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[1]. 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[2]. This method has also been modified to allow determination of mono-isocyanates produced during thermal degradation[3], the use of mass spectrometric detection[4] and other sampling equipment, e.g. 37mm 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 0,5min to 8h. The method is designed for personal monitoring, but can also be used for fixed location monitoring by suitable modification.
NOTE The objective of air monitoring is usually to determine worker exposure and, therefore, the procedures described in this method are for personal sampling in the breathing zone. The method can be used for background or fixed location sampling. However, it should be recognised that, due to aerodynamic effects, samplers designed for personal sampling do not necessarily exhibit the same collection characteristics when used for other purposes.
The method is suitable for the measurement of airborne organic isocyanates in the concentration range from approximately 0,1µg/m3 to 140µg/m3 for a 15l 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 0,001µg and 0,004µg of isocyanate per sample, respectively (EC detection). For a 15l air sample, these values correspond to qualitative and quantitative detection limits of 0,07µg/m3 and 0,3µg/m3, respectively.