D. Deininger, D. Routkevitch, C. Kostelecky, Synkera Technologies Inc., Longmont, CO.
The accurate and reliable measurement of toxic and flammable gases is an area of great concern in many applications related to industrial health and safety. The development of new and improved sensor technologies is an area of active research. This paper presents the results obtained to date on the development of a new ceramic micromachined sensor platform. This sensor platform is built from anodic alumina, a material that features highly uniform nanopores with dimensions on the order of 5 to 300 nm. Hybrid micromachining techniques are used to create a wide variety of 3-D ceramic structures applicable to sensing, including microhotplates of various designs as well as thin supported membranes for acoustic sensor measurements. This new sensor platform can be tailored for the detection of a wide range of analytes, using sensing principles including conductometric measurements, catalytic combustion measurements, and acoustic measurements. It takes advantage of the high surface area of anodic alumina, is rugged and reliable, and is very affordable. The resulting microsensor enables smaller personal monitors and lower power consumption than conventional sensors. The fast thermal response enables advanced temperature modulation modes of operation. This presentation will describe the development and testing of sensors based on this platform for the detection of a wide range of toxic and flammable gases.
P. Juan, S. Tsai, National Taiwan University, Taipei, Taiwan.
Fungus is an important indoor air pollutant and is known to be a fundamental allergen of asthma. Air sampling methods for bio-aerosols are often performed for the sampling of fungi but can be applied only when the spores are present in the air. On the other hand, microbial volatile organic compounds (MVOCs), which are the metabolites of fungi, can also be determined to relate the presence of fungi even when there is no spore available. Therefore a rapid, cost-effective, and accurate sampling system for exposure assessment of MVOCs would be of extreme benefit to improve the quality of indoor air. The aim of this research focused on the developing of sampling and analysis technique for indoor MVOCs. A solid-phase microextraction (SPME) technique was used as a diffusive sampler; its performances were validated on major indoor MVOCs, including 1-butanol, 1-octen-3-ol, 2-methyl-1-butanol, 2-heptanone, 2-pentylfuran, 2-hexanone, 3-octanone, 3-methyl-1-propanol, and methyl benzoate. Carbowax/divinylbenzene stableflex 70-μm fiber was selected because it provided the best adsorption capacity. Known concentrations of MVOCs were generated in gas bags for the validations of SPME diffusive samplers. After sampling, the sampler was inserted into the injection port of a portable gas chromatograph with flame ionization detector (portable GC-FID) for thermal desorption and analysis. The desorption efficiency was 100% when the time for thermal desorption was 1.5 min. The experimental sampling rates were (7.93±1.00)×10-5 for 2-methyl-1-butanol; (7.80±0.60) ×10-5 for 1-butanol; (4.22±2.17)×10-5 for 1-octen-3-ol; (6.54±0.30)×10-5 for 2-heptanone; (7.85±0.37)×10-5 for 2-pentylfuran; (5.86±0.26)×10-5 for 2-hexanone; (2.37±0.35)×10-4 for 3-methyl-1-propanol; (9.14±0.41)×10-5 for 3-octanone; and (4.23±1.04)×10-5 cm3/sec for methyl benzoate. The designed diffusive sampling device for MVOCs has both the advantages of passive sampling and SPME technique. Compared with other methods, the current designed sampler provides a convenient and sensitive tool for the exposure assessments of indoor MVOCs.
I. Lee, S. Tsai, National Taiwan University, Taipei, Taiwan.
Ozone is one of the major air pollutants to which exposure might cause severe health effects, such as coughs, asthma, headaches, and lung diseases. For the assessments of ozone exposures, several personal passive samplers are currently available. However, solvent desorptions are commonly needed for the techniques, which makes the methods inconvenient. On the other hand, solid-phase microextraction (SPME) presents many advantages over conventional analytical methods by combining sampling, preconcentration, and direct transfer of the analytes into a standard gas chromatography (GC) system. Therefore, the purpose of this research was to develop a passive sampler for ozone based on SPME. Known concentrations of ozone were generated by the calibrated ozone generator in an exposure chamber. The poly(dimethylsiloxane)/divinylbenzene (PDBM/DVB) fiber was selected and 1,2-Di-(4-pyridyl)ethylene (DPE) was first loaded unto the fiber. After exposures of ozone, pyriden-4-aldehyde was formed on the fiber and further headspace extraction of O-(2,3,4,5,6-Pentafluorobenzyl)-hydroxylamine hydrochloride (PFBHA) of the fiber was followed. The reactants, oximes, were then determined by gas chromatography-mass spectrometry (GC-MS) by directly inserting the SPME fibers into the injection port for thermal desorption and analysis. The desorption efficiency was found to be 100% when the time for thermal desorption was 2 min. The experimental sampling constant of the designed passive sampler as well as the effects of different environmental factors on the samplers were also validated.
