Pierre Mocho

Development of a solid phase microextraction (SPME) method for the sampling of VOC traces in indoor air

Solid-phase microextraction (SPME) was studied for the measurement of volatile organic compounds (VOCs) in indoor air. An adsorptive PDMS/Carboxen fibre was used and an analytical methodology was developed in order to overcome competitive adsorption. Kinetics and adsorption isotherms were investigated for different sample volumes and model compounds. In order to evaluate competitive adsorption on the fibre, these compounds were studied alone and in mixture. From the results obtained, the operating conditions allowing co-adsorption of the target compounds were determined: the air sample is enclosed in a 250 mL glass bulb where the SPME fibre is exposed until adsorption equilibrium. This procedure was combined with GC/MS analysis for the identification and quantification of VOCs in indoor air. The performances were determined by using a standard gas containing 10 VOCs representative of indoor environments (acetaldehyde, acetone, BTX, alpha-pinene, trichloroethylene, alkanes). The detection limits were determined in single ion monitoring mode and for a signal to noise ratio of 3. Except acetaldehyde (6 microg m(-3)), they are all below 0.5 microg m(-3). Calibration curves are linear up to 10 micromol m(-3) for all the compounds with good correlation coefficients (above 0.99). The reproducibility ranges from 6 to 12% according to the compound. The methodology was then applied to the comparison of the VOCs content in classrooms of two different schools.

Solid phase microextraction sampling for a rapid and simple on-site evaluation of volatile organic compounds emitted from building materials.

A new sampling method was developed for a simple and fast evaluation of volatile organic compounds (VOCs) emitted at trace levels from building materials. The device involves an emission cell coupled with solid phase microextraction (SPME) for diffusive sampling. Owing to possible competitive adsorption of VOCs onto the PDMS-Carboxen fiber used, the co-adsorption conditions were determined through kinetics study of isolated and in mixture compounds. Hence, the linear concentration ranges which ensure reliable quantification were determined from 4.8 to 10mgm(-3)min according to the VOC studied. Thus, the analyst can select the extraction time that fits for his best analytical objectives. For example, sub microgm(-3) limits of detection can be achieved for GC-MS analysis for 20min extraction. On the other hand, 5min sampling is sufficient for a rapid screening of the major emitted VOCs, since the average limit of quantification reaches 20microgm(-3) for GC-FID analysis.

Formaldehyde emission behavior of building materials: on-site measurements and modeling approach to predict indoor air pollution.

The purpose of this paper was to investigate formaldehyde emission behavior of building materials from on-site measurements of air phase concentration at material surface used as input data of a box model to estimate the indoor air pollution of a newly built classroom. The relevance of this approach was explored using CFD modeling. In this box model, the contribution of building materials to indoor air pollution was estimated with two parameters: the convective mass transfer coefficient in the material/air boundary layer and the on-site measurements of gas phase concentration at material surfaces. An experimental method based on an emission test chamber was developed to quantify this convective mass transfer coefficient. The on-site measurement of gas phase concentration at material surface was measured by coupling a home-made sampler to SPME. First results had shown an accurate estimation of indoor formaldehyde concentration in this classroom by using a simple box model.

Modelling of adsorption kinetics and calibration curves of gaseous volatile organic compounds with adsorptive solid-phase microextraction fibre: toluene and acetone for indoor air applications

Solid-phase microextraction (SPME) with adsorptive Carboxen/PDMS fibre is a powerful sampling device for volatile organic compounds (VOCs) at trace levels in air. However, owing to competitive adsorption, quantification remains a challenging task. In this area, a theoretical model, based on Fick’s laws and an extended Langmuir equation, is proposed to deal with the adsorption kinetics of acetone/toluene mixture on SPME fibre under various static extraction conditions. The semipredictive model is first used to determine the axial diffusion coefficients of analytes in the sampling device. The model is then tested with a complex VOC mixture, showing good agreement with experimental data.

Performance of the Radiello® diffusive sampler for formaldehyde measurement: the influence of exposure conditions and ozone interference

The radial diffusive standard sampler Radiello® filled with Florisil impregnated with 2,4-dinitrophenylhydrazine (DNPH) was evaluated with the goal of survey monitoring the formaldehyde concentration in indoor air for a 4.5 day sampling time. A Radiello® sampler provides measurements with a relative standard deviation of repeatability comprised between 1.5 and 4.0%, a high sampling rate assessed to 98.7 ± 2.8 mL min−1 under standard conditions (temperature: 19.9 ± 0.5 °C and relative humidity: 52.9 ± 3.2%) and a detection limit of 0.5 μg m−3 for a 4.5 day sampling time. The influence of three environmental factors (temperature (T°), relative humidity (RH) and ozone concentration (O3)) on the sampling rate was also evaluated in an exposure chamber following a fractional design of the experiment at two factor levels (low and high). Temperature is found to be the factor leading to the most significant variation of the sampling rate with an effect of +1.8% per °C. From the fractional design of the experiment, a model was set up for expressing the sample rate of Radiello® as a function of significant factors and the uncertainty on the sampling rate was assessed to 11.9% under the domain of tested conditions.

Static SPME sampling of VOCs emitted from indoor building materials: prediction of calibration curves of single compounds for two different emission cells

Solid-phase microextraction (SPME) is a powerful technique, easy to implement for on-site static sampling of indoor VOCs emitted by building materials. However, a major constraint lies in the establishment of calibration curves which requires complex generation of standard atmospheres. Thus, the purpose of this paper is to propose a model to predict adsorption kinetics (i.e., calibration curves) of four model VOCs. The model is based on Fick’s laws for the gas phase and on the equilibrium or the solid diffusion model for the adsorptive phase. Two samplers (the FLEC® and a home-made cylindrical emission cell), coupled to SPME for static sampling of material emissions, were studied. A good agreement between modeling and experimental data is observed and results show the influence of sampling rate on mass transfer mode in function of sample volume. The equilibrium model is adapted to quite large volume sampler (cylindrical cell) while the solid diffusion model is dedicated to small volume sampler (FLEC®). The limiting steps of mass transfer are the diffusion in gas phase for the cylindrical cell and the pore surface diffusion for the FLEC®. In the future, this modeling approach could be a useful tool for time-saving development of SPME to study building material emission in static mode sampling.

Using the chemical mass balance model to estimate VOC source contributions in newly built timber frame houses: a case study

Basing on the material emission data obtained in a test chamber, chemical mass balance (CMB) was used to assess the source apportionment of volatile organic compound (VOC) concentrations in three newly built timber frame houses. CMB has been proven to be able to discriminate the source contributions for two contrasted environmental conditions (with and without ventilation). The shutdown of the ventilation system caused an increase in the VOC concentrations due to the increased contribution of indoor surface materials like the door material and furniture explaining together over 65% of total VOCs. While the increase in formaldehyde concentration is mainly due to furniture (contribution of 70%), the increase in α-pinene concentration is almost exclusively attributable to the emission of door material (up to 84%). The apportionment of VOC source contributions appears as highly dependent on the position of source materials in the building (surface materials or internal materials) and the ventilation conditions explaining that the concentrations of compounds after the shutdown of ventilation system do not increase in equivalent proportion. Knowledge of indoor sources and its contributions in real conditions may help in the selection of materials and in the improvement of construction operations to reduce the indoor air pollution.