This International Standard gives general guidance for the sampling and analysis of airborne organic
isocyanate (NCO) compounds in workplace air.
This International Standard is appropriate for a wide range of organic compounds containing
isocyanate functional groups, including isocyanate monomers and prepolymers. Examples of aromatic
monomers include toluene diisocyanate (TDI) (both 2,4- and 2,6-diisocyanatotoluene), naphthyl diisocyanate
(NDI) (1,5-diisocyanatonaphthalene) and methylenebis(4-phenylisocyanate) [MDI, systematically
named as di-(4-isocyanatophenyl)methane]. Examples of aliphatic monomers include isophorone
diisocyanate (IPDI, systematically named as 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane),
methylenebis(cyclohexylisocyanate) (hydrogenated MDI, HMDI) and 1,6-diisocyanatohexane (HDI) (also
known as 1,6-hexamethylenediisocyanate). Monomers containing a single isocyanate moiety (e.g. methyl
isocyanate, ethyl isocyanate, phenyl isocyanate, hexyl isocyanate) are produced during thermal degradation
of polyurethanes, i.e. flame bonding and laser cutting. Isocyanate polymers, also called polyisocyanates,
homopolymers, oligomers or prepolymers, are derived from the diisocyanate monomers by self-condensation
or reaction with polyols. Polymeric diisocyanates are widely used in the polyurethanes, paints and coatings,
and adhesives industries.
This International Standard is appropriate for measuring any product containing free isocyanate groups. It was
developed primarily for the commonly used MDI, HDI, and TDI, and their oligomers and polymers. It has
also been used for IPDI, HMDI, and NDI, and their oligomers and polymers. The exposure limit for
isocyanates in the UK requires measurement of total isocyanate groups, i.e. monomeric diisocyanates,
oligomeric, prepolymeric and polymeric diisocyanates and monoisocyanates. Because there are a wide range
of isocyanate structures and molecular masses, the chromatographic conditions used will need to be varied
according to the isocyanate formulation being determined. If both isocyanates and amines are believed to be
present, and both need to be determined, a standard which enables the simultaneous determination of both
amines and isocyanates may be more appropriate. This method has also been modified to allow
determination of mono-isocyanates produced during thermal degradation, the use of mass spectrometric
detection and other sampling equipment, e.g. 37 mm filters and other filter cassettes, but these
modifications are not covered in this International Standard. If a modified version of this method is being used,
it is the responsibility of the user to demonstrate that the modifications are valid.
The method is used to determine time-weighted average concentrations of organic isocyanates in workplace
atmospheres, and is suitable for sampling over periods in the range 0,5 min to 8 h. The method is designed
for personal monitoring, but can also be used for fixed location monitoring by suitable modification.
The method is suitable for the measurement of airborne organic isocyanates in the concentration range from
approximately 0,1 μg/m3 to 140 μg/m3 for a 15 l sample volume. The qualitative and quantitative detection
limits for isocyanate, defined as three times and 10 times the standard deviation of six blank determinations,
have been found to be typically between 0,001 μg and 0,004 μg of isocyanate per sample, respectively
(EC detection). For a 15 l air sample, these values correspond to qualitative and quantitative detection limits of
0,07 μg/m3 and 0,3 μg/m3, respectively.