C. Lungu, S. Crawford, D. Bocard, University of Alabama at Birmingham, Birmingham, AL.
Thermoset composite materials offer high strength and light weight. They are being tested as alternatives to metal in military, civil, and commercial applications including transit, construction, and recreational uses. Composite materials are used in many consumer applications such as furniture, shower units, ceiling and wall panels, institutional seating, and toys and games. Exposure to styrene, one of the main components of thermoset composite materials, raises some health concerns; it is listed by the International Agency for Research on Cancer as a possible human carcinogen (Group 2B). To estimate exposure to styrene emitted from resin-containing composite materials, emission tests were conducted in the laboratory. Kevlar fiber (KF) vinyl ester resin samples, fabricated 2.5 yr previous to testing, were placed inside a temperature controlled small environmental test chamber. Compressed air was passed successively through a charcoal column, a desiccant column, and a high-efficiency particulate air (HEPA) filter to obtain a clean, dry airflow. A mass flow controller was used to maintain a constant airflow through the chamber. The 0.92 L/min airflow resulted in about one air change per hour in the 55-L stainless steel chamber. The 24.1 x 15.24 x 0.3 cm KF samples were placed one at a time vertically in the chamber, and the concentration in the chamber was periodically monitored using an infrared spectrometer (MIRAN). Emission tests were conducted at 23ºC and 35ºC. Monitoring was conducted for two days for each sample, and the total emitted amount of styrene and the emission rate were determined. The total styrene amount emitted during 45 hr was 0.084 mg at 35ºC and 0.049 mg at 23ºC. The highest concentration in the chamber was 40 mg/cm3 at the highest temperature and 23.7 mg/m3 at the lowest temperature. The average emission rate was determined to be 0.113 mg/cm2 at 35ºC and 0.067 mg/cm2 at 23ºC.
P. Sacco, E. Grignani, D. Pagani, F. Quaglio, L. Zaratin, Fondazione Salvatore Maugeri-Centro di Ricerche Ambientali, Padova, Italy.
The International Agency for Research on Cancer classifies 1,3-butadiene as probably carcinogenic for humans (Group 2A), and isoprene is classified as possibly carcinogenic for humans (Group 2B). Both compounds are widely used in the production of elastomers. Therefore, analytical methods capable of measuring such compounds at the ppb level, well below the threshold limit values (TLVs) set for workplace air, will be valuable tools for industrial hygienists. A number of methods allow the measurement of 1,3-butadiene in workplace air by pumping air through activated charcoal or molecular sieves, followed by solvent or thermal desorption and gas chromatography. More recently, methods were proposed based on diffusive sampling onto molecular sieves or graphitized carbon blacks. However, the sampling rates of such methods, based on axial diffusion tubes, are lower than 1 ml/min and do not allow ppb level sensitivities. In this work, a method for measuring 1,3-butadiene and isoprene is presented, based on radial diffusive sampling, thermal desorption, and gas chromatography. Two sets of standard atmosphere experiments were carried out to assess the performance of radial diffusive samplers, filled with graphitized carbon black, for sampling 1,3-butadiene or isoprene, separately. A dynamic exposure chamber with one to three gaseous dilution steps was used. The testing conditions were set at 20°C and 50% relative humidity, 8-hr exposure time and concentration levels from the TLV (2 ppm) down to a few ppb. The diffusive sampling rates for 8-hr exposure were in the range of 30-40 ml/min. Minimum quantifiable concentrations are as low as 1 ppb or better. High diffusive sampling rates, combined with enhanced sensitivity offered by thermal desorption, give the method the capability of measuring low concentrations of compounds suspected of carcinogenic properties. The use of diffusive sampling allows industrial hygienists to overcome explosive hazards when sampling in chemical plants or other restricted working environments.
D. Cardin, C. Casteel, T. Robinson, Entech Instruments Inc., Simi Valley, CA.
Personal monitoring is typically performed in the workplace using either badge or adsorbent cartridge samplers. Adsorbent cartridges (traps) provide better accuracy than badge samplers but are less convenient and more cumbersome, due to the size and weight of required pumps and batteries. Results from badge samplers can vary as much as twofold to fivefold based on the total air movement over the badge during sampling. An alternative diffusive sampling device is introduced that uses a principle called “helium diffusion exchange sampling” to provide consistent sampling into a 40-mL vial worn in the breathing zone. A deactivated vial containing helium is positioned using a small Velcro pouch, with sample collection commencing with the insertion of a sampling needle through a septum port. As helium starts to diffuse out through the needle, a vacuum forms within the vial, causing air to move countercurrent to the helium and thereby reducing the rate of helium elimination. As air starts to mix within the vial, the vacuum forms more slowly, reducing the rate of countercurrent dilution of the helium. The net result is that the concentration of air and helium in the tube remains relatively constant during the first 50% exchange of the vial. This results in a nearly constant sampling rate. By choosing the appropriate length and diameter of the needle, the sampling time can be tailored to allow an 8-hr passive sample collection. The device is much less susceptible to errors from air movement over the sampler, due to the small ratio of the inlet tube’s diameter relative to its length. The sampler is designed to be disposable, with a special leak-tight cap that prevents any more exchange after sampling is terminated. Data will be presented showing the reproducibility of this technique as well as its potential use as a universal sampler.
