Poly(dimethylsiloxane) as passive sampler material for hydrophobic chemicals: effect of chemical properties and sampler characteristics on partitioning and equilibration times

Information about sampling rates and equilibration times of passive samplers is essential in their calibration in field monitoring studies as well as sorption studies. The kinetics of a sampler depends on the distribution coefficient between the sampler material and aqueous phase and the exchange rates of chemicals between these phases. In this study, the elimination kinetics of four poly(dimethylsiloxane) (PDMS) passive samplers with different surface-volume ratios are compared. The samplers were loaded with polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) that cover a broad range of hydrophobicities. The surface-volume ratios of the samplers could largely explain the observed kinetics. Furthermore, a simple diffusion-based model illustrates that the exchange of chemicals was limited by diffusion through the aqueous diffusion layer surrounding the sampler. On the basis of this simple diffusion model, equilibration times are predicted for organic chemicals that vary in hydrophobicity and samplers with different dimensions and polymeric phases. This information is of importance in the selection of a passive sampler for a specific purpose.     

气旋式生物气溶胶采样器采集物理效率评价方法研究

为了评价气旋式生物气溶胶采样器的采集效率,搭建了颗粒物浓度均匀、稳定的静态箱法评价装置,对国内2款气旋式生物气溶胶采样器的采集物理效率进行了测量,最终拟合得到采集效率曲线。测量结果表明：在品牌一采样器的固定采样流量下,其采集物理效率曲线的D_a50(采集效率为50%时的空气动力学直径)为0.91μm;品牌二采样器具有5种可调的采样流量,在不同流量下D_a50分别为1.60μm、1.36μm、1.19μm、1.06μm和1.05μm。对比了使用初始容量分别为15 mL和7.5 mL的采样液得到的品牌二采样器的采集物理效率,发现采样液初始容量较少时,采集物理效率偏低。为气旋式生物气溶胶采样器性能的评价方法提供了参考。     

Development of an infrared hollow waveguide as a sensing device for detection of organic compounds in aqueous solutions

In this paper, a new detection method based on an infrared hollow waveguide is developed to detect semivolatile to nonvolatile organic compounds in aqueous solutions. The hollow waveguide is produced by chemical deposition of silver on the inner surface of a polyethylene tube. The surface of the silver layer is further coated with a hydrophobic film to attract organic compounds in aqueous solution. Samples were pumped through this hollow waveguide sampler and organic compounds were attracted onto the hydrophobic film. After removal of the residual water molecules in the hollow waveguide sampler, organic compounds can be sensed by conventional Fourier transform infrared (FT-IR) spectrometry. Theoretical aspects of this type of sampler are also presented. The derived analytical equations for this type of sampler were consistent with experimental data. Under the condition of constant hydrophobic film volume, high linearity (R(2) equal to 0.9993) between the concentration of analyte and the detected signal was obtained for concentrations in the range from 2.5 ppm to 50 ppb. By co-adding 100 scans with 4 cm(-)(1) resolution, the typical detection limit in this type of sensing method can be lower than 10 ppb. Several factors such as sampling flow rate, sampling time, and hydrophobic film volume were also investigated in this work.     

基于空气动力学的浮游菌采样器采集物理效率检测方法的研究

基于空气动力学原理,提出了一种针对浮游菌采样器采集物理效率的新型检测方法,并搭建了检测装置,可以得到连续的采样效率曲线,直观获取不同动力学粒径对应的采集物理效率。分别评价了2款国产及1款进口的浮游菌采样器采集物理效率,结果发现国产采样器采样效率不及进口品牌,质量还有待提升。研究了多分散的亚利桑那超细试验粉尘与单分散颗粒物标物检测结果的差异,发现国产采样器的差异大于进口采样器。所提检测方法有助于提高浮游菌采样器采集物理效率检测的准确性、科学性及检测效率。     

Measuring aerosols generated inside armoured vehicles perforated by depleted uranium ammunition

In response to questions raised after the Gulf War about the health significance of exposure to depleted uranium (DU), the US Department of Defense initiated a study designed to provide an improved scientific basis for assessment of possible health effects on soldiers in vehicles struck by these munitions. As part of this study, a series of DU penetrators were fired at an Abrams tank and a Bradley fighting vehicle, and the aerosols generated by vehicle perforation were collected and characterised. A robust sampling system was designed to collect aerosols in this difficult environment and monitor continuously the sampler flow rates. The aerosol samplers selected for these tests included filter cassettes, cascade impactors, a five-stage cyclone and a moving filter. Sampler redundancy was an integral part of the sampling system to offset losses from fragment damage. Wipe surveys and deposition trays collected removable deposited particulate matter. Interior aerosols were analysed for uranium concentration and particle size distribution as a function of time. They were also analysed for uranium oxide phases, particle morphology and dissolution in vitro. These data, currently under independent peer review, will provide input for future prospective and retrospective dose and health risk assessments of inhaled or ingested DU aerosols. This paper briefly discusses the target vehicles, firing trajectories, aerosol samplers and instrumentation control systems, and the types of analyses conducted on the samples.     

