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: Apple volatiles emitted at early phenological stages are little investigated, although they may influence behavior of early-season pests. The apple blossom weevil Anthonomus pomorum is a herbivore pest of orchards in Europe. It colonizes apple trees in early season and oviposits into developing flower buds, often leading to economic damage. Using in situ radial diffusive sampling and thermal desorption, followed by GC/MS analysis, headspace volatiles from apple twigs with flower buds at three early phenological tree stages were identified and quantified. The volatile blend consisted of 13 compounds for the first, and increased to 15 compounds for the third phenological stage sampled. These blends included benzenoids, terpenes, and derivatives of fatty acids. A recombined synthetic blend served as the odor source in a still-air dual-choice olfactometer bioassay, in which individual male and female weevils were tested. Results from this behavioral test document an attraction of both sexes to odors of their host plant, suggesting that apple volatiles emitted in early season serve as olfactory cues for host location of A. pomorum in the field.Chemistry & Biodiversity 09/2010; 7(9):2254-60. · 1.81 Impact Factor
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ABSTRACT: A method for quantifying secondary organic aerosol compounds (SOA) and water soluble secondary organic aerosol compounds (WSOA) produced from photo-oxidation of complex mixtures of volatile organic compounds (VOCs) in smog chambers by gas chromatography/mass spectrometry (GC/MS) has been developed. This method employs a double extraction with water and methanol jointly to a double derivatization with N,O-bis (trimethylsilil) trifluoroacetamide (BSTFA) and O-(2,3,4,5,6)-pentafluorobenzyl-hydroxylamine hydrochloride (PFBHA) followed by an analysis performed by GC/MS. The analytical procedure complements other methodologies because it can analyze SOA and WSOA compounds simultaneously at trace levels. As application, the methodology was employed to quantify the organic composition of aerosols formed in a smog chamber as a result of photo-oxidation of two different mixtures of volatile organic compounds: an anthropogenic mixture and a biogenic mixture. The analytical method allowed us to quantify up to 17 SOA compounds at levels higher than 20ngm(-3) with reasonable recovery and a precision below 11%. Values found for applicability, selectivity, linearity, precision, recovery, detection limit, quantification limit and sensitivity demonstrated that the methodology can be satisfactorily applied to quantify SOA and WSOA.Talanta 03/2013; 106C:20-28. · 3.50 Impact Factor
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ABSTRACT: In most urban environments of developing countries air pollution is becoming a priority problem beside the already existing environmental challenges, lack of safe water supply and adequate sanitary facilities. Volatile Organic Compounds (VOCs) are an important group of air pollutants since they play a crucial role in atmospheric science. In this work, 34 VOCs were monitored at two different cities of Ethiopia that are influenced by traffic. The first sampling campaign was conducted in Jimma town on August 27th, 2010 and the second sampling campaign was conducted at the capital city of the country, Addis Ababa, on September 8th, 2010. In both cities, active sampling method was employed by means of sampling tubes filled with Tenax TA as the sorbent material. Sampling was done in 6 time intervals (8-8:30h, 10-10:30h, 12-12:30h, 14-14:30h, 16-16:30h and 18-18:30h). The analysis was done by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) using internal standard calibration. The urban air quality in two cities of the country was evaluated by making use of TVOCs, individual compound concentration and OFP (ozone formation potential). Maximum TVOCs concentration of Addis Ababa is about 3 times higher than Jimma. The OFP at Addis Ababa (596 μg/m3) is about 2.4 times higher than Jimma (252 μg/m3) site. The benzene levels are 6 to 38 times higher than WHO guideline value (1 μg/m3) and also the levels of ozone which are quantified by using MIR (maximum incremental reactivity) scale are, 2.5 to 6 times higher than the WHO recommendation level (100 μg/m3). Vehicle exhaust was found to be the most prominent source as was proven by the evaluation of diagnostic ratios (T/B, E/B and Xm,p/B) and correlation coefficients between aromatic hydrocarbon concentration levels. To the best of our knowledge, this kind of research is done for the first time in Ethiopia and results in new insights on concentration levels of 34 VOCs. Therefore, this study is expected to be helpful to the Environmental Protection Agencies in assessing and minimizing the adverse impact of toxic VOCs in urban air environment of the nation.06/2011, Degree: MSc, Supervisor: Prof. Dr. ir. H. Van Langenhove and Prof. Dr. ir. K. Demeestere