Advances in Laboratory Sampling and Analysis

Advances in Laboratory Sampling and Analysis

Thursday, June 4, 2015, 9:00 AM - 12:20 PM

SR-128-01 Respirable​ Crystalline Silica Wipe Study

D. Johansen, B. Albrecht, OSHA, Sandy, UT

Objective: In the analysis of r​​espirable crystalline silica (RCS) it is important to ensure all analyte material is being effectively recovered. A common practice to transfer all RCS material from the sample cassette is to use the sample media to remove excess dust by wiping. This practice was evaluated to determine its effectiveness. 

Methods: Forty-nine field samples were prepared following OSHA ID-142 and wiped. The samples were then re-wiped in order to determine if any RCS remained on the sample after preparation. 

Results: The analysis of the samples determined quartz loadings on the filters ranged from 15 to over 900 μg. Effectiveness of the wiping procedure was addressed by comparing the results of the original samples to the second wipes. 

Conclusions: Current sample cassette wiping practices are adequate at the proposed and established target concentrations for RCS. 

SR-128-02 Possible Replacements for DM450 Filters in FTIR Analysis of Silica in Coal Mine Dust

D. Farcas, T. Lee, W. Chisholm, J. Soo, M. Harper, NIOSH, Morgantown, WV

Objective: To find a replacement filter for the vinyl/acrylic co-polymer filter (DM-450) that is currently used in US standard methods (MSHA) P-7 method and (NIOSH) Manual of Analytical Methods (NMAM) 7603 but which is no longer commercially available.

Methods: Nylon (47 mm, 0.45 µm pore size, HNWP04700, Millipore), polypropylene (PP, 47 mm, 0.45µm pore size, PP04547100, Sterlitech) and polyvinyl chloride (PVC, 47 mm, 5µm pore size, FPVC547, Zefon) filters were considered because the filters have high IR transmittance in the spectral region 600-1000 cm-1. Calibration curves using these filters were prepared according to the NMAM 7603 by pipet deposition of a suspension of standard reference material, respirable α-quartz (1878a), in isopropyl alcohol. Absorbance spectra of the quartz samples on the various filters were recorded and analyzed by the NMAM 7603 and MSHA P-7 methods. Limits of detection (LOD) and limits of quantification (LOQ) were determined from multiple measurements of blank filters. Coefficients of variation (CV) were determined from IR measurements of known masses (3 - 10 µg) of quartz for each filter. The filters were also tested to determine quartz masses in ashed coal dust samples by both methods. Pore size for each type of filter was determined by the bubble point test. Breakthrough of quartz particles for each filter was also investigated.

Results: LODs and LOQs from nylon filters determined according to MSHA P-7 were larger than those of PP and PVC. The values determined from the same spectra according to the NIOSH method were similar. The CV of the known masses of quartz samples were in the range of 1-18%. The nylon filter did not provide even particle deposition on filter possibly due to pressure drop across the filters when two different filters were superimposed during the redeposition procedure. A regression analysis of quartz masses determined by NIOSH and MSHA showed a relationship close to unity. Pore size measurements yielded values in close agreement with the manufacturers’ advertised pore sizes. No breakthrough of the quartz particles through any of the filters was observed.

Conclusions: The DM-450 filter specified by NIOSH and MSHA for quartz measurement in coal dust by FTIR can be replaced with PP and PVC filters without other modifications of their methods. The nylon filter is not as suitable due to uneven particle deposition.

SR-128-03 Interference Removal in Analysis of Respirable Crystalline Silica by Microwave Digestion

B. Albrecht, D. Johansen, OSHA, Sandy, UT

Objective: Kaolinite, a very commonly occurring mineral, interferes with the analysis of respirable crystalline silica (RCS) because some of its analytical diffraction lines overlap with those of quartz and cristobalite. A new closed vessel microwave technique to acid wash samples was developed to quickly digest the kaolinite while leaving polymorphs of RCS intact so they can be re-deposited for interference free analysis. This technique was tested to quantify its effectiveness.

Methods: Laboratory created samples containing target levels of RCS (40 μg of quartz and 40 μg of cristobalite) were spiked with maximum expected levels of interfering solids (2000 μg of kaolinite) to test the ability of a new closed vessel microwave acid digestion procedure to remove unwanted interferences and leave the RCS polymorphs of interest intact. Samples were analyzed by X-ray diffraction (XRD) both before and after the acid digestion.

