Determination of absolute amount extracted by solid-phase microextraction: Different approaches under examination

Assessment of gas-phase concentrations of organophosphate flame retardants at the material surface using a midget emission cell coupled to solid-phase microextraction

Actual methods for on-site measurement of gaseous concentrations of Semi-Volatile Organic Compounds (SVOCs) at the material surface (y⁰) are not yet sufficiently developed mainly due to sampling difficulties. These concentrations are the key data to improve knowledge about indoor sources and human exposure to SVOCs. To the end, a specific emission cell coupled to solid-phase microextraction (SPME) was developed. The main challenge with this method is calibration because of very low volatility of SVOCs and static sampling mode. In this study, a generating system of organophosphate flame retardants (OFRs) using polyurethane foam as source combined with an active sampling method with Tenax tubes was proposed as a novel calibration device for SPME-based method. The generating system delivered stable OFR concentrations after 190 h of operation with a variation not exceeding ±5%. It allowed to obtain robust calibrations for tris-(2-chloropropyl)-phosphate (TCPP) and tri-butyl-phosphate (TBP) measured with the emission cell coupled to SPME-based method, define the optimal sampling requirements and achieve reproducible and accurate measurements of y⁰ at μg.m^-3 level. TCPP and TBP gas-phase concentrations at the polyurethane foam surface (y⁰) were followed up over more 228 days under controlled temperature conditions. A high stability of these concentrations was observed showing that polyurethane foam acts as a stable and continuous source of organophosphate flame retardants indoors. This novel method should be useful for assessing the dynamic of emissions from indoor sources and potential exposure to SVOCs in indoor environments.

Determination of the volatile fraction of phosphorus flame retardants in cushioning foam of upholstered furniture: towards respiratory exposure assessment

The purpose of this paper was to highlight potential exposure in indoor air to phosphorus flame retardants (PFRs) due to their use in upholstered furniture. For that, an analytical method of PFRs by headspace coupled to solid-phase micro-extraction (HS-SPME) was developed on cushioning foams in order to determine the PFRs' volatile fraction in the material. Tests on model foams proved the feasibility of the method. The average repeatability (RSD) is 6.3 % and the limits of detection range from 0.33 to 1.29 μg g(-1) of foam, depending on the PFRs. Results showed that some PFRs can actually be emitted in air, leading to a potential risk of exposure by inhalation. The volatile fraction can be high (up to 98 % of the total PFRs amount) and depends on the physicochemical properties of flame retardants, on the textural characteristics of the materials and on the temperature. The methodology developed for cushioning foams could be further applied to other types of materials and can be used to rate them according to their potential releases of phosphorus flame retardants.

Modelling of toluene solid-phase microextraction for indoor air sampling

Solid-phase microextraction (SPME) is a convenient and efficient sampling technique recently applied to indoor air analysis. We propose here a theoretical model of the adsorption kinetics of toluene on SPME fibre under static extraction conditions. We discuss the effects of sampling volume and initial concentration of analyte on the adsorption kinetics. This model is used to estimate the limits of detection taking into account operating conditions and to calculate theoretical calibration curves. Results of comparison with experimental data are encouraging: only 11% difference for calibration curves and 30% for the estimation of the limit of detection. On the basis of this kinetics model, the solid concentration gradient in the Carboxen coating was modelled with Fick's second law of diffusion in unsteady-state mass-transfer mode. Mass diffusion from the gas sample to the SPME fibre was also investigated. It was shown that diffusion is the limiting step of the mass-transfer process in the static mode. Thus, the model developed, allows a better understanding of adsorption on Carboxen fibre and in the future could be a useful tool for cheap and time-saving development of SPME methods and the estimation of sampling performance.

Comparison of two solid-phase microextraction methods for the quantitative analysis of VOCs in indoor air

Competitive adsorption on adsorptive solid-phase microextraction (SPME) fibres implies careful determination of operating conditions for reliable quantitative analysis of VOCs in indoor air. With this objective, two analytical approaches, involving non-equilibrium and equilibrium extraction, were compared. The average detection limit obtained for GC-MS analysis of nine VOCs by the equilibrium method is 0.2 microg m(-3), compared with 1.9 microg m(-3) with the non-equilibrium method. The effect of the relative humidity of the air on the calibration plots was studied, and shown to affect acetone adsorption only. Hence, the concentrations that can be accurately determined are up to 9 micromol m(-3). The methods were then applied to indoor air containing different concentrations of VOCs. The non-equilibrium method, involving short extraction time, can be used for detection of pollution peaks whereas equilibrium extraction is preferable for measurement of sub-microg m(-3) ground concentration levels.

New approach based on solid-phase microextraction to estimate polydimethylsiloxane fibre coating–water distribution coefficients for brominated flame retardants

A depletion solid-phase microextraction (SPME) method based on multiple SPME extraction was applied to estimate fibre coating-water distribution constants (Kfs) of brominated flame retardants. Several polybrominated diphenyl ethers (PBDEs) including compounds present in the commercial mixture "Pentamix", and two polybrominated biphenyls (PBBs) were considered as target analytes. One hundred-micrometer poly(dimethylsiloxane) (PDMS) coating fibre was selected to estimate partition coefficients. SPME kinetics studies at 25 and 100 degrees C were performed. Kfs values obtained at both temperatures for brominated flame retardants were compared with the corresponding octanol-water partition coefficients (Kow) values found in literature. A linear log-log relationship between Kow with Kfs was found. To the best of our knowledge, this is the first study where brominated flame retardants Kfs values are estimated.

