Fiberoptic colorimetric sensor for in situ measurements of airborne formaldehyde in workplace environments

Abstract

Formaldehyde (FA) involvement in specific economic activities has become one of the major threats for their worker’s health. The risks of exposure to FA include carcinogenic effects and important respiratory affections. One of the essential requirements to ensure safe working conditions is the availability of reliable FA monitoring systems. In this work we have developed a semi-continuous integrating optical sensor based on the evanescent field absorption of light by the FA-sensitive cladding of a plastic optical fiber. To this aim, we capitalized on the acid catalyzed FA-Leuco Fuchsin (LF) colorimetric reaction. We have also substantially reduced the costs of the typical fiber optic sensors by using poly(methyl methacrylate) 3D printing filaments as optical waveguides for the first time. The filaments are coated with a LF-doped Nafion® perfluorosulfonated cladding. The FA sensing fibers are interrogated with a custom-built optoelectronic device using dedicated software, tailored to in situ, online unattended atmospheric FA monitoring. Limits of detection from 0.03 to 0.20 ppmv (0.037–0.25 mg m⁻³) for 67–33% relative humidity, respectively, have been achieved for a 15 min sampling time that matches the legal requirements for the FA short term exposure limits, with automatic analyte level-dependent regeneration time. The sensor responds at least up to 5.5 ppmv (6.77 mg m⁻³). The portable prototype has been tested for 4 months at the paper impregnation process unit of a Spanish industry.