Results: The microwave acid wash procedure enables the collection of much cleaner peak scans on useful analytical angles and recoveries suggest that RCS lost in the process is minimal. This is apparent in both the visual appearance of the peak scans and in the analytical recoveries obtained. Pre-acid wash recoveries for quartz on its analytical angles were primary through quaternary were 58.7, 39.7, 50.6, and 372 μg respectively. Post-acid wash results were much closer to theoretical 44.8, 42.5, 41.2, and 38.5 μg. Cristobalite data was similar: 52.4, 636.4, and 54.0 μg pre-wash and 38.2, 43.5, and 37.6 μg post-wash.

Conclusions: In some cases where interfering solid material makes the quantification of RCS difficult, improved results can quickly be obtained following a closed vessel microwave acid digestion procedure to remove unwanted solid material.

SR-128-04 Internal Cassette Deposits in Respirable Samplers

J. Soo, T. Lee, M. Kashon, M. Harper, NIOSH, Morgantown, WV

Objective: To compare quartz mass in coal dust deposited on internal surface of polystyrene and polypropylene (conductive) cassettes types for respirable size-selective samplers. 

Methods: Pittsburgh seam coal dust was aerosolized in a calm air chamber by using a fluidized bed aerosol generator without neutralization under the assumption that the procedure is similar to field sampling conditions. Four different respirable size-selective samplers (10-mm Dorr-Oliver nylon, SKC Aluminum, BGI4L, and GK2.69 cyclones) were employed with two different cassette types (polystyrene and polypropylene (conductive) cassettes). Two different levels of dust mass were tested with at least three repetitions for each level. The mass of coal dust was measured gravimetrically and quartz mass was determined by Fourier transform infrared spectroscopy according to NIOSH Manual of Analytical Method 7603. Coal dust deposited inside of the cassettes was wiped out with two or three successive PVC filters wetted with isopropyl alcohol until the surface of the cassettes was clean to visual inspection. 

Results: A total of 216 samples were collected. The mass fractions of the total quartz sample on the internal cassette surface are significantly different between polystyrene and polypropylene (conductive) cassettes for all cyclones (p<0.05). However, no consistent relationship between quartz mass on cassette internal surface and coal dust filter mass was observed. The BGI4L cyclone showed larger (but not significantly) and the GK2.69 cyclone showed significantly lower (p<0.05) internal surface deposit quartz mass fraction for polystyrene cassettes compared to other cyclones. 

Conclusions: This study confirms previous observations that the quartz residue on interior surface of polystyrene cassettes attached to cyclone pre-selectors can be a substantial part of the sample, and therefore need to be included in any analysis for accurate exposure assessment. On the other hand, the finding of the present study supports that the dust adhesion on interior wall of polypropylene (conductive) cassettes used with size-selective cyclones are negligible and that it is only necessary to analyze the filter catch.

CS-128-05 Dispelling the Myths: Understanding the Complexity of Isocyanate Sampling in the Workplace

D. LaGarde, OSHA, Sandy, UT

Situation/Problem: Workplace exposure to isocyanates is well-studied with established sampling and analytical protocols. Occupational sampling for isocyanates began over 50 years ago, yet research is ongoing and workers exposed to isocyanates continue to exhibit illness, why? Persons working in the same occupational environment exhibit different responses to isocyanate exposure, ranging from no response to potentially fatal hyper-sensitization. Exposures can be acute or chronic, where isocyanate concentrations can be very low for many hours or at a high concentration for just a few seconds. Routes of exposure may be inhalation and dermal. In addition, the measurement of isocyanates in an occupational environment is challenging to sample and analyze. Isocyanates can exist in the air as a vapor or as an aerosol with a wide range of particle sizes. Isocyanates are highly reactive and are comprised of numerous chemical species, monomers, pre-polymers, and polymers. Analytical standards are not available for many species. A number of “problems” are associated with current sampling methodology used for isocyanates including the mobility on a dry derivative filter, stability of the derivative prior to sampling, and under derivatization of large particles. Published research is often limited in scope; conclusions can be widespread, broadly interpreted, become myth, and then fact.

Resolution: Dispel myths that have evolved surrounding isocyanate exposure, sample collection, and analysis through research, education, and collaboration. Scientifically evaluate proposed improvements and empirical observations regarding occupational isocyanate exposure assessment and eliminate the myths that can lead to erroneous results and exposure conclusions.

Results: Comparisons performed to evaluate common issues associated with isocyanate sampling reveal the complexity of isocyanate sampling and analysis. The most accurate sampling and assessment for worker exposure comes from a thoughtful evaluation of the environment, isocyanates and co-reactants present, potential formation or breakdown products, and potential interferences using sampling protocols in established validated sampling and analytical methods.

Lessons Learned: Evaluate myths through the scientific method. Cause and effect, or empirical evidence, is not equal to scientific testing. Publications, advertisements, new sampler designs and processes do not supplant the tests completed to validate scientific methods used for chemical exposure quantification.

