Author: Publisher:
ISBN:
Category : Engineering instruments
Languages : en
Pages : 40
Book Description
Thermal Desorption VOC Sampler
Author: Publisher:
ISBN:
Category : Engineering instruments
Languages : en
Pages : 40
Book Description
Thermal Desorption VOC Sampler: Improvements and Field Trial Performance (Dover AFB).
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
A thermal desorption volatile organic compound sampler developed for the site characterization penetrometer system program was successfully field tested at Dover Air Force Base, Dover, DE. The device was evaluated as an in situ soil sampler in the vadose, capillary, and saturated zones and as a soil vapor sampler in the vadose zone. Comparisons to validation samples are made.
Measurement of Passive Uptake Rates for Volatile Organic Compounds on Commercial Thermal Desorption Tubes and the Effect of Ozone on Sampling
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 34
Book Description
Diffusive or passive sampling methods using commercially filled axial-sampling thermal desorption tubes are widely used for measuring volatile organic compounds (VOCs) in air. The passive sampling method provides a robust, cost effective way to measure air quality with time-averaged concentrations spanning up to a week or more. Sampling rates for VOCs can be calculated using tube geometry and Fick's Law for ideal diffusion behavior or measured experimentally. There is evidence that uptake rates deviate from ideal and may not be constant over time. Therefore, experimentally measured sampling rates are preferred. In this project, a calibration chamber with a continuous stirred tank reactor design and constant VOC source was combined with active sampling to generate a controlled dynamic calibration environment for passive samplers. The chamber air was augmented with a continuous source of 45 VOCs ranging from pentane to diethyl phthalate representing a variety of chemical classes and physiochemical properties. Both passive and active samples were collected on commercially filled Tenax TA thermal desorption tubes over an 11-day period and used to calculate passive sampling rates. A second experiment was designed to determine the impact of ozone on passive sampling by using the calibration chamber to passively load five terpenes on a set of Tenax tubes and then exposing the tubes to different ozone environments with and without ozone scrubbers attached to the tube inlet. During the sampling rate experiment, the measured diffusive uptake was constant for up to seven days for most of the VOCs tested but deviated from linearity for some of the more volatile compounds between seven and eleven days. In the ozone experiment, both exposed and unexposed tubes showed a similar decline in terpene mass over time indicating back diffusion when uncapped tubes were transferred to a clean environment but there was no indication of significant loss by ozone reaction.
Indoor Air
Author: British Standards InstitutionPublisher:
ISBN:
Category :
Languages : en
Pages : 46
Book Description
Indoor, Ambient and Workplace Air
Author: International Organization for StandardizationPublisher:
ISBN:
Category : Air sampling apparatus
Languages : en
Pages : 29
Book Description
Tri-Service Site Characterization and Analysis Penetrometer System (SCAPS) Validation of the Thermal Desorption Sampler for Volatile Organic Compounds
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Volatile organic compounds (VOCs) are among the most frequently identified contaminants in soil and groundwater samples obtained during investigation of hazardous waste sites. The thermal desorption sampler (TDS), was developed for the Site Characterization and Analysis Penetrometer System (SCAPS) program to provide in situ analysis of VOCs in vadose zone and saturated soils. In operation, the TDS captures an estimated quantity of soil below ground, thermally desorbs the VOCs, and transfers them to the surface where they are analyzed on a field poflable ion trap mass spectrometer (ITMS). This analysis is sensitive to the low ppb range for chlorinated solvents and BETX compounds. The TDS was field tested at five geologically distinct sites across the country. Field data were compared to laboratory data (EPA SW-846 Method 8260B (USEPA 1995)) for validation of the technique. Data analysis indicated that the in situ analysis of the primary VOC contaminant at each site demonstrated good correlation with the validation method with a liner regression correlation coefficient between 0.8 and 1.0 and the slope of the regression line between 0.7 and 1.3. Secondary VOC contaminants of lesser concentration demonstrated poorer correlation that could be attributed to the lack of chromatographic separation prior to the ITMS analysis.
Standard Practice for Selection of Sorbents, Sampling, and Thermal Desorption Analysis Procedures for Volatile Organic Compounds in Air
Author: Cost and Performance Report for Tri-Service Site Characterization and Analysis Penetrometer System (SCAPS) Thermal Desorption Sampler for Volatile Organic Compounds
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
The thermal desorption sampler (TDS), developed for the Site Characterization and Analysis Penetrometer System (SCAPS) program provides in situ analysis of volatile organic compounds (VOCs) in vadose zone and saturated soils. In operation, the TDS captures an estimated quantity of soil below ground, thermally desorbs the VOCs, and transfers them to the surface where they are analyzed on a field portable ion trap mass spectrometer (ITMS). This analysis is sensitive to the low ppb range for chlorinated solvents and BETX compounds. The TDS was field tested at five geologically distinct sites across the country. Field data were compared to laboratory data (US EPA SW-846 Method 8260B) for validation of the technique. Data analysis indicated that the in situ analysis of the primary VOC contaminant at each site demonstrated good correlation with the validation method with a liner regression correlation coefficient between 0.8 and 1.0 and the slope of the regression line between 0.7 and 1.3. Secondary VOC contaminants of lesser concentration, demonstrated poorer correlation that could be attributed to the lack of chromatographic separation prior to the ITMS analysis. Cost of operating the TDS system was compared to conventional sample collection and analysis techniques. The main savings produced by using this system were a reduction in time spent characterizing a site, the reduced exposure of workers to contaminants, and the minimization of investigation wastes.
