A field method for the determination of organic aromatic isocyanates in air

A general field method is described for the determination in air of some organic aromatic isocyanates commonly used in industry. Collection of the isocyanate vapour or aerosol, or both, is effected in a mixture of hydrochloric acid and dimethylformamide. The amine produced is diazotised and coupled with N-1-naphthylethylenediamine to form a coloured complex, the intensity of which is compared with a set of permanent colour standards appropriate to the isocyanate being determined. The method enables the determination of up to 0·04 p.p.m. v/v of isocyanate in air to be made. The procedure is simple and the time required for a complete analysis is about 35 minutes.