SR-128-06 Measurement of the Potential Exposure to Isocyanates Monomers and Oligomers during Spray Painting

J. Brown, E. Barrey, O. Shimelis, M. Halpenny, M. Ye, Sigma-Aldrich / Supelco, Bellefonte, PA

Objective: Monitoring of isocyanates in the workplace environment is important as these reactive compounds are capable of inducing respiratory disorders like “occupational asthma”. Airborne monomer and oligomer isocyanates can occur together in product formulations, such as automotive clear coat finishes. Analyzing the monomer and oligomer isocyanates in a single method provides the most efficient solution for determining the concentrations present during potential exposures.

Methods: In this field study, the sampling device used to collect the air samples incorporated a Dibutylamine impregnated media. The Dibutylamine derivatized the reactive isocyanates to form stable urea derivatives. This “dry” air sampler allowed sensitive and reliable detection of multiple isocyanates including monomers and oligomers. Low detection limits were obtained by using LC-MS-MS. Quantitative analysis of the isocyanates was possible by using the available deuterated internal standards.

Results: Both monomers and polymers of Isophorone diisocyanate (IPDI), and 1,6-Hexamethylene diisocyanate (HDI) were detected during this study. The quantitative results indicated that HDI-Isocyanurate and IPDI-Isocyanurate were present at the highest concentration inside the spraybooth during the spraying process. HDI polymeric species detected included; HDI-Isocyanurate, HDI-Uretidone and HDI-Biuret. The IPDI polymeric form IPDI-Isocyanurate was also present at higher concentrations than the monomer form.

Conclusions: The use of the dry sampling device allowed quantitative analysis and identification of the individual isocyanate species. The study indicated that isocyanate oligomers were present at much higher concentrations than the monomers during the spray painting process. 

CS-128-07 Isocyanate Field Extraction Procedure

J. Glowacki, University of Wisconsin – Madison, Madison, WI

Situation/Problem: Successful isocyanate sample collection depends upon sample derivatization at the time of collection. Derivatization occurs when the isocyanates come into physical contact with the derivatizing agent on the filter of the sampling media to form a stable by-product. 1-(2-pyridyl)piperazine is the derivatizing agent on the 37mm glass fiber filters referenced in OSHA 42 and 47 for the analysis of Diisocyanates. Isocyanate vapors and very fine aerosols are captured well using this method, as they react more completely on the filter to form the stable derivative. Larger aerosol droplets and high particulate air samples are problematic as their size impairs reaction with the derivatizing agent.

Resolution: To minimize the loss of unreacted aerosol or particulate isocyanate, the OSHA NEP now requires field extraction of isocyanate sample filters. The field extraction process will be clearly described, including detailed photographs. Rationale for recommended tools and PPE (personal protective equipment) will also be explained.

Results: Aerosol isocyanate samples that are field extracted will yield three or more times more analyte over non field extracted samples. Data showing the importance of isocyanate sample field extraction will be presented.

Lessons Learned: Collection recoveries can be significantly improved by field extracting aerosol and high particulate isocyanate samples. What can go wrong with the field extraction process? Real world samples present varied difficulties and challenges. Proper planning and understanding of the field extraction process can minimize these issues.

SR-128-08 Development and Validation of a New Personal Sampler for Monitoring Inorganic Acid Mist and Gases

C. Chien, L. Shou, C. Wu, University of Florida, Gainesville, FL; A. Theodore, Fracture, Gainesville, FL; Y. Hsu, Wood Buffalo Environmental Association, Fort McMurray, AB, Canada; B. Birky, Florida Industrial and Phosphate Research Institute, Bartow, FL

Objective: To develop a personal sampler to overcome the inaccurate measurement of inorganic acid mist and gases using NIOSH Method 7903.

Methods: To design a new sampler that consists of 3 components in an ergonomic smart phone shape to collect aerosol and gases separately: a parallel impactor for classifying acid mist following ACGIH/ISO/CEN defined human respirable/thoracic fraction, a porous membrane denuder for adsorbing acidic gases, and a filter pack to collect small particles penetrating the impactor and the denuder.

Results: Test results showed that the personal sampler maintained particle collection efficiency greater than 99% for 4-hour sampling time as well as 4-hour gas collection efficiency over 95% for SO2, HCl, and HNO3 with a feed concentration of 10, 10, and 4 ppm (two times of OSHA standards), respectively. Additionally, the sampler successfully separated the collection of SO2 from that of H2SO4, thus minimizing the interference when SO2 and H2SO4 coexist. Testing was also carried out according to OSHA’s Validation Guidelines for Air Sampling Methods Utilizing Chromatographic Analysis. Under both low (22%) and high (64%) relative humidities, the sampler’s analyte recovery was above 99%. While particle growth due to the hygroscopicity of sulfuric acid shifts particle collection toward the impactor at high RH, the mass concentration of sulfuric acid was conserved for the combined impactor and filter collection. The storage stability of the H2SO4 samples taken every 5 days showed that, for ambient storage, the overall standard error of the samples collected in 25 days was 5.76% with 95% confidence limit of 11.28%, while for refrigerated samples, the standard error was 4.96% and 95% confidence limit was 9.65%, indicating both storage methods impose no significant effect on the samples.