Study of preservation of polydimethylsiloxane/Carboxen solid-phase microextraction fibres before and after sampling of volatile organic compounds in indoor air

Solid-phase microextraction (SPME) was applied to the on-site analysis of volatile organic compounds (VOCs) in indoor air. The compounds were at trace levels, which complicates analysis and also sample storage. Fibre storage before and after sampling was studied. Several tests were performed, and the best results were obtained for a home-made storage assembly. To avoid contamination by acetone and acetaldehyde, activated carbon was added in the storage housing. Under these conditions, fibres can be stored up to 2 days before use. After sampling, storage of 10 VOCs was evaluated by varying air relative humidity of the air. This parameter was shown to be insignificant for 3 storage days: recoveries for acetaldehyde and acetone were 149 and 176%, respectively, and ranged from 95 to 107% for the other VOCs investigated.

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.

Diffusion-based calibration for solid-phase microextraction of benzene, toluene, ethylbenzene, p-xylene and chlorobenzenes from aqueous samples

Short-term solid-phase microextraction (SPME) was performed to test a recently proposed semi-empirical model for the prediction of concentrations of analyte in water samples from the fibre-extracted mass without further calibration. The mass uptake rates obtained for benzene, toluene, ethylbenzene and p-xylene (BTEX) differ considerably from the before published, showing that interfibre comparability is a serious issue. The relative prediction errors are between -55% for benzene and +82% for p-dichlorobenzene under optimal conditions, i.e. they are by an order of magnitude higher than originally published. A sensitivity analysis shows the dominant influence of the estimated thickness of the diffusional boundary layer around the fibre on the concentration predicted. Empirical modification of the model equation for this parameter yields satisfactory results under the conditions tested for both BTEX and the selected chlorobenzenes.

Solid-phase microextraction fibre-water distribution constants of more hydrophobic organic compounds and their correlations with octanol-water partition coefficients

Fibre coating-water distribution constants (Kfw) of more hydrophobic chemicals were determined with six different solid-phase microextraction fibre types (including a polyoctylmethylsiloxane (C8) prototype) by fibre exposure to agitated large-volume water samples lasting several days. The results obtained are comparable with Kfw values obtained under dynamic conditions. Octanol-water partition coefficients (Kow) were measured with the mixture of distributing substances to examine log Kfw-log Kow relationships based on a consistent dataset. Kfw values obtained with liquid polymer fibre coatings correlate reasonably well with the hydrophobicity of the test compounds (with decreasing sensitivity in the following order: 7 microm polydimethylsiloxane (PDMS)>100 microm PDMS>C8>polyacrylate) whereas this is not the case with the PDMS-divinylbenzene (DVB) and Carbowax-DVB fibres, partially porous coatings which provide the highest Kfw values for all substances tested.

Development of a quantification method for the analysis of malodorous sulphur compounds in gaseous industrial effluents by solid-phase microextraction and gas chromatography-pulsed flame photometric detection

A quantification method for malodorous sulphur compounds in gaseous industrial effluents using solid-phase microextraction sampling followed by gas chromatography-pulsed flame photometric detection has been developed. A comparative study showed that polydimethylsiloxane-Carboxen fibre led to sufficient sensitivity to achieve the microg m(-3) human perception levels of the five analytes studied (hydrogen sulphide, methanethiol, ethanethiol, dimethyl sulphide, dimethyl disulphide). However, this coating is known to suffer from competitive adsorption, which may lead to inaccurate quantification. Therefore, external calibration can only be used under a limited range of concentrations, which were determined from Fick's diffusion law. This approach was tested on a real gaseous sample and compared with the standard addition method. Good correlations were found for ethanethiol, dimethyl sulphide and dimethyl disulphide. However, for more volatile sulphur compounds (i.e., hydrogen sulphide and methanethiol), the easy-to-use external calibration could not be applied and standard additions had to be performed for accurate quantification.

Dynamic versus static sampling for the quantitative analysis of volatile organic compounds in air with polydimethylsiloxane-carboxen solid-phase microextraction fibers

Polydimethylsiloxane-Carboxen solid-phase microextraction fibers are now well known to be very efficient trapping media for the analysis of volatile organic compound (VOC) traces in air. However, competitive adsorption, due to the nature of the coating, considerably limits analyte quantitation. In this contribution, different experimental conditions are investigated to achieve quantitative analysis. Static and dynamic sampling were compared for the analysis of 11 VOCs in a standard gaseous mixture at different extraction times (1, 5, 15 and 45 min). The same experiments were performed with four isolated compounds. Adsorption results from gas mixture and isolated compounds were compared and a common linear range (i.e., where quantitative analysis is conceivable) was determined. When sampling was in the dynamic mode, compounds with lower affinity for the coating showed a very narrow linear range, meaning that competition for adsorption was quickly discriminative. The same experiments in static mode allowed one to obtain wider linear ranges for all compounds, especially for lower-affinity compounds: for a 1 min sampling time, acetone showed a linear adsorption range from 3 to 60 microg m(-3) in the dynamic mode which extended from 5 to 300 microg m(-3) in the static mode.