Passive sampler for dissolved organic matter in freshwater environments

A passive sampler for the isolation of dissolved organic matter (DOM) from freshwater environments is described. The sampler consists of a molecular weight selective membrane (1000 kDa) and an anion exchange resin (diethylaminoethylcellulose (DEAE-cellulose)). NMR indicates the samplers isolate DOM that is nearly indistinguishable from that isolated using the batch DEAE-cellulose procedure. In a comparative study DOM isolated from Lake Ontario cost approximately 0.30 dollars/mg to isolate using the passive samplers while DOM isolated using the traditional batch procedure cost approximately 8-10 dollars/mg. The samplers have been shown to be effective in a range of freshwater environments including a large inland lake (Lake Ontario), fast flowing tributary, and wetland. Large amounts (gram quantities of DOM) can be easily isolated by increasing the size or number of samplers deployed. Samplers are easy to construct, negate the need for pressure filtering, and also permit a range of temporal and spatial experiments that would be very difficult or impossible to perform using conventional approaches. For example, DOM can be monitored on a regular basis at numerous different locations, or samplers could be set at different depths in large lakes. Furthermore, they could potentially be deployed into hard to reach environments such as wells, groundwater aquifers, etc., and as they are easy to use, they can be mailed to colleagues or included with expeditions going to difficult to reach places such as the Arctic and Antarctic.     

Sorbent-impregnated polyurethane foam disk for passive air sampling of volatile fluorinated chemicals

A passive air sampler comprising a polyurethane foam (PUF) disk impregnated with XAD-4 powder has been developed. This sorbent-impregnated PUF (SIP) disk builds on previous work using PUF disk passive air samplers that have been effective in spatial air mapping studies of nonpolar hydrophobic chemicals, without the need of electricity or expensive air sampling equipment. In this study, PUF disks and SIP disks are calibrated for sampling volatile polyfluorinated chemicals--specifically, the fluorotelomer alcohols (FTOHs) and perfluoroalkyl sulfonamides (PFASs). Results demonstrate the low sorptive capacity of the PUF disk samplers, particularly for the FTOHs, with PUF disks reaching equilibrium within 1 day, after collecting approximately 0.4 and 1.2 m3 of air for 8:2 FTOH and 10:2 FTOH, respectively. This limits their use for these target compounds when time-weighted, linear-phase sampling is desired. The presence of just 0.4 g of XAD powder in the SIP disks greatly increases the sorptive capacity (by approximately 2 orders of magnitude for the FTOHs) and provides linear-phase sampling for a period of several weeks. PUF-air partition coefficients, KPUF-A, calculated for the FTOHs and PFASs are considerably lower than values predicted using previously established correlations against the octanol-air partition coefficient, KOA, demonstrating the unique partitioning behavior of the polyfluorinated chemicals. Using results from these calibration tests, air concentrations of FTOHs were derived from PUF disk samples that were deployed in 52 homes in Ottawa, Canada, during 2002/2003. These represent the first comprehensive measurements of FTOHs in indoor air in North America. Range and (geometric mean) air concentrations (pg m-3) were 261-28 900 (2070) for 8:2 FTOH and 104-9210 (890) for 10:2 FTOH. These air concentrations are orders of magnitude higher than observed for outdoor air, establishing indoor environments as important for human exposure and also as potential sources to the larger environment.     

Comparison of annular diffusion denuder and high volume air samplers for measuring per- and polyfluoroalkyl substances in the atmosphere

