title: Thermogravimetric calibration of permeation tubes used for the preparation of gas standards for air pollution analysis.
abstract: Sources of VOC (Volatile Organic Compounds) reference-materials at ppm and ppb levels are needed for calibration of air monitoring instruments. The permeation-tube technique is considered effective for the preparation of low concentration standards of high accuracy and stability. In this work, purpose-built PTFE permeation tubes, containing benzene, toluene, ethylbenzene, o-xylene or m-xylene (BTEX) were accurately and rapidly calibrated. Using the sensitive thermo-balance of a thermogravimetric apparatus, very low permeation rates were determined by the continuous monitoring of the tube weight loss as a function of time. Permeation rates in the range from 25 to 350 ng min(-1) were determined with precision. Thermogravimetry appears to be a rapid method for the measurement of weight loss at constant temperature, allowing rapid characterization and recalibration of permeation tubes. A detailed study on toluene, chosen as a typical case, showed that there are variations of the permeation rate in the long term. The temperature dependence of the permeation coefficient was also explored and permeation rates were shown to display an Arrhenius behavior in the temperature range 304-324 K. Thermodynamic parameters influencing the permeation were discussed.
authors.affiliation: Laboratoire de Radiochimie, Sciences Analytiques et Environnement, Faculté des Sciences, Université de Nice-Sophia Antipolis, Parc Valrose, 06108 Nice Cedex 2, France.
authors.forename: Simonetta
authors.initials: S
authors.lastname: Tumbiolo
authors.forename: Luc
authors.initials: L
authors.lastname: Vincent
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Gal
authors.forename: Pierre-Charles
authors.initials: PC
authors.lastname: Maria
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D002138:Calibration; D004784:Environmental Monitoring / Q000295:instrumentation* / Q000379:methods; D006112:Gravitation; D013696:Temperature
chemical_list: D000393:Air Pollutants