Simple Collection and 5-Minute UHPLC Assay for 11 Isocyanates

Isocyanates are highly reactive, low molecular weight chemicals. They are widely used in the manufacture of flexible and rigid foams, fibers, coatings such as paints and varnishes, and elastomers. Spray-on polyurethane products containing isocyanates have been developed for a wide range of retail, commercial, and industrial uses to protect cement, wood, fiberglass, steel, and aluminum, including protective coatings for truck beds, trailers, boats, foundations, and decks.

Isocyanates are powerful irritants to the mucous membranes of the eyes and gastrointestinal and respiratory tracts. Isocyanates can also sensitize workers, making them subject to severe asthma attacks if they are exposed again. Preventing exposure to isocyanates is a critical step in eliminating the health hazard. Engineering controls such as closed systems and ventilation should be the principal method for minimizing isocyanate exposure in the workplace. Other controls, such as worker isolation and personal protective clothing and equipment may also be necessary. Monitoring exposure is equally critical in the health and well-being of workers.

With that in mind, a simple collection tube for personal monitoring and associated analytical assay has been developed to support the industrial hygiene market. The ASSET™ EZ4-NCO Dry Sampler (Figure 1) for isocyanates is safe for the worker to use for personal sampling because it requires no field addition of reagents, no field extraction, and no special storage requirements. In addition, it is the only sampling device that achieves reliable low detection limits compared to existing commercially available devices. The ASSET EZ4-NCO sampling device is a unique dry sampler based on derivatization of isocyanate groups with di-n-butylamine (DBA). The sampler consists of a denuder and a filter, both impregnated with DBA. The extract is analyzed using LC–MS-MS offering the ultimate sensitivity and low detection limits not capable with other methods.

Figure 1: ASSET Isocyanate Field Sampler.

The design offers several advantages over existing devices such as:

• The ability to achieve low detection limits for both vapor and particulate phase isocyanates

• Sampling from 5 minutes > 8 hours

• Fast derivatization reactions into stable derivatives

• No storage limits before and after sampling

• High capacity

• No interferences

• No breakthrough

• No field extraction

Discussion

Figure 2 shows the chromatogram of a series of 11 common isocyanates. This isocyanate test mix is available as a standard, Cat. No. 40141-U. The gradient mobile phase employs LC–MS suitable solvents and buffers consisting of water, acetonitrile, and formic acid. All peaks are well, exhibiting baseline resolution. Peak shapes are symmetrical with minimal tailing. The 5 cm × 2.1 mm Titan™ UHPLC column. Cat. No. 577122-U, used in Figure 2 is a new offering from Supelco. Titan UHPLC columns are the outcome of the patent pending Ecoporous™ process, an economical route to UHPLC grade silica. The list price for this column is $399 USD. For further information on the ASSET field sampler, visit sigma-aldrich.com/asset. For further information on the Titan UHPLC, visit sigma-aldrich.com/titan.

Figure 2: 11 common isocyanates. Column: Titan C18, 5 cm × 2.1 mm, 1.9 µm (577122-U), mobile phase: (a) 0.05% formic acid in 5:95 acetonitrile:water; (b) 0.05% formic acid in 95:5 acetonitrile:water, flow rate: 0.5 mL/min, pressure: 270 bar, det.: MS, ESI (+), MRM, sample: isocyanates in acetonitrile, 0.06 µg/L, inj.: 2 µL. Peaks: 1. Isocyanic acid, 2. Methyl isocyanate, 3. Ethyl isocyanate, 4. Propyl isocyanate, 5. Phenyl isocyanate, 6. Hexamethylene diisocyanate, 7. 2,6-Toluene diisocyanate, 8. 2,4-Toluene diisocyanate, 9. Isophorone diisocyanate (isomer 1), 10. 4,4’-Methylenediphenyl diisocyanate, and 11. Isophorone diisocyanate (isomer 2).

ASSET, Ecoporous, and Titan are trademarks of Sigma-Aldrich Co LLC.

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Website: sigma-aldrich.com/analytical