Overestimation of the particle phase concentration collected on glass-fiber filters (GFFs) has been reported for perfluoroalkyl carboxylic acids (PFCAs) using conventional high volume air samplers. In this study, per- and polyfluoroalkyl substances (PFASs) were determined in the gas and particulate phases using colocated annular diffusion denuder and high volume air samplers at a semiurban site in Toronto, Canada, in winter 2010. Samples were analyzed for 7 PFAS classes (i.e., PFCAs, perfluoro-alkane sulfonic acids (PFSAs), fluorotelomer alcohols (FTOHs), fluorotelomer methacrylates (FTMACs), fluorotelomer acrylates (FTACs), perfluorooctane sulfonamides (FOSAs), and perfluorooctane sulfonamidoethanols (FOSEs)). The gas diffusion coefficients for individual PFASs were calculated and the denuder performance was evaluated. Modeled subcooled liquid vapor pressures (p(L)) correlated well with the vapor phase breakthrough for the denuder and high volume air systems. Total air concentrations for PFASs measured using annular diffusion denuders and high volume samplers were in agreement within a factor of 4; however, much greater differences were observed for measurements of gas-particle partitioning. Vapor phase PFSAs and PFCAs can adsorb to the GFF using high volume air samplers, resulting in much higher particle-associated fractions for these chemicals compared to the annular diffusion denuder sampler. This effect was not observed for the FTOHs, FTMACs, FTACs, FOSAs, and FOSEs. Thus, for investigations of gas-particle partitioning of PFSAs and PFCAs, the diffusion denuder sampler is the preferred method. The results of this study improve our understanding of the gas-particle partitioning of PFASs, which is important for modeling their long-range transport in air.     

In vivo biocompatibility and analytical performance of intravascular amperometric oxygen sensors prepared with improved nitric oxide-releasing silicone rubber coating

The in vivo biocompatibility and analytical performance of amperometric oxygen-sensing catheters prepared with a new type of nitric oxide (NO)-releasing silicone rubber polymer (DACA/N2O2 SR) is reported. The NO-release silicone rubber coating contains diazeniumdiolated secondary amine sites covalently anchored to a dimethylsiloxane matrix. Narrow diameter (0.9 mm, o.d.) silicone rubber tubing coated with this polymer can be employed to construct functional oxygen-sensing catheters that release NO continuously at levels > 1 x 10(-10) mol/cm2-min for more than 20 h. In vivo evaluation of such sensors within the carotid and femoral arteries of swine over a 16-h time period demonstrates that sensors prepared with the new NO-release coating exhibit no significant platelet adhesion or thrombus formation, but control sensors (non-NO release) implanted within the same animals do show a high propensity for cell adhesion and bulk clot formation. Furthermore, the in vivo analytical data provided by sensors fabricated with NO-release coatings (N = 9) are shown to be statistically equivalent to PO2 levels measured in vitro on discrete samples of blood. Control sensors (N = 9) placed within the same animals yield average PO2 values that are statistically different (p < or = 0.05) (lower) from both the levels measured on discrete samples and those provided by the NO-release sensors over a 16-h in vivo monitoring period.     

Phase-plane-derived distortion modeling of a fast and accurate digitizing sampler

Continued efforts to model the distortion behavior of custom-designed digitizing samplers for accurate measurement of dynamic signals are reported. This work is part of ongoing efforts at the National Institute of Standards and Technology (NIST) to advance the state of the art in waveform sampling metrology. In this paper, an analytic error model for a sampler having a -3-dB 6-GHz bandwidth is described. The model is derived from examination of the sampler's error behavior in the phase plane. The model takes as inputs the per-sample estimates of signal amplitude, first derivative, and second derivative, where the derivatives are with respect to time. The model's analytic form consists of polynomials in these terms, which are chosen from consideration of the voltage dependence of the digitizer input capacitance and the previously studied error behavior in a predecessor digitizer. At 1 GHz, an improvement in total harmonic distortion from -32 to -46 dB is obtained when model-generated sample corrections are applied to the waveform. The effect of timebase distortion in the sampling system is also accounted for and corrected. The inclusion of second-derivative dependence in the model is shown to improve the model's fit to the measured data by providing fine temporal adjustment of the fitted waveform.     

Four passive sampling elements (quatrefoil)--I. Monitoring radon and its progeny by surface-contamination monitors

Four passive sampling elements (quatrefoil) have been recently developed, which transform airborne radionuclides into surface-bound radionuclides. These samplers, once exposed, result in thin radiation sources that can be detected by any real-time or passive detector. In particular, by using a large collecting-area sampler with a low surface density (g cm(-2)), it is possible to measure radon and its decay products by beta surface-contamination monitors, which are rarely used for these applications. The results obtained to date prove that it is finally possible to carry out the measurements of radon (and its decay products) indoors, in soil and in water simply by a Pancake Geiger-Muller counter. Emphasis will be given to those measurements, which are difficult, if not impossible, to carry out with existing technologies.     

