DEVELOPMENT OF A MONITORING TAPE FOR THE DETERMINATION OF FORMALDEHYDE GAS IN FUMIGATION

A porous cellulose tape impregnated with a coloring solution which includes hydroxylamine sulfate, netanil yellow (pH indicator; pH 1.2-2.3, red double-line arrow pointing left and right yellow), glycerin and methanol is a sensitive means of detecting formaldehyde gas. The formaldehyde reacts with hydroxylamine sulfate to produce sulfuric acid. When the sample including formaldehyde was passed through the tape, the color of the tape changed from yellow to red. The degree of color change was proportional to the concentration of formaldehyde at constant sampling time and flow rate. The degree of color change could be recorded by measuring the intensity of reflecting light (555 nm). No interference was observed from methanol (1 vol %), isopropanol (1 vol %), carbon dioxide (4.9 vol %), hydrogen (50 vol %), nitrogen dioxide (105 ppm), ammonia (246 ppm), nitrogen monoxide (105 ppm), hydrogen sulfide (52 ppm) or hydrogen fluoride (6 ppm). The selectivity coefficients for gases relative to formaldehyde were 1/3 for acetaldehyde and 1/25 for acetone. The response of formaldehyde was influenced by moisture in sample gas. The detection range was 100-3000 ppm for formaldehyde at a sampling time of 40 s and a flow rate of 400 ml/min.