S. Seethapathy, T. Gorecki, University of Waterloo, Waterloo, ON, Canada.
Passive air samplers are either based on the principle of diffusion (diffusive samplers) or permeation through a membrane (permeation samplers). Passive air sampling has many advantages, including simplicity, low cost, and ease of use, but the measurement results might be affected by temperature and humidity variations. Another potential disadvantage is the need for the passive samplers to be calibrated for each individual analyte prior to field deployment, particularly for permeation samplers. Active sampling techniques do not share most of these limitations; therefore, they are often preferred despite their higher costs and complexity.
A simple, new permeation passive sampler equipped with a polydimethylsiloxane (PDMS) membrane has been designed in an attempt to overcome the major limitations of passive sampling techniques. Permeability of a polymeric membrane toward an analyte is the product of the analyte diffusion coefficient and its solubility in the membrane material. While the solubility of organic compounds in PDMS decreases with temperature, their diffusion coefficients increase with temperature. Consequently, analyte permeability through the membrane — hence, also its uptake rate — is expected to be practically independent of temperature. The effect of moisture in the atmosphere on the uptake rate of the sampler and on sorbent capacity is significantly reduced owing to the hydrophobicity of PDMS. In addition, linear temperature-programmed retention indices (LTPRIs) of the analytes determined in gas chromatographic columns coated with pure PDMS stationary phases can be used to estimate the calibration constants of the individual analytes without the need for calibration with standard gas mixtures. The theoretical principles behind this approach along with experimental results will be discussed.
K. Henry, K. Schmerber, Hellman & Associates Inc., Golden, CO; M. Rothney, A. Doane, Roche Colorado Corp., Boulder, CO.
The sampling and analysis of bulk solvents from incoming tankers is a critical and necessary activity to protect the quality of pharmaceutical compounds synthesized at Roche Colorado Corp. (RCC). Repeated industrial hygiene studies of tanker truck solvent sampling activities determined exceedance of immediately dangerous to life and health (IDLH) levels for several select solvents. Historically, the manual practice of depressurizing and sampling tankers via the top dome did not allow for solvent vapor suppression. Loose-fitting supplied-air respirators were used to provide employee protection. However, the respirators were not designed for use in IDLH atmospheres. In addition, the situation was complicated due to the fact not all tanker sampling locations provided the necessary fall protection required for the task. To address these issues, a central solvent tanker sampling station with a truck access platform and dedicated local exhaust ventilation was designed and implemented. The inspection platform provided safe, easy access to the tanker dome and included a high-volume fan with an articulating local exhaust hood for solvent vapor capture. Field validation after installation indicated that the tanker sampling station was successful at not only containing airborne solvent concentrations below IDLH values but also was well below applicable occupational exposure limits. The engineering controls effectively eliminated the reliance on respiratory protection during tanker sampling. These results verified that the intended goal of protecting tanker sampling personnel was achieved with continued alignment of RCC’s commitment to provide a workplace free of recognized health and safety hazards.
D. Herbert, V. Sundaram, L. Albin, Y. Lu, S. Bagchi, Z. Li, Purdue University, West Lafayette, IN.
Real-time carbon dioxide monitoring in occupant breathing zones allows for microclimate control of indoor air quality. We demonstrate a system of low-cost carbon dioxide and temperature sensors that can wirelessly transmit air quality data to a central computer where control decisions can be made. From an engineering approach, collected data allows the climate control system both to accurately regulate the air quality and to quickly respond to changes in room occupation and air quality. When the room is occupied, carbon dioxide and temperature levels rise, and the climate control system increases airflow. When the room is unoccupied, the amount of airflow can be reduced correspondingly. This technology has not previously been available due to the cost of sensors and wiring requirements, thus limiting sensor locations to return ductworks in single-zone auditorium and classroom spaces. Our approach saves energy by not requiring a climate control system to anticipate maximum needs; rather, it adjusts system output to meet current needs. Low-cost sensors allow us to use this concept at the individual room level and tie multiple individual rooms together to optimize heating, ventilating, and air conditioning energy consumption while meeting air quality requirements. The new system can be deployed with minimal disruption to the existing system. Our sensors combine several technologies along with custom software and packaging to provide this level of service at low cost. We deploy prototype sensors in a typical conference room environment at our university. In addition to calculating the energy savings, we will show that our new technology allows air quality measurements in smaller multizone or individually controlled areas.