Gas chromatography of 4,4'-diphenylmethane diisocyanate in the workplace atmosphere

A sensitive gas chromatographic procedure for the determination of 4,4'-diphenylmethane diisocyanate concentration in air is described. Traps containing 20-40-mesh silica gel coated with phosphoric acid are used. After the aspiration of the air, the silica gel is eluted with sodium hydroxide in methanol. The amine formed is then separated with a gas chromatograph and measured with a nitrogen-phosphorus detector. This can be performed in 7 min. Virtually no breakthrough occurs if an air concentration of up to 128 nmol in 20 l is sampled. The detection limit based on a 20-1 air sample is 0.7 microgram/m3. Complete analysis requires about 30 min. The method was used to determine the concentration of 4,4'-diphenylmethane diisocyanate in working environments during spraying operations.