Assessment of Uncertainty in Measurements of Reduced Sulfur Compounds by Active Sampling on Tenax TA® Tubes (original) (raw)
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Microchemical Journal, 2017
In the past two decades there has been increasing interest in monitoring volatile reduced sulfur compounds (RSCs) in the atmosphere relatively to their unpleasant smell and their low olfactory threshold. The olfactory annoyance is considered as an important environmental issue, especially since the industrial development near residential areas. The volatile reduced sulfur compounds including mercaptans (RSH) and sulfides (RSR') are emitted from different sources as sewage, waste treatment plant and chemical industry. A preconcentration step before analysis is required in case of odor nuisance at low concentration (a few ppb). While active sampling through cartridges filled with Tenax TA® is recognized as the most suitable method for the measurements of RSCs in ambient air, any comprehensive qualification and validation of this sampling method was carried out. In this work, breakthrough volumes were determined for 6 different RSCs (methylmercaptan, ethylmercaptan, dimethylsulfide, isopropylmercaptan, tertbutylmercaptan, diethylsulfide) at ppb levels on active sampling tubes packed with 250 mg of Tenax TA®. Breakthrough volumes range from 1 to N 5 L, for an optimal flow of 25 mL min −1. Except for methylmercaptan, for which it was estimated to b0.2 L at 20 ppb and around 2 L at 1 ppb. No quantitative measurement could be assured for methylmercaptan due to low breakthrough volume; whereas for the 5 others RSCs, the global measurement uncertainties linked to the active sampling (matrix interferences, storage), and to the analytical performances of TD-GC-FID/FPD analysis were calculated. Analytical uncertainties don't exceed 25%: the accuracy of the standard preparation and the lack of fit of calibration are the two major contributors. However, taking into account the sampling uncertainties, global relative concentration uncertainties reach maximal values of 74 and 59% for mercaptans and sulfides respectively considering a storage at −21°C and a relative humidity of 85% (at 20°C). Storage contribution was estimated to 2% for sulfides and 34% for mercaptans and relative humidity contribution between 55% and 85% for the sulfides and mercaptans at a relative humidity of 85% (at 20°C).
Microchemical Journal, 2018
Odour annoyance forms the main source of environmental stress in residents living nearby industrial or agricultural fields. However, despite a relative simplicity of odour measurement at the emission source, odour measurement in the field is a quite more complicated task. Because of their low odour threshold and offensive odour, this study focuses on 6 reduced sulfur compounds (RSCs): methylmercaptan (MM), ethylmercaptan (EM), dimethylsulfide (DMS), isopropylmercaptan (IPM), tertbutylmercatpan (TBM), diethylsulfide (DES). Because of their very low concentrations in ambient air (few ppb), a preconcentration step is usually required. The literature points Tenax TA® as the more suitable sorbent for sulfur compounds adsorption but shows also an important impact of humidity and storage parameters inducing an underestimation of sulfur ambient air concentrations. So only qualitative or semi-quantitative data results are obtained with Tenax TA® samplings of targeted compounds. To guarantee quantitative concentration data, a new sampling device, using a S-Sorbent Tube 450 combined with an optimal drying device, was performed and optimized sampling and analysis parameters were determined. The assessment of uncertainties attests of quantitative measurements for 5 of the 6 RSCs (EM, DMS, IPM, TBM, DES) with relative expanded uncertainties less than 33 % considering that samples were stored properly in freeze during 7 days. Only semi
Sampling and analysis of sulphur containing volatile organic compounds at low concentrations
Sampling and analysis of sulphur-containing volatile organic compounds (S-VOCs) is not straightforward, since S-VOCs can be observed by human nose in very low concentrations. In addition, most of the people find these odours very unpleasant. This paper presents the results of emission measurements originating from a rendering plant and development of measurement strategy to ensure the reliability of the results. These results are needed e.g. in designing of an optimal abatement system. Three different adsorbents are tested in laboratory and industrial scales including Tenax TA, Carbograph 1 TD and Carboxen 1000 in sampling of methyl mercaptane (MM), dimethylsulphide (DMS) in dry and moist conditions. It was found that none of the adsorbents tested, was really good in sampling of methyl mercaptane and dimethyl disulphide. Tenax TA, even having a low breakthrough for tested compounds, can be used in moist conditions. A multiple-bed adsorbent showed the best performance in dry conditions.
