National Institute for Occupational Safety and Health

“ Evaporate the acetylated sample to dryness under a gentle stream of nitrogen while warming to 60 °C on a hotplate. Redissolve the residue in 5.0 mL methanol, while agitating the sample in an ultrasonic water for 15 min.
CALIBRATION AND QUALITY CONTROL: 10.
11.
Prepare at least six working standards containing 0.01 to 4.0 μg/mL of the appropriate urea (s) (TDIU, HDIU, and/or MDIU) and 100 μg/mL of 1- (2-methoxyphenyl) piperazine by adding aliquots of calibration stock solutions to 2 mL methanol in a 10-mL volumetric flask. Add 10 μL acetic anhydride to each standard. ”

“ Connect the assembled impinger to a sampling pump. Sample 5 to 500 L of air at 1.0 L/min. NOTE 1: Toluene evaporates during sampling; when level of solution drops below 10 mL, restore volume to 15 mL with toluene. NOTE 2: The reagent in the sampling medium reacts with isocyanates to form ureas: CH3OC6H4NC4H8NH + R-N=C=O → CH3OC6H4NC4H8NC (=O) NHR Prepare blank samples by transferring 15 mL sampling medium to 20-mL vials. Transfer the sample solution to a 20-mL vial for shipment. Rinse both impinger parts with 2 to 3 mL toluene and add rinsings to the sample. ”

“ Mix and dilute to the mark with methanol. NOTE: The standard solutions need include only ureas derived from the diisocyanates expected in the air samples. Analyze working standards together with samples and blanks (steps 13 through 15) . ”