Colorimetric monitoring of formaldehyde in indoor environment using built-in camera on mobile phone

A simple monitoring system of indoor air pollution is proposed by integrating a novel colorimetric detector of formaldehyde (HCHO) and a function of a built-in camera on mobile phone. The colorimetric detector employs a solid phase colorimetric reagent made from 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, ZnO, KIO4 and agar, and changes colour from white to purple by exposure to HCHO gas. The degree of colour changes expressed in Red, Green and Blue model model responded to the HCHO concentration levels both in air and from building materials. Limit of quantitation of the detector with 24 h-exposure resulted in 0.011 mg/m(3) of air concentration which meets a requirement of methodology to detect indoor air quality guideline level of HCHO set by World Health Organization. The detector is also applicable to classify HCHO-emitting materials at least into Type 1, whose emission flux is greater than 120 μg/m(2)/h, and others. Then, variation of the acquired photo images was investigated by using various mobile phones and changing conditions of photography. As a result, the calibration of the measured colour intensity with a colour standard reduced the variation of the results and gave a significant output when the auto-focused images were taken under the condition of common indoor environment.