2012
A monitoring program based on an indirect method was conducted to assess the approximation of the olfactory impact in several wastewater treatment plants (in the present work, only one is shown). The method uses H2S passive sampling using Palmes-type diffusion tubes impregnated with silver nitrate and fluorometric analysis employing fluorescein mercuric acetate. The analytical procedure was validated in the exposure chamber. Exposure periods of at least 4 days are recommended. The quantification limit of the procedure is 0.61 ppb for a 5-day sampling, which allows the H2S immission (ground concentration) level to be measured within its low odor threshold, from 0.5 to 300 ppb. Experimental results suggest an exposure time greater than 4 days, while recovery efficiency of the procedure, 93.0 ± 1.8%, seems not to depend on the amount of H2S collected by the samplers within their application range. The repeatability, expressed as relative standard deviation, is lower than 7%, which is within the limits normally accepted for this type of sampler. Statistical comparison showed that this procedure and the reference method provide analogous accuracy. The proposed procedure was applied in two experimental campaigns, one intensive and the other extensive, and concentrations within the H2S low odor threshold were quantified at each sampling point. From these results, it can be concluded that the procedure shows good potential for monitoring the olfactory impact around facilities where H2S emissions are dominant.Passive samplers are very attractive tools to experimentally tackle a number of air pollution problems, especially those related to odor impact. Their small size and cost permit a denser sampling design and thus a more detailed spatial characterization than other techniques. On the other hand, the large inherent variability in passive sampler measures requires an uncertainty analysis of the chemical species and analytical procedures used.
The effects of sampling materials selection in the collection of reduced sulfur compounds in air
Talanta, 2006
In this study, the analytical bias in the measurements of reduced sulfur compounds (RSC) was investigated in terms of sorptive loss caused by the materials selected for the sample introduction. For the purpose of this study, three vacuum samplers made in the combination of different vacuuming efficiencies (e.g., rapid versus slow sampling) and different materials (i.e., Teflon versus stainless steel (SS)) were tested to evaluate the sampling recovery rate (RR) for five RSCs: H 2 S, CH 3 SH, DMS, CS 2 and DMDS. To make a parallel comparison of RR, the RSC standard samples contained in one bag were transferred to another bag using each sampling system. Their relative contents between, before, and after the transfer were then evaluated between different samplers to assess the sampling bias caused by the interaction between RSC and the sampling material. In the case of the most reactive compound, H 2 S, the sampling loss from the SS inlet line amounted to as high as 45%, while that for the Teflon counterpart was almost insignificant. When the sampling time was arbitrarily elongated (i.e., use of a slow sampler), the sampling loss rate of the SS inlet sampler became more significant with the RR values dropping down from 55 to 70%, across different RSCs. The overall results of our comparative study indicate that the sampling system for the reactive gaseous compounds should be checked for the material feasibility to guarantee sufficient analytical reliability.
Journal of Chromatography A, 2006
This paper addresses the variations that presently exist regarding the definition, determination, and reporting of detection limits for volatile sulphur compounds by gas chromatography with pulsed flame photometric detection (GC-PFPD). Gas standards containing hydrogen sulphide (H 2 S), carbonyl sulphide (COS), sulphur dioxide (SO 2), methyl mercaptan (CH 3 SH), dimethyl sulphide (DMS), carbon disulphide (CS 2), and dimethyl disulphide (DMDS) in concentrations varying from 0.36 ppb (v/v) up to 1.5 ppm (v/v) in nitrogen were prepared with permeation tubes and introduced in the gas chromatograph using a 0.25-ml gas sampling loop. After measuring the PFPD response versus concentration, the method detection limit (MDL), the Hubaux-Vos detection limit (x D), the absolute instrument sensitivity (AIS), and the sulphur detectivity (D s) were determined for each sulphur compound. The results show that the MDL determined by the US Environmental Protection Agency procedure consistently underestimates the minimum concentrations of volatile sulphur compounds that can be practically distinguished from the background noise with the PFPD. The Hubaux-Vos detection limits and the AIS values are several times higher than the MDL, and provide more conservative estimates of the lowest concentrations that can be reliably detected. Sulphur detectivities are well correlated with AIS values but only poorly correlated with MDL values. The AIS is recommended as a reliable and cost-effective measure of detection limit for volatile sulphur compounds by GC-PFPD, since the AIS is easier and faster to determine than the MDL and the Hubaux-Vos detection limit. In addition, this study confirmed that the PFPD response is nearly quadratic with respect to concentration for all volatile sulphur compounds.
