A field method for determining 4,4′-di-isocyanatodiphenylmethane in air

Abstract

A method has been developed for determining up to 0·04 p.p.m. v/v of di-isocyanatodiphenylmethane (MDI) in a 5-litre sample of air. The test atmosphere is drawn through 0·4 M hydrochloric acid, which hydrolyses the isocyanate to the corresponding amine. This is then diazotised and coupled with 3-hydroxy-2-naphthanilide. After acidification of the solution the resulting pink compound is extracted into chloroform and compared visually with inorganic colour standard solutions. The preparation of three standards is described, corresponding to 0·01, 0·02, 0·04 p.p.m. of MDI, the recommended threshold limit value being 0·02 p.p.m. v/v. There is no interference from the tertiary-amine catalysts that are used with MDI in the production of polyurethanes.