Quality control in quantification of volatile organic compounds analysed by thermal desorption-gas chromatography-mass spectrometry
ABSTRACT This paper presents a detailed study on the calibration of a thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS)-based methodology for quantification of volatile organic compounds (VOCs) in gaseous and liquid samples. For the first time, it is documented to what extent three widely encountered problems affect precise and accurate quantification, and solutions to improve calibration are proposed. The first issue deals with the limited precision in MS quantification, as exemplified by high relative standard deviations (up to 40%, n=5) on response factors of a set of 69 selected VOCs in a volatility range from 16 Pa to 85 kPa at 298 K. The addition of [(2)H(8)]toluene as an internal standard, in gaseous or liquid phase, improves this imprecision by a factor of 5. Second, the matrix in which the standard is dissolved is shown to be highly important towards calibration. Quantification of gaseous VOCs loaded on a sorbent tube using response factors obtained with liquid standards results in systematic deviations of 40-80%. Relative response factors determined by the analysis of sorbent tubes loaded with both analytes and [(2)H(8)]toluene from liquid phase are shown to offer a reliable alternative for quantification of airborne VOCs, without need for expensive and often hardly available gaseous standards. Third, a strategy is proposed involving the determination of a relative response factor being representative for a group of analytes with similar functionalities and electron impact fragmentation patterns. This group method approach indicates to be useful (RSD approximately 10%) for quantifying analytes belonging to that class but having no standards available.
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ABSTRACT: Estimating odor emissions from landfill sites is a complicated task because of the various chemical and biological species that exist in landfill gases. In this study, the relative concentration of ethanol and other odorous compounds emitted from the working surface at a landfill in China was analyzed. Gas sampling was conducted at the landfill on a number of selected days from March 2012 to March 2014, which represented different periods throughout the two years. A total of 41, 59, 66, 54, 63, 54, 41, and 42 species of odorous compounds were identified and quantified in eight sampling activities, respectively; a number of 86 species of odorous compounds were identified and quantified all together in the study. The measured odorous compounds were classified into six different categories (Oxygenated compounds, Halogenated compounds, Terpenes, Sulfur compounds, Aromatics, and Hydrocarbons). The total average concentrations of the oxygenated compounds, sulfur compounds, aromatics, halogenated compounds, hydrocarbons, and terpenes were 2.450 mg/m3, 0.246 mg/m3, 0.203 mg/m3, 0.319 mg/m3, 0.530 mg/m3, and 0.217 mg/m3, respectively. The relative concentrations of 59 odorous compounds with respect to the concentration of ethyl alcohol (1000 ppm) were determined. The dominant contaminants that cause odor pollution around the landfill are ethyl sulfide, methyl mercaptan, acetaldehyde, and hydrogen sulfide; dimethyl disulfide and dimethyl sulfide also contribute to the pollution to a certain degree.PLoS ONE 03/2015; 10(3):e0119305. DOI:10.1371/journal.pone.0119305 · 3.53 Impact Factor
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ABSTRACT: The bumblebee Bombus terrestris is a general pollinator in Europe and also highly suitable as greenhouse pollinator of various agricultural and horticultural crops such as tomato, sweet pepper or strawberry. Here, we highlight the importance of volatile emissions for the attractiveness and pollination efficiency of strawberry varieties, starting from the unique observation that two related strawberry varieties are pollinated to a different extent when cultivated together. In a flight cage Fragaria × ananassa var. ‘Sonata’ was pollinated more frequently (>2 times) and with longer-duration visits (11.2 vs. 6.7 s) by B. terrestris as compared to var. ‘Elsanta.’ To investigate whether this visitation difference could be attributed to differential production of flower volatile compounds, we quantified and analyzed the floral emissions of both varieties. Samples of var. ‘Elsanta’ contained more green leaf volatiles such as E-2-hexenal (0.53 vs. 0 ng/3 flowers), Z-3-hexenol (2.26 vs. 0.20 ng/3 flowers) and Z-3-hexenyl acetate (2.15 vs. 0.46 ng/3 flowers) which are known to play a role in plant defense. In a third series of experiments, we determined olfactory responses of B. terrestris to some similar individual synthetic green leaf volatiles presented in a Y-tube olfactometer. B. terrestris workers responded in an aversive manner to these volatile compounds compared to purified air. Since the floral bouquet of var. ‘Elsanta’ contains more green leaf volatiles, bumblebees will exhibit a preference for var. ‘Sonata.’ Our observations suggest that the pollination preference for ‘Sonata’ is due to being ‘less repellent’ instead of ‘more attractive’ than ‘Elsanta,’ with variety-specific flower emissions lying at the basis.Arthropod-Plant Interactions 06/2015; 9(3). DOI:10.1007/s11829-015-9375-y · 1.18 Impact Factor
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ABSTRACT: Temporal variation (seasonal and daily) of odor emission on the working face of a large sanitary landfill in China was characterized through a 2 yearlong case study. Odor pollution was most serious in spring and autumn, while lower odor concentrations were detected in summer and winter. The daily fluctuation of odor concentration on the working face showed that 2:00 am, 6:00 am, 2:00 pm and 10:00 pm were the ''most probable times'' for odor pollution occurrence, which deserves focused attention in odor control projects. Correlations analysis found that 41% of the variance in odor concentrations can be explained by the chemical concentrations of odorous compounds. Moreover, the selection criteria for the index of odorous compounds were also established by evaluating the odor concentration, contribution to odor strength and the frequency of each compound present in all the samples. Ethyl alcohol, a-piene, hydrogen sulfide, dimethyl sulfide, limonene, methyl mercaptan, dimethyl disulfide, and diethyl sulfide comprise the index of odorous compounds on the working face of typical municipal solid waste landfill in China.Waste Management 01/2015; DOI:10.1016/j.wasman.2015.04.030 · 3.16 Impact Factor