A Novel Dry Sampler for Determination ofIsocyanates in Vapor Phase and Particulate Michael Ye, Jamie L. Brown, Olga I. Shimelis, Michael R. Halpenny, Daniel S. Vitkuske, Emily R. Barrey, and J. Patrick MyersSupelco, Div. of Sigma-AldrichBellefonte, PA 16823 USA
Daniel Karlsson, Marianne Dalene, and Gunnar SkarpingInstitutet För Kemisk Analys Norden AB, P.O. Box 461 281 24 Hässleholm, Sweden
Today the use of isocyanate monomers continues to increase with good reason. It’s estimated – 6 million tons of isocyanates produced globally with an annual growth rate of 10 to 15 percent.1 Products made with isocyanateshave excellent performance characteristics that we now expect from the products we purchase: excellent adhesion, hardness, gloss, flexibility, and the resistance to abrasion. Overexposure to isocyanates is a leading cause of “Workers Asthma”. Overexposure can also cause skin, eye, nose, and throat irritation. "On April 13, 2011, the EPA released action plans to address the potential health risks of methylene diphenyl diisocyanate (MDI) and related compounds."2
Supelco has partnered with Institutet för Kemisk Analys Norden AB (IFKAN)on a new active air sampling device for monitoring a broad range ofisocyanates monomers which can exist in both the gas and particle phase.
The Dry Sampler is an improvement to the impinger sampling technique that uses di-n-butylamine (DBA) as the derivitization reagent. The dry sampler is adopted as an international standard by the International Organization for Standardization (ISO 17734-1). The Dry Sampler is comprised of two parts, a denuder and a filter. The media inside the sampler is impregnated with a mixture of DBA and acetic acid. During sampling, the isocyanates react with the DBA to form stable isocyanatederivatives. The acetic acid creates an ion-pair with the DBA which reduces the volatility of the DBA.
Vapor phase isocyanates are collected in the denuder
The isocyanate particles are collected on the filter
Compared to the other derivatization agents used in other isocyanate samplers, DBA is the most volatile. This volatility is unique to the design of this new sampler. As the sampled air travels through the denuder fresh DBA is carried to the collection filter. This assures complete derivatization of the isocyanates -even if multiple layers of particles are collected on the filter. This also eliminates the risk of reagent depletion during sampling.
1. Place filter media from sampler in 15 mL centrifuge tube2. Add extraction solvents & deuterated internal standard3. Shake: 5 minutes, Sonicate:10 minutes, Re-shake: 20 minutes
Centrifuge: 10 minutes4. Remove (top) organic layer and place in a new tube5. Add fresh toluene to original sample6. Shake: 5 minutes, Sonicate: 10 minutes, Re-shake: 20 minutes
Centrifuge: 10 minutes7. Remove the new toluene and add it to the previous organic layer8. Organic layer is evaporated to complete dryness, then blown
down using: nitrogen evaporator or vacuum centrifuge9. Reconstitute with 1 mL of acetonitrile
Various types of shaking techniques were investigated. An orbital/vortex type shaker promoted both phases to intermix well and caused the filter media to shred into small pieces after shaking, assuring an efficient extraction.
Plastic vs. Glass Centrifuge Tubes for Sample Prep (contd.)
• We discovered some brands of plastic tubes did not behave like glass. As the molecular weight of the isocyanate-derivatives increased, the slopes of the calibration curve were different between some plastic tubes and glass tubes.
• Summary of the findings:• No interference background was found in any of the tubes we tested.• Some brands of plastic tubes became so distorted from the toluene extract
that it was difficult to get them in and out of the extraction equipment racks. • In reference to glass tubes - the septum of some brands of caps swelled,
with a noticeable color change in the extraction, We determined that caps with a PTFE face septum should be used.
Plastic vs. Glass Centrifuge Tubes for Sample Prep (contd.)
The evaporation step is done not only to concentrate isocyanate derivatives, but also to remove the excess DBA extracted from the sample media, thus making the final sample cleaner.We obtained good recoveries with both the nitrogen evaporator and the vacuum centrifuge.
The single MS method uses a longer column to create baseline separation of each deuterium labeled ISTD analytes from the eleven derivatives in the calibration standard.The gradient is slightly different for the MS method in which the starting conditions are the same, but the organic content is increased at a slower rate. This was necessary in order to separate the HDI-d9 (SIM = HDI-DBA + 18) peak from the ammonium adduct of the parent ion for HDI (HDI-DBA-NH4+).
Testing Filter Spikes• It's common for laboratories to conduct their own media spikes to determine extraction and desorption efficiencies. Experiments were conducted using neatisocyanates to spike the media. A 30 µg solution of neat 2,6-TDI was made in dry toluene. 0.002 mL of the solution was injected on the media in the denuder of the dry sampler, then capped and allowed to stand overnight. As a control, the same quantity of the 2,6-TDI was spiked into a vial containing 1.5 mol/L DBA-Acetic Acid in Methanol. The samples were then extracted and analyzed. The recovery from the spiked filter correlated well with the control.
2,6-Toluene diisocyanate (neat) spikes
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Control (1.5 mol/L DBA Solution) Dry Sampler Media Spike
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TDI C
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error bars = the concentration determined from the samples
Eleven isocyanates can be simultaneously sampled and analyzed making it possible to determine exposure concentrations for a broad range of isocyanatemonomers using a single sampler.A comprehensive extraction and analytical method has been developed that is robust and sensitive for the quantitation of isocyanates from air in single digit ppb levels. Research is currently underway to expand the use of the dry sampler for various isocyanate oligomers.
