An Evaluation of a New Desorption Technique for Air Sampling Sorbent Tubes

Abstract

Air sampling sorbent tubes have been used for many years in determining concentrations of chemicals in the work environment. The conventional way to desorb analytes from the sorbents involves physical removal and transfer of the sorbent from the tube to a vial containing desorption solution. A new desorption technique, whole tube desorption--which involves adding the glass tube containing the sorbent to the vial containing the desorption solvents--has been evaluated. With this technique there is no transfer of sorbent out of the glass tube. Recovery efficiencies for several chemicals including ethylene oxide, methylene chloride and styrene were comparable to those obtained using traditional solvent desorption procedures. The utilization of this new desorption technique will involve a simple modification in the design of commercially available sorbent tubes so that the front and back sections can be physically separated. This new technique allows for a significant reduction in the time spent in the desorption of air sampling sorbent tubes and easier adaptation to laboratory robotic systems.

The Recovery of Volatile Organic Compounds and Volatile Sulfur Compounds in Fused-Silica Lined Canisters, Polyvinyl Fluoride/Tedlar Bags, and Foil-Lined Bags

“…Observed TICs included acetonitrile, 1-C9 hydrocarbon alkane, and 5-C12 hydrocarbon alkanes. Manufacturer disclaimers for PVF bags list possible phenol or dimethylacetamide contamination, but these were not observed in this study . The TIC acetonitrile was found in all of the PVF bags on day 0 at concentrations between 10 and 40 ppb.…”

“…Findings from this study aligned with previous critiques of a longer holding times, with recoveries of methylene chloride, propylene, tetrahydrofuran, trichloroethene, and toluene falling within ±5% on day 6 in Coyne et al’s study. However, benzene, 2-butanone, ethyl acetate, and i -propyl alcohol showed recovery differences of 14–24% in this evaluation over the same study time . The recovery differences are thought to be due to the significantly lower VOC concentrations or possible effects due to humidity.…”

“…PVF bags are commonly used because of their convenience and relatively low cost, but previous evaluations have found conflicting and limited information on the stability of VOCs and VSCs stored in these containers. − VOC and VSC storage stability are of particular concern, with two prominent manufacturers of PVF and foil-lined bags, SKC Inc., and Restek, suggesting a maximum holding time of 2 days for a limited number of VOCs and VSCs. , Many studies have stopped collecting data, while VOC and VSC recoveries were still within acceptable limits, which limits understanding of the true length of an appropriate holding time. − Coyne et al (2011), for example, evaluated PVF bags prepared with 32 VOCs and ended the study after 2 days, even though most of the VOCs under review remained well above acceptable recovery limits (>90%). , Kim et al (2011) found similar results when studying a range of VOC recoveries collected in PVF bags over 3 days, also finding sufficient recoveries (>90%) on day 2 for all but two VOCs ( p -xylene and styrene), which coincided with other findings. − It has been theorized that a high concentration of VOCs will “fill” active sites on the PVF bag surface and reduce observable VOC recovery issues, which therefore raises questions regarding the stability of VOCs and VSCs at lower and more practical concentrations. , …”

“…These findings bring into question the influence of theorized active-sites and suggests that stability might be more related to the mass transfer of VOCs with the PVF material. A few studies have conducted extended evaluations with mixed success, one notable example being Coyne’s (2010) evaluation of the stability of VOCs over 6 days, which found that higher boiling point and polar compounds (e.g., methylene chloride, tetrahydrofuran, toluene) were observed to have considerable losses (75.5–88.9%) by day 6, while lower boiling point VOCs recovered at >94% on day 6 …”

“…Foil-lined bags are known to have a high concentration of VOC contamination (100s of ppb) and are not recommended for VOC collection. , One study of SKC Inc.’s proprietary foil-lined bags, known as “Flexfoil plus” bags, showed background contamination of 11–13 ppb of the carbonyl sulfide, which raises the question of similar contamination issues with their use. Generally, evaluations of VSCs in foil-lined bags have been minimal and the work that has been done shows a low recovery of many VSCs. ,,, One evaluation of foil-lined bags by Coyne et al (2011) found that among 20 VSCs, only hydrogen sulfide, carbonyl sulfide, methyl mercaptan, ethyl mercaptan, i-propyl mercaptan, and t-butyl mercaptan were recovered >90% on day 1 and 2 of the study . The suggested holding time has also been questioned, with Mochalski et al.…”