Optical sensor for continuous free chlorine and chloramine monitoring in water

Overview

This solution addresses a long-standing limitation in water quality monitoring: the subjectivity and poor repeatability of colorimetric strip tests for free chlorine and chloramine. By immobilizing colorimetric probe compounds within a transparent inorganic polymer matrix and integrating them into a flow channel, the technology enables continuous optical measurement of these disinfectants. A compact multi-band optical device paired with multivariate analysis algorithms converts the optical response into reliable concentration readings, removing the variability introduced by manual interpretation of color changes.

The approach is well suited to drinking water treatment, distribution networks, industrial process water, and aquaculture, where accurate and continuous disinfectant residual monitoring is critical for safety and regulatory compliance.

Technical specifications

Key features:

• Colorimetric probes for free chlorine and chloramine immobilized in a transparent sol-gel matrix for stability and reusability
• Flow-channel integration allowing continuous contact between the water sample and the immobilized probes
• Compact multi-band optical device capturing spectral response across multiple wavelengths
• Multivariate regression algorithms that convert spectral data into accurate concentration estimates
• Design philosophy adapted from established process analytical technology (PAT) used in industrial sectors such as dairy processing

How it works:

The immobilized probes react with target analytes in the flowing water, producing a measurable color change. The optical device records the resulting spectrum, and the multivariate model interprets the multi-wavelength response to output a concentration value, reducing interference and improving accuracy compared with single-wavelength or visual readings.

Technology readiness level

The underlying combination of multi-band optical sensing and multivariate analysis has been demonstrated in a prior industrial collaboration for continuous protein measurement in dairy processing, confirming the feasibility of the methodology. Current development focuses on preparing sol-gel materials with immobilized chlorine and chloramine probes, training and validating the multivariate regression model using solutions of known concentration, and then constructing a bespoke sensor from available optical components. The technology is at an early-to-mid stage of development, transitioning from laboratory proof-of-concept toward a functional sensor prototype.