Occupational exposure to diisocyanates is well documented as a cause of respiratory sensitization and occupational asthma. Hexamethylene diisocyanate (HDI) is a commonly used diisocyanate in the surface coating industry. The focus of research in the past has been on the inhalation hazards associated with the use of HDI. However, inhalation exposure may account for only part of the total body dose resulting from exposure in occupational settings. Recent animal studies have suggested a link between dermal exposure to diisocyanates and respiratory sensitization, but dermal exposure assessment methods and techniques for these compounds have been slow to emerge.

An analytical method using liquid chromatography-mass spectrometry (LC-MS) was developed to detect and quantify dermal exposure to HDI. NIOSH Method 5521: “Isocyanates, Monomeric”, originally developed for air samples, was modified for use with our non-invasive dermal tape-stripping technique. HDI was detected as the urea derivative by monitoring its protonated molecular ion at m/z 553.7. An octamethylene diisocyanate (ODI) urea derivative (1000 pmol spike) was used as an internal standard for all samples, and was detected using the protonated molecular ion at m/z 581.7. A standard curve developed with pure HDI urea derivative and spiked with 1000 pmol of the internal standard was used to evaluate sample results. Evaluation of the method included storage stability and extraction efficiency tests.

To evaluate sample stability during storage, tape strips (in triplicate) were spiked with a known amount of HDI-containing paint and held in a toluene/1-(2-methoxyphenyl)-piperazine solution at 4°C for a period of time ranging from 1 to 13 days. Samples were acetylated, evaporated, and redissolved in methanol before analysis by LC-MS. Results were evaluated using a standard curve prepared on each day of analysis.

Extraction efficiency of the method was also investigated. Tape strips (in triplicate) were spiked with known amounts of base paint and pure liquid HDI, and held overnight in a toluene/1-(2-methoxyphenyl)-piperazine solution at 4°C. The extraction efficiency was evaluated for eight different amounts of pure HDI, ranging from <10 pmol to 1000 pmol. Samples were analyzed by LC-MS on the next day and the results evaluated using a standard curve.

The method will be evaluated in upcoming field studies of industrial spray-painting operations.