Development of an optical formaldehyde sensor based on the use of immobilized pararosaniline

The colorimetric indicator pararosaniline has been immobilized onto the cation-exchange resins Amberlite IRC-50, Dowex 50W-X8 and cellulose phosphate by electrostatic bonding. The reflectance of each reagent phase was measured using a bifurcated fibre-optic system and a flow cell. Pararosaniline immobilized on cellulose phosphate was found to respond to formaldehyde without requiring the addition of sulfite to develop the purple chromogen. This immobilized system demonstrated a linear response to 50-2500 micrograms of formaldehyde and had a correlation coefficient of 0.9979. Acetaldehyde and butyraldehyde did not produce any interference. However, exposure to the unsaturated aldehydes, acrolein and crotonaldehyde, gave rise to responses that were much greater than that observed with formaldehyde.