Abstract:
Isocyanates are widely used as hardeners in tw-component paints and in the production of plyurethane materials. Commercially available isocyanates exist as monomers, dimers or polymers. Exposure to isocyanates can cause respiratory problems and can induce asthma-like symptoms in sensitized individuals at low exposure levels. OSHA has promulgated specific exposure limits for two mono0meric diisocyanates and NIOSH has recommended an exposure limit for total diisocyanates. There are currently no OSHA permissible exposure limits (PELs) or ACGIH threshold limit values (TIVs) for polymeric isocyanates.
Monitoring for isocyanates is conducted to evaluate worker exposure and compliance with permissible exposure limits. There are several commonly used sampling methods for determination of isocyanates in air including a NIOSH method and two OSHA methods. These methods were developed for specific isocyanate monomers such as toluene diisocyanate (TDI), methylene bisphenyl diisocyanate (MDI), and 1,6-hexamethylene dissocyanate (HDI). Samples are collected by drawing a known volume of air through filters coated with a derivatizing agent or through a bubbler containing a derivatixing agent in solvent. The derivatizing agent converts the unstable isocyanate into a stable urea derivative. Samples are extracted and then analyzed by high pressure liquid chromatography (HPLC).
The purpose of this study was to compare the relative sampling efficiencies of an impringer sampling technique to a coated filter sampling technigue for collecting both HDI monomer and polymers using 1-(2-pyridyl)piperazine as the deriviatizing agent. Two-component polyurethane paint spray aerosols were generated in a test chamber. A series of side bby side samplers using impregnated glass fiber filters and impwingers were placed on a rotating sampling table inside the exposure chamber. Total weight samples were collected to verify chamber aerosol uniformity. A Marple cascade impactor was used to determine particle size distribution of the paint spray aerosol. Filter and impinger samples were analyzed by high pressure liquid chromatography (HPLC) using UV detection at 254 nm. A diode array detector was used to identify and confirm the presence of isocyanates. Sample quantitation was performed using a monomeric standard curve.