The use of multi-channel silicone rubber traps as denuders for polycyclic aromatic hydrocarbons

Department of Chemistry, Faculty of Natural and Agricultural Sciences, University of Pretoria, South Africa.
Analytica chimica acta (Impact Factor: 4.51). 06/2012; 730:71-9. DOI: 10.1016/j.aca.2011.11.013
Source: PubMed


Atmospheric polycyclic aromatic hydrocarbons are ubiquitous environmental pollutants, which may be present both in the gaseous phase and adsorbed onto the surface of particles. Denuders are sampling devices which have been effectively employed in such partitioning applications. Here we describe and characterise a novel miniature denuder consisting of two multi-channel silicone rubber traps (each 178 mm long, 6 mm o.d. containing 22 silicone tubes), separated by a quartz fibre filter for particle phase collection. The denuder only requires a small portable personal sampling pump to provide sampling flow rates of ∼0.5 L min(-1). Theoretical considerations indicated that the air flow through the denuder was expected to be laminar, and the linear velocity arising from longitudinal diffusion was found to be negligible. The calculated particle transmission efficiency through the denuder was found to be essentially 100% for particles>50 nm, whilst the experimental overall efficiency, as determined by CPC and SMPS measurements, was 92 ± 4%. The size resolved transmission efficiency was <60% for particles below 20 nm and 100% for particles larger than 200 nm. Losses could have been due to diffusion and electrostatic effects. Semi-volatile gaseous analytes are pre-concentrated in the silicone of the trap and may be thermally desorbed using a commercially available desorber, allowing for total transfer and detection of the collected analytes by GC-MS. This enhances detection limits and allows for lower sampling flow rates and shorter sampling times, which are advantageous for studies requiring high temporal resolution.

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Available from: Patricia B C Forbes, Jul 21, 2014
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    • "Da Gasmoleküle im Vergleich zu Partikeln einen hohen Diffusionskoeffizienten aufweisen, werden diese beim Durchströmen des Denuders rasch an der Innenwand sorbiert (radiale Diffusion), während die Partikel den Denuder passieren. Ein nach dem Denuder angebrachter Filter kann diese sammeln, wobei eine Adsorberkartusche oder ein weiterer Denuder hinter dem Filter wiederum zur Aufnahme von desorbierten sowie vom Denuder nicht aufgenommenen Gasmolekülen dient [11]. An schließend kann das vom Denuder aufgenommene Gas nach der Probenahme extrahiert und separat analysiert werden [12]. "
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    ABSTRACT: Zusammenfassung Beim Einsatz von semi-volatilen organischen Sub-stanzen (SVOC) am Arbeitsplatz soll zur Bewertung des Gesundheits-risikos zwischen Gas-und Partikelphase unterschieden und somit sollen beide Phasen einzeln beprobt werden. Ein Denuder ist in der Lage, die Gas-von der Partikelphase zu trennen, wobei das vom Denuder aufge-nommene Gas nach der Probenahme extrahiert und separat analysiert werden kann. In dieser Studie wurden Multichannel-PDMS-Denuder (MCD) im Hinblick auf ihre Transmissions-und Sorptionseffizienz für Partikel bzw. Gasphasenkomponenten untersucht. Die Transmissions-effizienz wurde mit Polystyrol-Latex(PSL)-Partikeln der Größen 0,3, 0,51, 0,75, 0,99, 1,54 und 1,93 mm bestimmt. Dabei konnte eine größenabhängige Transmissionseffizienz von 93,3 bis 86,7 % für Ther-modesorptionsröhrchen (TD) mit einem Innendurchmesser (ID) von 4 mm (22 Polydi methylsiloxan(PDMS)-Schläuche) und eine Transmissions effizienz von 91,6 bis 73,0 % für TD mit einem ID von 3,29 mm (16 PDMS-Schläuche) ermittelt werden. Die Versuche zur Be-stimmung der Sorp tionseffizienz ergaben für die MCD unter Gebrauch von un polarem n-Hexadecan eine wesentlich höhere Aufnahmefähig-keit (97 % nach 5 h, 85 % nach 24 h) als bei polarem Diethylenglycol (94 % nach 15 min, 49 % nach 135 min). Dadurch zeigte sich für n-Hexadecan ein ca. 30-fach größeres Durchbruchsvolumen. Abstract During the determination of hazardous occupational aerosols from semi-volatile organic compounds (SVOCs), it is important to measure both particle and gas phase. A denuder is able to separate the gas from the particle phase of an aerosol, and the collected gas can be extracted and analysed independently. In this study Multichannel-PDMS-Denuders (MCD) were analysed with respect to their transmission and collection efficiency. The transmission efficiency was determined with polystyrene latex(PSL)-particles with a size of 0.3, 0.51, 0.75, 0.99, 1.54 and 1.93 mm. Particle size-dependent transmission efficiencies be tween 93.3 to 86.7% for the 4 mm ID (inner diameter) liners (22 polydimethylsiloxane (PDMS) tubes) and 91.6 to 73.0% for the 3.29 mm ID liners (16 PDMS tubes) were measured. The experiments for the determination of the collection efficiency of MCD yielded for non-polar n-hexadecane a much higher sorption capacity (97% after 5 h, 85% after 24 h) than for polar diethylene glycol (94% after 15 min, 49% after 135 min). As a consequence, an approximately 30 times higher breakthrough volume was observed for n-hexadecane.
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    • "Multi-channel PDMS traps and thermal desorption in a commercial system were successfully used for monitoring of atmospheric polycyclic aromatic hydrocarbons (PAHs) [18] [22] [23] [24]. Advantages of the multi-channel PDMS trap over commercial packed or coated sorptive devices are its open tubular structure and low pressure drop associated with laminar multi-channel flow [21] [22] [24]. Compared to multi-channel traps consisting of a bundle of GC capillary columns which contain nonsorptive outer coatings, both the inside and the outside of the multi-channel silicone rubber trap provide sorptive surfaces. "
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