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

Ammonia (NH3) 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 NH3 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 NH3 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 NH3 analyzer for water quality monitoring applications.

源于硝化作用的氨（NH₃）毒性，会对水生生物造成不利影响，同时还会改变饮用水的风味与气味。这凸显了开发高响应性、高精度传感器的迫切需求，以实现水环境中氨浓度的持续在线监测——而在复杂水体环境中，此前始终缺乏可靠的监测方案。本文详述了一款基于光声光谱法（Photoacoustic Spectroscopy）的传感器研发过程：该传感器集成了结构紧凑、选择性优异且气体消耗量极低的分析仪单元，具备快速响应特性。配合自动化液体采样系统，该传感器可实现水中痕量氨的精准检测。该传感器系统采用最先进的量子级联激光器（Quantum Cascade Laser）作为激发光源，发射波长为9μm，与氨分子位于1103.46 cm⁻¹处的特征吸收谱线实现共振匹配。本仪器对氨分子的检测灵敏度可达低ppm级别，响应时间短于60秒。针对采样系统，研究团队设计了氨汽提预处理方案，使得完整测量周期仅需6.35分钟。后续通过中试研究对该传感器进行实地评估，结果显示其针对实际水样的检测结果可靠性优异，且与标准参考方法的一致性良好，充分证实了本氨分析仪在水质监测领域的应用潜力。