Conclusions: This validated new personal sampler will provide accurate and reliable monitoring of inorganic acid mist in occupational setting over conventional methods which suffer from interferences encountered when using current NIOSH method.

SR-128-09 Analytical Method Validation for the Use of Microfiber Cloth Swatches in Surface Wipe Sampling

M. Malinsky, B. Mader, 3M, St. Paul, MN

Objective: Wipe sampling of workplace surfaces is a valuable tool for dermal exposure assessments. The purpose of this investigation was to evaluate the use of microfiber cloth swatches, pre-wetted with solvent, as surface wipe media for acrylates. The microfiber cloth, which is designed for cleaning purposes, is physically more durable than other conventional wipe media.

Methods: Sampled wipes were solvent extracted and then analyzed using gas chromatography/mass spectrometry (GC/MS). The following quality control samples were prepared to evaluate the accuracy and precision of the analytical methodology: wipe spikes (extraction efficiency), surface spikes (sampling efficiency), blanks (media interferences), and holding time spikes (analyte stability on the wipe media).

Results: Wipe spikes produced recoveries within 100±25% demonstrating that the target analytes could be quantitatively extracted from the microfiber media. Wipes sampled from spiked aluminum foil demonstrated greater variability with recoveries between 100±50%. The acrylates tested for this study were stable on the wipe media for a minimum of fourteen days.

Conclusions: Microfiber wipes are a suitable media for surface wipe sampling for acrylates and potentially other classes of chemicals. The study demonstrated that quantitative results can be obtained for the analysis of the wipe samples. However the similarity of the transfer efficiency of the wipe sampling to actual dermal uptake could not be quantified.

SR-128-10 Sampling of Semi-Volatile Compounds - A New Sampling System for Simultaneous Sampling of Droplets and Vapors

D. Breuer, C. Friedrich, IFA- Institute for Occupational Safety and Health of the Germany Accident Insurance, Sankt Augustin, Germany; G. Dragan, 2Joint Mass Spectrometry Centre, Cooperation Group “Comprehensive Molecular Analytics”, Helmholtz Zentrum München, Neuherberg, Germany

Objective: The European Standard EN 13936 defines the basic requirements for semi-volatile compounds that can occur as vapor and particle at the same time at workplaces. Vapor and particles shall not be sampled separately and particles have to be sampled as inhalable fraction. Sampler containing filter and pumped sorbent tube in series are one of the suitable sampling trains. IFA has developed a sampling head (GGP-Mini) which is designed to sample the inhalable fraction at flow rates that can be easily combined with commercially available adsorption tubes. Particles will be sampled on a 13 mm filter. A basic set up with glass fiber filter and charcoal tube was tested.

Methods: Laboratory tests were performed with compounds in a boiling point range from 188 °C (propylene glycol) to 318 °C (n-octadecane). The substances were spiked directly on the filter and then air sucked through (0.33 l/min, 2 h). For further evaluation droplet/vapor mixtures of n-hexadecane, n-octadecane and diethylene glycol with droplet sizes between 1 µm and 4 µm were generated in a flow-tube reactor. All samples were analysed with GC-FID. In the flow-tube the aerosols were analysed online with a particle counter (particle number and concentration) and a flame ionisation detector (total concentration).

Results: Mainly substances with boiling points above 230°C up to 300°C were found on both substrates, filter and charcoal tube. For n-hexadecane with a droplet size of 2 µm the online measurements gives a result of 13 mg/m3 for the droplets and 24.2 mg/m3 for the overall concentration. The GGP-Mini showed different results for droplets (8.5 mg/m3) and vapor (16.7 mg/m3), the result for the sum of vapor and droplets (25.2 mg/m3) was in good agreement to the online measurement. Parallel sampling with charcoal tubes without upstream particle sampling showed differences arise as soon as droplets are the dominant component.

Conclusions: All tests have shown that the distribution between vapor and droplets is not constant, and that only the sum of vapor and droplets constitutes a reproducible result. The distribution is dependent upon numerous influencing factors including the concentration of the aerosol, the temperature, and, particularly in the case of polar substances, the atmospheric humidity.​