Standard Practice for Selection of Sorbents and Pumped Sampling/Thermal Desorption Analysis Procedures for Volatile Organic Compunds in Air
Author: Demonstration and Validation of the Use of Passive Samplers for Monitoring Soil Vapor Intrusion to Indoor Air
Author: Todd Arthur McAlaryPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
This thesis documents a demonstration/validation of passive diffusive samplers for assessing soil vapor, indoor air and outdoor air concentrations of volatile organic compounds (VOCs) at sites with potential human health risks attributable to subsurface vapor intrusion to indoor air. The study was funded by the United States (U.S.) Department of Defense (DoD) and the U.S. Department of the Navy (DoN). The passive samplers tested included: SKC Ultra and Ultra II, Radiello®, Waterloo Membrane Sampler (WMS), Automated Thermal Desorption (ATD) tubes, and 3M OVM 3500. The program included laboratory testing under controlled conditions for 10 VOCs (including chlorinated ethenes, ethanes, and methanes, as well as aromatic and aliphatic hydrocarbons), spanning a range of properties and including some compounds expected to pose challenges (naphthalene, methyl ethyl ketone). Laboratory tests were performed under conditions of different temperature (17 to 30 oC), relative humidity (30 to 90 % RH), face velocity (0.014 to 0.41 m/s), concentration (1 to 100 parts per billion by volume [ppbv]) and sample duration (1 to 7 days). These conditions were selected to challenge the samplers across a range of conditions likely to be encountered in indoor and outdoor air field sampling programs. A second set of laboratory tests were also conducted at 1, 10 and 100 parts per million by volume (ppmv) to evaluate concentrations of interest for soil vapor monitoring using the same 10 VOCs and constant conditions (80% RH, 30 min exposure, 22 oC). Inter-laboratory testing was performed to assess the variability attributable to the differences between several laboratories used in this study. The program also included field testing of indoor air, outdoor air, sub-slab vapor and deeper soil vapor at several DoD facilities. Indoor and outdoor air samples were collected over durations of 3 to 7 days, and Summa canister samples were collected over the same durations as the passive samples for comparison. Subslab and soil vapor samples were collected with durations ranging from 10 min to 12 days, at depths of about 15 cm (immediately below floor slabs), 1.2 m and 3.7 m. Passive samplers were employed with uptake rates ranging from about 0.05 to almost 100 mL/min and analysis by both thermal desorption and solvent extraction. Mathematical modeling was performed to provide theoretical insight into the potential behavior of passive samplers in the subsurface, and to help select those with uptake rates that would minimize the risk of a negative bias from the starvation effect (which occurs when a passive sampler with a high uptake rate removes VOC vapors from the surroundings faster than they are replenished, resulting in biased concentrations). A flow-through cell apparatus was tested as an option for sampling existing sub-surface probes that are too small to accommodate a passive sampler or sampling a slip-stream of a high-velocity gas (e.g., vent-pipes of mitigation systems). The results of this demonstration show that all of the passive samplers provided data that met the performance criteria for accuracy and precision (relative percent difference less than 45 % for indoor air or 50% for soil vapor compared to conventional active samples and a coefficient of variation less than 30%) under some or most conditions. Exceptions were generally attributable to one or more of five possible causes: poor retention of analytes by the sorbent in the sampler; poor recovery of the analytes from the sorbent; starvation effects, uncertainty in the uptake rate for the specific combination of sampler/compound/conditions, or blank contamination. High (or positive) biases were less common than low biases, and attributed either to blank contamination, or to uncertainty in the uptake rates. Most of the passive samplers provided highly reproducible results throughout the demonstrations. This is encouraging because the accuracy can be established using occasional inter-method verification samples (e.g., conventional samples collected beside the passive samples for the same duration), and the field-calibrated uptake rates will be appropriate for other passive samples collected under similar conditions. Furthermore, this research demonstrated for the first time that passive samplers can be used to quantify soil vapor concentrations with accuracy and precision comparable to conventional methods. Passive samplers are generally easier to use than conventional methods (Summa canisters and active ATD tubes) and minimal training is required for most applications. A modest increase in effort is needed to select the appropriate sampler, sorbent and sample duration for the site-specific chemicals of concern and desired reporting limits compared to Summa canisters and EPA Method TO-15. As the number of samples in a given program increases, the initial cost of sampling design becomes a smaller fraction of the overall total cost, and the passive samplers gain a significant cost advantage because of the simplicity of the sampling protocols and reduced shipping charges.