampling system, enables the precise detection of ammonia traces in water. The sensor system incorporates a state-of-the art quantum cascade laser as the excitation source emitting at 9 μm in resonance with the absorption line of NH 3 located at 1103.46 cm −1 . Our instrument demonstrated detection sensitivity at a low ppm level for the ammonia molecule with response times of less than 60 s. For the sampling system, an ammonia stripping solution was designed, resulting in a prompt full measurement cycle (6.35 min). A further evaluation of the sensor within a pilot study showed good reliability and agreement with the reference method for real water samples, confirming the potential of our NH 3 analyzer for water quality monitoring applications.

Ppb-Level Ammonia Sensor for Exhaled Breath Diagnosis Based on UV-DOAS Combined with Spectral Reconstruction Fitting Neural Network

“…Nonetheless, research is still underway to address the problem of high working temperatures and to pursue a lower detection limit. On the other hand, NH 3 sensors based on optical methods mainly include gas sensors based on laser absorption spectroscopy, − gas sensors based on photoacoustic spectroscopy, gas sensors based on quartz tuning fork laser spectroscopy, gas sensors based on Fourier transform infrared spectroscopy (FTIR), and gas sensors based on ultraviolet absorption spectroscopy. − Among them, laser absorption spectroscopy-based sensors have been used for the detection of ultratrace gases due to their advantages of damage-free sample and rapid response time. However, it is challenging to avoid the interference caused by other components in EB and to further improve the measurement accuracy in the exhaled breath environment because the components of EB are complex and the concentration of breath NH 3 reaches the ppb level.…”