Abstract
Exposure to colorless ammonia vapor could result in failure of human organs or even death. Thus, it is of great significance to build up a portable quick onsite recognition technique for ammonia vapor. In this context, we report the preparation of highly sensitive, reversible, portable, fast detection time, cost effective solid state microporous cellulose test strips that exhibit a naked-eye colorimetric responsiveness within a fraction of second to ammonia vapor. An easy-to-prepare pH- responsive tricyanofuran-hydrazone (TCFH) dye was developed. The hydrazone recognition unit is able to selectively monitor ammonia over a series of other alkaline organic compounds and solvents. This TCFH was diffused in-situ within the as-prepared microporous cellulose acetate (CA). The size, sensitivity, and subsecond response of this spectroscopic hydrazone probe made them suitable for inclusion into cellulose acetate strips sensor assays (CA-TCFH) and ammonia vapor detection. The aqueous ammonia concentration range between 0.4 and 72 ppb displayed a color shift of the spectroscopic hydrazone dye from yellow to purple. The color shift of CA-TCFH was monitored from yellow to orange, red and purple with increasing the aqueous ammonia concentration, which was studied by color strength and CIE Lab measurements. Cellulose acetate test strip displayed a good detection limit as low as 0.4 ppb of aqueous ammonia. When cellulose sensor strip is subjected to ammonia vapor, the conversion of spectroscopic hydrazone probe into the hydrazone anion form causes a rapid color change. The microporous cellulose acetate showed high porosity with a pore diameter in the range of 4.5-7.5 mu m.