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Determination of BTEX in air by SPME/GC/MS: standard gas mixtures production methods for the calibration
S. Tumbiolo, L. Vincent, J.-F. Gal, P.-C. Maria,a O. Zerbinati b
aUniversité de Nice-Sophia Antipolis, Faculté des Sciences, Chimie des Matériaux Organiques et Métalliques, Parc Valrose, 06108 Nice Cedex 2, France
Téléphone : +33(0)492076110 – Fax : +33(0)492076111 – E-mail : firstname.lastname@example.org
bUniversità del Piemonte Orientale « Amedeo Avogadro », Dipartimento di Scienze e Tecnologie Avanzate, Spalto Marengo 33/35, 15100 Alessandria, Italia
BTEX (benzene, toluene, ethylbenzene and xylenes) are volatile aromatic hydrocarbons with toxic properties. Exposure to BTEX can cause neurological, respiratory, genetic and excretory system damage. Analysis of BTEX results from the need for quality assurance of solvent/reactants and environmental applications to quantify BTEX contaminated air, soil and water samples. Gas-phase reactions of volatile organic compounds (VOCs) associated with photochemical oxidant cycles have been of great interest in predicting ozone (O3) concentrations and, more recently, secondary organic aerosol formation. The development of new methods like Solid Phase Microextraction (SPME) capable of rapid, sensitive and selective analysis of VOCs in complex matrices, such as ambient air, has important applications ranging from general screenings to accurate monitoring of controlled sites with the possibility of detailed temporary and spatial VOCs sources individuation . There is a main problem in getting this methodology ready: the production of, with a standard gas generation system, SPME calibration curves at trace concentrations . The experiences show that it’s very difficult to obtain BTEX’s standards gas mixtures at concentrations of ng/L levels, generated by static dilution. In these conditions, BTEX compounds were adsorbed on experimental walls of glassware. To obtain the interesting concentrations, we have studied two dynamics techniques : direct mechanic dilution and permeation tubes. The first technique allows to obtain concentrations from 1 to 100 mg/m3: two dilution steps of air flow polluted with BTEX compounds that have cylinder origin. The flows are controlled by high precision flowmeters. The second technique uses permeation tubes as a source of BTEX: each tube contains one pure compound and low concentrations are obtained diluting the analyte vapour in a air synthetic flow. We are studying the use of thermogravimetry as a means to measure rapidly the continuous weight-loss of tubes at constant temperature. A thermo balance SETARAM TG 92-12 with isothermic programming has been used for this study. Low permeation rate is calculated starting from the slope of mass-time relation. In 22,3 to 35,4 ng/min ranges of permeation rate, day-to-day variations of less than 5% were observed. Small tube volume minimizes the effects of possible changes due to Archimede’s push, coming from pressure and temperature daily fluctuations. Temperature regulation, with a stability of ±0,2°C, seems to be an important precision limiting factor . The potential of Solid Phase Microextraction for sampling VOCs in air at mg/m3 concentrations was investigated. Target compounds (benzene, toluene, ethylbenzene and xylenes) were extracted using SPME with a Carboxen/poly(dimethylsiloxane) fiber coating (extraction time = 30 minutes), and analysis was effectued by GC/MS. Linear calibration curves were obtained for BTEX concentrations from 0 to 50 mg/m3. Limits of detection, limits of quantification and repeatability were estimated. We thank ADEME (Agence de l’Environnement et de la Maîtrise de l’Energie), QUALITAIR (association nominate to the « Ministère de l’Environnement et du Développement Durable » at the control of air quality of Alpes Maritimes, Alpes de Haute Provence and Hautes Alpes departments), LENCA (Laboratoire de l’Environnement Nice – Côte d’Azur) and the « Conseil Général des Alpes Maritimes » for their participation in this projet.
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