Rosa Key-Schwartz

Determination of Airborne Isocyanate Exposure: Considerations in Method Selection

To assess worker isocyanate exposures in a variety of processes involving the manufacture and use of surface coatings, polyurethane foams, adhesives, resins, elastomers, binders, and sealants, it is important to be able to measure airborne reactive isocyanate-containing compounds. Choosing the correct methodology can be difficult. Isocyanate species, including monomers, prepolymers, oligomers, and polyisocyanates, are capable of producing irritation to the skin, eyes, mucous membranes, and respiratory tract. The most common adverse health effect is respiratory sensitization, and to a lesser extent dermal sensitization and hypersensitivity pneumonitis. Furthermore, isocyanate species formed during polyurethane production or thermal degradation may also produce adverse health effects. Isocyanate measurement is complicated by the fact that isocyanates may be in the form of vapors or aerosols of various particle size; the species of interest are reactive and therefore unstable; few pure analytical standards exist; and high analytical sensitivity is needed. There are numerous points in the sampling and analytical procedures at which errors can be introduced. The factors to be considered for selecting the most appropriate methodology for a given workplace include collection, derivatization, sample preparation, separation, identification, and quantification. This article discusses these factors in detail and presents a summary of method selection criteria based on the isocyanate species, its physical state, particle size, cure rate, and other factors.

An Evaluation of Aerosol- and Liquid-Generated Silica Samples for Proficiency Analytical Testing

SRI International has prepared dynamically generated silica samples since 1980 for the National Institute of Occupational Safety and Health (NIOSH) and the American Industrial Hygiene Association (AIHA) Proficiency Analytical Testing (PAT) programs. Aerosol-generated samples were developed in 1980 to more closely approximate real world samples and to improve intrabatch precision. Liquid-generated samples may provide tighter control limits, and this method has been reexamined as the generation procedure of choice. Sample preparation procedures have also been investigated to minimize analytical uncertainty and, hence, obtain a true evaluation of the sampling error. Samples were analyzed by SRI, NIOSH, and the Wisconsin Occupational Health Laboratory, using X-ray diffraction or Fourier transform infrared spectrometry (FTIR). Results were plotted and statistically evaluated, then compared to the existing PAT interlaboratory database.

Comparison of Sampling Methods for Monomer and Polyisocyanates of 1,6-Hexamethylene Diisocyanate During Spray Finishing Operations

A comparison study of isocyanate sampling methods for 1,6-hexamethylene diisocyanate (HDI) monomer and HDI-based polyisocyanates was conducted in spray painting environments. This study compared the performance of the Iso-chek sampler against existing and proposed National Institute of Occupational Safety and Health (NIOSH) and Occupational Safety and Health Administration (OSHA) monitoring methods for HDI-based isocyanates. Six methods for monitoring HDI monomer and polyisocyanate levels were compared. Fifty-eight sampling sets were collected during spray painting of aircraft and aircraft parts at four U.S. Air Force bases. Impinger and cassette samplers were mounted side-by-side on a mannequin located in paint overspray areas. For HDI monomer sampling results, there were no significant differences between NIOSH 5521, NIOSH 5522, OSHA 42, MAP (the proposed NIOSH method), and the Iso-Chek. For HDI-based polyisocyanates, NIOSH 5522, NIOSH 5521, Iso-Chek, and the Total Aerosol Mass Method (TAMM) were significantly different from one another. There was no significant difference between MAP and the NIOSH 5522 polyisocyanate sampling results. This study suggests the Iso-Chek and MAP sampling methods compare favorably with established methods for monitoring in HDI spray painting environments and the Total Aerosol Mass Method provides a reasonable upper boundary for estimating HDI polyisocyanate concentrations. The results also reemphasize aerosol sampling physics and sampler geometries must be carefully considered and appropriate samplers used when measuring exposures in spray paint environments where particulates are of the inhalable size.

Proficiency Analytical Testing (PAT) Silica Variability, 1990–1998

Industrial hygiene laboratories use one of three analytical techniques (X-ray diffraction spectrometry, infrared absorption spectrometry, and colorimetric spectrophotometry) for the quantitative determination of crystalline silica. Interlaboratory variability historically has been high for these analyses (∼25–35% relative standard deviation). Agreement between laboratories, as measured by the American Industrial Hygiene Association Proficiency Analytical Testing program over the period April 1990 through April 1998, was studied. Analysis of over 11,000 data points (laboratory/sample/round combinations) showed some significant differences between analytical methods in their relative recovery and precision, although overall mean recoveries were similar for the three techniques. Relative recovery of colorimetric results (but not those of the X-ray or infrared results) was significantly affected by sample loading in the range 40–170 µg silica per sample. Differences on the order of 5–10% were produced in some...

Analytical problems encountered with NIOSH method 5521 for total isocyanates

A recent analysis for total isocyanates in air using National Institute for Occupational Safety and Health Method 5521 presented difficulties in the identification of an oligomeric isocyanate species. Two problems were encountered during the analysis. A false negative response in the high performance liquid chromatography chromatogram was encountered in a majority of the field samples. An anomalous peak served to give a false positive in some of the field blanks and in some of the field samples. Through supplementing the ratio criterion of Method 5521 using the complete UV absorption spectrum from a photodiode array (PDA) UV detector, the two peaks were successfully identified. However, this need for additional data to identify an oligomeric isocyanate species raises the question of whether the ratio criterion of Method 5521 allows the qualitative identification of isocyanate oligomers.