Time-weighted average sampling with solid-phase microextraction device: implications for enhanced personal exposure monitoring to airborne pollutants

The solid-phase microextraction (SPME) device is used as a time-weighted average (TWA) sampler for gas-phase analytes by retracting the coated fiber a known distance into its needle housing during the sampling period. Unlike in conventional spot sampling with SPME, the TWA sampling approach does not allow the analytes to reach equilibrium with the fiber coating, but rather they diffuse through the opening in the needle to the location of the sorbent. The amount of analytes accumulated over time gives the measurement of the average concentration to which the device was exposed to. Depending on the sorbent used as the sink, TWA sampling for various analytes is possible with times ranging from 15 min to at least 16 h. Both the poly(dimethylsiloxane) (PDMS) and poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber coating phases were tested, with the latter employing on-fiber derivatization for reactive carbonyl compounds, e.g., formaldehyde. Described herein are the theoretical and practical considerations for using the SPME device as a TWA sampler.     

Solid-phase microextraction field sampler

To facilitate the use of solid-phase microextraction (SPME) for field sampling, a new field sampler was designed and tested. The sampler was versatile and user-friendly. The SPME fiber can be positioned precisely inside the needle for time-weighted average sampling or exposed completely outside the needle for grab sampling. The needle is protected within a shield at all times, hereby eliminating the risk of operator injury and fiber damage. A replaceable Teflon cap is used to seal the needle to preserve sample integrity. Factors that affect the preservation of sample integrity (sorbent efficiency, temperature, sealing materials) were studied. The use of a highly efficient sorbent for the fiber is recommended as the first choice for the preservation of sample integrity. Teflon was a good material for sealing the fiber needle, had little memory effect, and could be used repeatedly. To address adsorption of high boiling point compounds on fiber needles, several kinds of deactivated needles were evaluated. RSC-2 fiber needles were the more effective. A preliminary field sampling investigation demonstrated the validity of the new SPME device for field applications.     

Measurement of 2,4-toluene diisocyanate concentrations by different samplers

The standard sampling methods for toluene diisocyanate (TDI) only collect total TDI without separating the aerosol and gas phases. There are few other samplers, such as the dual filter, triple filter and annular denuder systems (ADS), which are able to sample the aerosol and gas phases simultaneously. This field study was conducted at two workplaces to access the total 2,4-TDI and the gaseous and aerosol TDI concentrations by different samplers simultaneously. In addition to the standard sampling time of 15 min, sampling was done for 30 and 60 min to study the effect of sampling time on the measured 2,4-TDI concentrations. Test results at two workplaces show that gas-phase 2,4-TDI is the predominant species and the aerosol phase concentration is very small. The measurements using various samplers show that the sampling time influences the sampled TDI concentration considerably which may be due to reaction of TDI with water vapor and polyo in the sampling process. It is evident that as sampling time increases the TDI concentration decreases. Laboratory test was also conducted using pure gas-phase 2,4-TDI to confirm the sampling time effect on the measured concentrations found in the field study.     

Membrane-enclosed sorptive coating. an integrative passive sampler for monitoring organic contaminants in water.

An integrative sampler that consists of a bar coated with poly(dimethylsiloxane) (PDMS) enclosed in a dialysis membrane bag has been developed combining the advantages of the passive sampling approach with solventless preconcentration of organic solutes from aqueous matrixes and subsequent desorption of the sequestered analytes on-line with a capillary GC/MS system. The performance of the sampler was tested for integrative sampling of hydrophobic persistent organic pollutants including gamma-hexachlorocyclohexane, hexachlorobenzene, 2,2'-bis(4-chlorophenyl)-1,1'-dichloroethylene, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls in the laboratory in a continuous-flow system. Linear uptake of all test analytes during exposure periods up to one week has been observed, and concentration proportionality of response of the sampler has been demonstrated. Over the range of controlled laboratory conditions, the magnitude of sampling rate values varied from 47 to 700 microL h(-1) per sampler. The uptake rate of chemicals was dependent on their molecular mass, as well as on the partition coefficient between the PDMS and water. A decrease in sampling rates with decreasing water temperature was observed. The sampling device has the potential to detect low aqueous concentrations (ng to pg L(-1)) of test substances.     

A miniature biochip system for detection of aerosolized Bacillus globigii spores

The feasibility of using a novel detection scheme for the analysis of biological warfare agents is demonstrated using Bacillus globigii spores, a surrogate species for Bacillus anthracis. In this paper, a sensitive and selective enzyme-linked immunosorbent assay using a novel fluorogenic alkaline phosphatase substrate (dimethylacridinone phosphate) is combined with a compact biochip detection system, which includes a miniature diode laser for excitation. Detection of aerosolized spores was achieved by coupling the miniature system to a portable bioaerosol sampler, and the performance of the antibody-based recognition and enzyme amplification method was evaluated. The bioassay performance was found to be compatible with the air sampling device, and the enzymatic amplification was found to be an attractive amplification method for detection of low spore concentrations. The combined portable bioaerosol sampler and miniature biochip system detected 100 B. globigii spores, corresponding to 17 aerosolized spores/L of air. Moreover, the incorporation of the miniature diode laser with the self-contained biochip design allows for a compact system that is readily adaptable to field use. In addition, these studies have included investigations into the tradeoff between assay time and sensitivity.     

