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

## TL;DR

A new sensor using quantum cascade laser technology detects ammonia in water with high accuracy and speed, enabling better water quality monitoring.

## Contribution

A compact, selective, and low-consumption ammonia sensor using photoacoustic spectroscopy and quantum cascade laser technology is developed.

## Key findings

- The sensor detects ammonia at low ppm levels with response times under 60 seconds.
- The system achieves full measurement cycles in 6.35 minutes using an ammonia stripping solution.
- Pilot studies confirm the sensor's reliability and agreement with reference methods for real water samples.

## Abstract

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.