Quality control in quantification of volatile organic compounds analysed by thermal desorption-gas chromatography-mass spectrometry. J Chromatogr A 1186:348-357

Research Group EnVOC, Department of Organic Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium.
Journal of Chromatography A (Impact Factor: 4.17). 05/2008; 1186(1-2):348-57. DOI: 10.1016/j.chroma.2007.11.036
Source: PubMed


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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Available from: Herman Van Langenhove, Jul 19, 2015
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    • "After conditioning and before sampling, sorbent tubes were loaded with a gaseous internal standard (Tol-d8), separately prepared by making a two-phase system. In short, 500 mL from the headspace of the two-phase system, corresponding to 10.7 ng Tol- d8, was loaded onto each sorbent tube by means of a home-made heated (50 C) injection system flushed with He (100 mL/min) (Demeestere et al., 2008). Before each analytical run, TD-GC-MS was calibrated and the relative sample response factors (RSRF), defined as the ratio of response factor of the compound (peak area/ng loaded on the tube) and the response factor of the internal standard, were calculated for each VOC. "
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    ABSTRACT: Volatile organic compounds (VOCs) represent an important class of air pollutants, however their concentration levels in developing countries have scarcely been reported in literature. Therefore, concentration levels of 60 VOCs were determined at 27 urban and industrial locations in seven different cities in Ethiopia, Vietnam, the Philippines and Bangladesh between 2011 and 2014. Active sampling using Tenax TA as a sorbent was employed followed by TD-GC-MS analysis using internal standard calibration. It was found that TVOCs concentration levels in Dhaka, Bangladesh (arithmetic mean: 343 and 399 μg/m3 for urban and industrial campaign, respectively) were more than 10 times higher when compared to TVOCs levels observed in Mekelle, Ethiopia. ∑BTEX concentration at street sites ranges from 36 μg/m3 in Mekelle, to 100 and 250 μg/m3 in Hanoi, Vietnam and Dhaka, Bangladesh, respectively. The indoor to outdoor concentration ratios were found to be dependent on the country, type of environment, VOC compound and outdoor reference location. The highest Ozone Formation Potential (OFP, 2150 μg/m3), calculated from the same set of seven aromatic VOCs, was obtained at the street site in Dhaka. This OFP value is a factor three and four times higher than the OFP value observed at the street sites in Hanoi, and Manila, respectively. Finally, the Cumulative Cancer Risk (CCR) calculated for four carcinogenic VOCs ranged from 97 × 10-6 in urban Mekelle to 299 × 10-6 in urban Dhaka. This work provides for the first time comparisons of CCR in urban and industrial environments in the selected developing countries.
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    • "This characterization is fundamental to further study on the mechanism of odorous gas formation and finally improve the operation of waste treatment system by controlling the odor formation and emissions. Efforts have been made during the last decades on qualitative and quantitative analysis of odorous compounds from different landfills, and Table 1 is the summary of these results (Brosseau and Heitz, 1994; Chiriac et al., 2007; Davoli et al., 2003; Deipser and Stegmann, 1994; Demeestere et al., 2008; Dincer et al., 2006; Fang et al., 2012). "
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    • "For the quantitative analysis of highly volatile compounds, preparation of standards is an important part of performing accurate quantification. For this purpose, the use of a gaseous standard is a common option, as it allows the elimination or suppression of major experimental drawbacks (e.g., the matrix effect) encountered due to the phase difference between the sample (gas) and the standard phases (liquid) [10] [11]. However, the storage of diverse volatiles in gas phase may be complicated as sample integrity can degrade with time [12]. "
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    ABSTRACT: In the analysis of biogenic volatile organic compounds (BVOCs) in ambient air, preparation of a sub-ppblevel standard is an important factor. This task is very challenging as most BVOCs (e.g., monoterpenes) arehighly volatile and reactive in nature. As a means to produce sub-ppb gaseous standards for BVOCs, weinvestigated the dynamic headspace (HS) extraction technique through which their vapors are generatedfrom a liquid standard (mixture of 10 BVOCs: (1) �-pinene, (2) �-pinene, (3) 3-carene, (4) myrcene, (5) �-phellandrene, (6) �-terpinene, (7) R-limonene, (8) �-terpinene, (9) p-cymene, and (10) Camphene) spikedinto a chamber-style impinger. The quantification of BVOCs was made by collection on multiple-bedsorbent tubes (STs) and subsequent analysis by thermal desorption–gas chromatography–mass spec-trometry (TD–GC–MS). Using this approach, sub-ppb level mixtures of gaseous BVOCs were generatedat different sweep cycles. The mean concentrations of 10 BVOCs generated from the most stable condi-tions (i.e., in the third sweep cycle) varied in the range of 0.37 ± 0.05 to 7.27 ± 0.86 ppb depending on theinitial concentration of liquid standard spiked into the system. The reproducibility of the gaseous BVOCsgenerated as mixture standards, if expressed in terms of relative standard error using the concentrationdatasets acquired under stable conditions, ranged from 1.64 (�-phellandrene) to 9.67% (R-limonene).
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