Sampling and Analysis of Isocyanates Used in Paints Robert P. Streicher National Institute for Occupational Safety and Health Publications of the U.S. Government are within the public domain and therefore are not copyrighted.

Background Isocyanate compounds are major components of spray paints used in the aerospace industry Paints contain primarily polyisocyanates with low levels of isocyanate monomer Primarily aliphatic isocyanates

Commonly Used Aliphatic Isocyanate Monomers

Polyisocyanate Species Found in Paints

Polyisocyanate Species Found in Paints (cont.)

Complications in Total Isocyanate Determination Vapor and Aerosol Very reactive (unstable) Potentially numerous species for which no analytical standards are available

Six Steps in Sampling and Analytical Methods Collection Derivatization Sample Preparation Separation Identification Quantification

Collection Efficiency Problems Aspiration efficiency Internal losses Transmission losses

Collection Particles – Inhalable Sampler (e.g., IOM): all particles – 37-mm filter: < 20  m – Impinger: 2  m < x < 20  m Vapor – may depend on derivatization

Overspray Aerosol Particle Size Rudzinski (1995):4.1 +/- 1.7  m 6.9 +/- 2.5  m Myer (1993):  m D’Arcy (1990):  m

Derivatization Capture (vapors on filters) Stabilization Detectability

Factors Affecting Derivatization Efficiency Inherent reagent reactivity Reagent concentration Reagent-isocyanate mixing

Impinger / Filter Comparisons Most field comparisons have found impingers to give higher results - Maitre (1996), Myer (1993), Czarnecki (1992) Rosenberg (1984) found filters to be higher Bello (2000) found IOM = impingers

Sampling Recommendations Be flexible Filter – Used for: - All particles < 2  m - Slow-cure particles > 2  m – Extract filters in the field – High-boiling solvent on filters (?) Impingers – Used for fast-cure particles > 2  m

Sample Preparation Extraction Sonication Filtration Solvent exchange Concentration Solid-phase extraction

Analytical Separation: Reversed-Phase HPLC

Analytical Strategies Bulk product for calibration (Bayer) Monomer for calibration (MAP Method, MDHS 25/2, NIOSH 5522)

Bulk Product for Calibration Less demanding HPLC and detection Requires that isocyanate composition of calibrant matches composition of exposure

Monomer Calibration Demanding HPLC and detection requirements Does not require bulk product calibrant with composition matching exposure Bulk product used qualitatively

HPLC: Isocratic or Gradient Elution?

Advantages of Isocratic Elution Simple Compatible with EC detector Stable baseline Unvarying response factor

Advantages of Gradient Elution Powerful - wider range of compounds Faster Better peak shape

HDI/IPDI Oligomer Bulk

Identification of Derivatized Isocyanates Monomers - Retention time Oligomers – Retention time – Two detectors - response ratio is diagnostic – Multi-dimensional detector (mass spectrometer, photodiode array)

Quantification Monomer and oligomer from monomer calibration curve

Conclusions Determination of isocyanates is complex Filter sampling of paints may be OK with short sampling times and field extraction Bulk product calibration or monomer calibration - choice depends on product variability, availability of product calibrants