Talanta, 2008
The concentrations of seven volatile organic sulfur compounds (VOSCs) in air samples were determined by active collection on multisorbent tubes followed by two-stage thermal desorption and gas chromatography-mass spectrometry. The compounds studied were ethyl mercaptan (CH 3 CH 2 SH), dimethyl sulfide ((CH 3) 2 S), carbon disulfide (CS 2), propyl mercaptan (C 3 H 8 S), butyl mercaptan (C 4 H 10 S), dimethyl disulfide ((CH 3) 2 S 2) and 1-pentanethiol (C 5 H 12 S). Active collection on SilcoSteel multisorbent tubes enabled an air volume of 3000 ml to be sampled without observing breakthrough. This study focused on an exhaustive sampling of several process steps or sections from sewage management plants. A wide range of concentrations was observed. Dimethyl sulfide, carbon disulfide and dimethyl disulfide were the most abundant compounds in all samples, the highest concentrations being 608.5 g m −3 , 658.5 g m −3 and 857.8 g m −3 , respectively. The less appearing compound was ethyl mercaptan, which was only detected in the sludge digestion process at a maximum concentration of 14.8 g m −3. The remaining compounds were detected and measured in about half the samples. The sections with the maximum values of VOSCs involved sludge processes such as mixing, thickening and digestion. The results were also strongly influenced by the design characteristics of the sampling point, e.g. whether the sample was taken at a confined site or in the open air.
Journal of Separation Science, 2013
This study describes the development of an analytical method based on active collection in a multisorbent Tenax TA/Carbograph 1TD tube, followed by thermal desorption and gas chromatography-mass spectrometry for the determination of 16 volatile organic compounds in air samples. The analysed compounds include ozone precursors and odour-causing compounds belonging to different chemical families (sulphur-and nitrogen-containing compounds, aldehydes and terpenes). Two types of sorbents were tested and desorption conditions (temperature, time, and sampling and desorption flow) were evaluated. External calibration was carried out using the multisorbent bed. Method detection limits in the range 0.2-2.0 g•m-3 for 1 L samples were obtained. The method was applied for determining the target compounds in air samples from two different wastewater treatment plants. Most of the compounds were detected and toluene, limonene and nonanal were found in particularly high concentrations with maximum values of 438 g•m-3 , 233 g•m-3 and 382 g•m-3 , respectively.
AIP Conference Proceedings, 2009
Odor samples collected in field research are complex mixtures of hundreds if not thousands of compounds. Research is needed to know how best to sample and analyze these compounds. The main objective of this research was to compare recoveries of a standard gas mixture of 11 odorous compounds from the Carboxen∕PDMS 75 μm SPME fibers, PVF (Tedlar), FEP (Teflon), foil, and PET (Melinex) air sampling bags, sorbent Tenax TA tubes and standard 6 L Stabilizer™ sampling canisters after sample storage for 0.5, 24, and 120 (for sorbent tubes only) hrs at room temperature. The standard gas mixture consisted of 7 volatile fatty acids (VFAs) from acetic to hexanoic, and 4 semi-VOCs including p-cresol, indole, 4-ethylphenol, and 2'-aminoacetophenone with concentrations ranging from 5.1 ppb for indole to 1, 270 ppb for acetic acid. On average, SPME had the highest mean recovery for all 11 gases of 106.2%, and 98.3% for 0.5 and 24 hrs sample storage time, respectively. This was followed by the Tenax TA sorbent tubes (94.8% and 88.3%) for 24 and 120 hrs, respectively; PET bags (71.7% and 47.2%), FEP bags (75.4% and 39.4%), commercial Tedlar bags (67.6% and 22.7%), in-house-made Tedlar bags (47.3% and 37.4%), foil bags (16.4% and 4.3%), and canisters (4.2% and 0.5%), for 0.5 and 24 hrs, respectively. VFAs had higher recoveries than semi-VOCs for all bags and canisters. New FEP bags and new foil bags had the lowest and the highest amounts of chemical impurities, respectively. New commercial Tedlar bags had measurable concentrations of N, N-dimethyl acetamide and phenol. Foil bags had measurable concentrations of acetic, propionic, butyric, valeric and hexanoic acids.