Calibration of permeation passive samplers with silicone membranes based on physicochemical properties of the analytes

Passive sampling is a very attractive alternative to active sampling due to its simplicity and low cost. Among the passive samplers used in air analysis, permeation passive samplers are the least affected by ambient conditions, including humidity, air currents, and temperature changes. The biggest drawback of permeation passive samplers is the need to calibrate them experimentally for each individual target analyte. The paper presents the results of research on the calibration of permeation passive samplers based on physicochemical properties of the analytes. Strong correlations were found between the calibration constants of the samplers and the number of carbon atoms among families of compounds (R2 ranging from 0.8507 for alcohols to 0.9995 for aromatic hydrocarbons), the molecular weights of the compounds (R2 = 0.8742), their boiling points (R2 = 0.8911), and linear temperature-programmed retention indexes (R2 = 0.9225). The last correlation makes it possible to estimate the calibration constants for unidentified analytes, which is impossible when the conventional procedure is used. This makes it possible to deploy permeation passive samplers in the same way in which active sampling is deployed.     

Time-weighted average passive sampling with a solid-phase microextraction device

A modified Solid-Phase Microextraction (SPME) device has been used as a passive sampler to determine the time-weighted average (TWA) concentration of volatile organic compounds (VOCs) in air. Unlike conventional sampling with SPME, in which the fiber is extended outside its needle housing, during TWA passive sampling, the fiber is retracted a known distance into its needle housing. The SPME passive sampler collects the VOCs by the mechanism of molecular diffusion and sorption on to a coated fiber as collection medium. This process has been shown to be described by Fick's first law of diffusion, whereby determination of the amounts of analytes accumulated over time enable measurement of the TWA concentration to which the sampler was exposed. A series of fibers, 100-microm poly(dimethylsiloxane), 65-microm poly(dimethylsiloxane)/divinylbenzene, and 75-microm Carboxen/poly(dimethylsiloxane), were tested for their "zero sink", face velocity, and response time behavior. Of the fibers tested, that coated with 75-microm Carboxen/poly(dimethylsiloxane) was found to be an excellent passive sampler for VOCs. TWA passive sampling with a SPME device was shown to be almost independent of face velocity and to be more tolerant of high and low analyte concentrations and long and short sampling times, because of the ease with which the diffusion path length could be changed. It was found that environmental conditions, e.g., temperature, pressure, relative humidity, and ozone, have little or no effect on sampling. The 75-microm Carboxen/poly(dimethylsiloxane) fiber can retain VOCs for up to two weeks without significant loss. When the SPME device was tested in the field and the results were compared with those from National Institute of Occupational Health and Safety method 1501, good agreement was obtained.     

Broadband sampling oscilloscope characterization with the“Nose-to-Nose” calibration procedure: a theoretical andpractical analysis

In the past the “nose-to-nose” calibration procedure has been introduced as probably the most accurate method to determine the impulse response of broadband sampling oscilloscopes like the HP54124T. The method is based on the hypothesis “sampler kick-out equals oscilloscope impulse response”. This hypothesis was originally based on an intuitive approach and was later verified experimentally (comparison with power measurements) as well as with SPICE simulations. Until now, however, there was no generalized mathematical evidence supporting this basic hypothesis. In this paper a mathematical theory is developed, which starts from a generalized sampler equivalent scheme, and which shows that, under conditions which are valid in practice, the sampler kick-out indeed equals the sampler impulse response. Experimental results are reported concerning the accuracy and precision of the calibration procedure. These experiments involve the investigation of experiment repeatability, noise, sampler linearity and timebase effects     

Development of an automatic smear sampler and evaluation of surface contamination

The surface contamination level of a radiation-controlled area is measured periodically according to atomic energy law and connection regulations. The measurement of surface contamination by an indirect method is subject to various kinds of error depending on the sampling person and consumes much time and effort in the sampling of large nuclear facilities. In this research, an automatic smear sampler is developed to solve these problems. The developed equipment is composed of a rotating sampling part, a sample transferring part, a power supply part a control part, and vacuum part. It improved the efficiency of estimation of the surface contamination level achieved periodically in a radiation-controlled area. Using an automatic smear sampler developed in this research, it is confirmed that radioactive contaminated materials are uniformly transferred to smear paper more than any sampling method by an operator.