A Comparison of Solid Sampler Methods for the Determination of Hexamethylene-Based Isocyanates in Spray-Painting Operations

A polyurethane foam sponge impregnated with 1-(2-methoxyphenyl) piperazine in dimethylsulfoxide was mounted in both cassette and inhalable organic monitor samplers and these were then compared with a dual-filter cassette. The samplers were used for the collection of hexamethylene diisocyanate (HDI) monomer and oligomers during actual spray-painting operations. The dual filter cassettes were positioned on a mannequin. The polyurethane foam cassette (PUF CAS) and polyurethane foam inhalable organic monitor (PUF IOM) samplers were positioned on a cart in the same maximum overspray area. Data from this pilot study suggest that there is no significant difference (P < 0.05, n = 6) in the amount of HDI monomer obtained with the PUF IOM sampler when compared with the amount obtained from the dual filter cassette. The data also suggest that the PUF IOM sampler yields a higher amount of HDI oligomer than either the dual filter cassette or the PUF CAS sampler, neither of which exhibited a significant difference (P < 0.05, n = 6) from each other.

An Approach to Area Sampling and Analysis for Total Isocyanates in Workplace Air

An approach to sampling and analysis for total isocyanates (monomer plus any associated oligomers of a given isocyanate) in workplace air has been developed and evaluated. Based on a method developed by the Occupational Health Laboratory, Ontario Ministry of Labour, Ontario, Canada, isocyanates present in air are derivatized with a fluorescent reagent, tryptamine, in an impinger and subsequently analyzed via high-performance liquid chromatography (HPLC) with fluorescence detection. Excitation and emission wavelengths are set at 275 and 320 nm, respectively. A modification to the Ontario method was made in the replacement of the recommended impinger solvents (acetonitrile and 2,2,4-trimethylpentane) with dimethyl sulfoxide (DMSO). DMSO has the advantages of being compatible with reversedphase HPLC and not evaporating during sampling, as do the more volatile solvents used in the Ontario method. DMSO also may dissolve aerosol particles more efficiently during sampling than relatively nonpolar solvents. Several formulations containing diisocyanate prepolymers have been tested with this method in the laboratory. This method has been issued as National Institute for Occupational Safety and Health (NIOSH) Method 5522 in the first supplement to the fourth edition of the NIOSH Manual of Analytical Methods. This method is recommended for area sampling only due to possible hazards from contact with DMSO solutions containing isocyanate derivatives. The limits of detection are 0.1 microgram/sample for 2,4-toluene diisocyanate, 0.2 microgram/sample for 2,6-toluene diisocyanate, 0.3 microgram/sample for methylene bisphenyl diisocyanate, and 0.2 microgram/sample for 1,6-hexamethylene diisocyanate.

Evaluation of tryptamine in an impinger and on XAD-2 for the determination of hexamethylene-based isocyanates in spray-painting operations.

Tryptamine was evaluated as a reagent for derivatizing hexamethylene diisocyanate (HDI) monomer and oligomers during actual spray-painting operations. In one side-by-side sampling study, an impinger filled with 1-(2-methoxyphenyl)piperazine in toluene was compared with a second impinger filled with tryptamine in dimethyl sulfoxide (DMSO). The amount of HDI monomer obtained was below the limit of quantification for both impingers. The amount of HDI oligomer obtained when using 1-(2-methoxyphenyl)piperazine in toluene was comparable to the amount obtained when using an impinger filled with tryptamine in DMSO. In a second side-by-side sampling study, a tryptamine-coated XAD-2 resin was used as a sorbent. The relative collection efficiency of the tryptamine-coated XAD-2 resin was on average 60% of the value obtained using an impinger filled with tryptamine in DMSO. The results indicate that using an impinger filled with tryptamine in DMSO gives higher concentrations of isocyanate than a tryptamine-coated XAD-2 sorbent for HDI monomer and oligomer.

Consideration of Kaolinite Interference Correction for Quartz Measurements in Coal Mine Dust

Kaolinite interferes with the infrared analysis of quartz. Improper correction can cause over- or underestimation of silica concentration. The standard sampling method for quartz in coal mine dust is size selective, and, since infrared spectrometry is sensitive to particle size, it is intuitively better to use the same size fractions for quantification of quartz and kaolinite. Standard infrared spectrometric methods for quartz measurement in coal mine dust correct interference from the kaolinite, but they do not specify a particle size for the material used for correction. This study compares calibration curves using as-received and respirable size fractions of nine different examples of kaolinite in the different correction methods from the National Institute for Occupational Safety and Health Manual of Analytical Methods (NMAM) 7603 and the Mine Safety and Health Administration (MSHA) P-7. Four kaolinites showed significant differences between calibration curves with as-received and respirable size fractions for NMAM 7603 and seven for MSHA P-7. The quartz mass measured in 48 samples spiked with respirable fraction silica and kaolinite ranged between 0.28 and 23% (NMAM 7603) and 0.18 and 26% (MSHA P-7) of the expected applied mass when the kaolinite interference was corrected with respirable size fraction kaolinite. This is termed “deviation,” not bias, because the applied mass is also subject to unknown variance. Generally, the deviations in the spiked samples are larger when corrected with the as-received size fraction of kaolinite than with the respirable size fraction. Results indicate that if a kaolinite correction with reference material of respirable size fraction is applied in current standard methods for quartz measurement in coal mine dust, the quartz result would be somewhat closer to the true exposure, although the actual mass difference would be small. Most kinds of kaolinite can be used for laboratory calibration, but preferably, the size fraction should be the same as the coal dust being collected.