The fluorimetric determination of methyl isocyanate in air is described. Me
thyl isocyanate in air was absorbed with dimethyl sulfoxide and hydrolyzed
to form methylamine. Methylamine was reacted with acetylacetone and formald
ehyde in pH 5.6 HOAc-NaOAc buffer solution to form N-methyl-2,6-dimethyl-3,
5-diacetyl-1,4-dihydropyridine, which is a fluorescent substance. The measu
rement of relative fluorescence intensity was carried out at 474 nm with ex
citation at 404 nm. Effects of pH, heating time and foreign ions on the det
ermination of methyl isocyanate were examined. The relationship between flu
orescence intensity and concentration of methyl isocyanate was linear in th
e range 0.00-0.80 mu g ml(-1). The linear regression equation was C = 0.001
I + 0.0092, with a linear regression correlation coefficient of 0.9994. Th
e recovery was 98.3-104.5% and the relative standard deviation was 1.5%. Th
e method is rapid, simple and highly sensitive, and can be used for the det
ermination of methyl isocyanate in air. The results obtained agreed with th
ose of an extraction-photometric method.