Color QR Codes for Smartphone-Based Analysis of Free Chlorine in Drinking Water

Area of Science:

• Analytical Chemistry
• Computer Vision
• Water Quality Monitoring

Background:

• Free chlorine (FC) is essential for drinking water safety, but traditional measurement methods are often impractical for real-time, on-site use.
• Existing methods for FC detection, such as BTB strips and DPD powder tests, rely on visual colorimetric comparisons.
• QR Codes, typically used for data encoding, possess computer vision features that can be leveraged for other applications, including colorimetric analysis.

Purpose of the Study:

• To develop and validate a novel method for quantifying free chlorine levels in water using colorimetric sensors integrated into back-compatible Color QR Codes.
• To assess the accuracy and reliability of this Color QR Code-based system under various real-world conditions, including different illumination and mobile device capture scenarios.
• To provide an accessible and practical solution for on-site water quality monitoring, particularly for the HORECA sector.

Main Methods:

• Development of custom Color QR Codes embedded with colorimetric references specific to two common free chlorine tests: Bromothymol Blue (BTB) strips and Diethyl-p-phenylenediamine (DPD) powder.
• Exposure of these Color QR Codes to various water samples with different free chlorine concentrations under diverse illumination conditions.
• Image capture of the colorimetric reactions using three different mobile devices for subsequent analysis and comparison with established measurement standards.

Main Results:

• The Color QR Code technology successfully digitized colorimetric readings for both BTB strip and DPD powder methods across different testing scenarios.
• The system achieved a notable accuracy of 88.10% for the BTB strip measurements and 84.62% for the DPD powder measurements.
• The proposed method demonstrated robustness and reliability when tested under various real-world conditions, including fluctuating illumination and diverse mobile device captures.

Conclusions:

• The integration of Color QR Codes offers a viable and accurate approach for the digital readout of colorimetric water quality tests, enhancing accessibility for on-site monitoring.
• This technology significantly improves the practicality of measuring free chlorine levels, overcoming the limitations of traditional methods that require specialized equipment.
• The developed system presents a promising advancement for ensuring drinking water safety, particularly within the hotel/restaurant/café (HORECA) sector, by enabling efficient and reliable water quality assessments.