Low-flow active and passive sampling of VOCs using thermal desorption tubes: theory and application at an offset printing facility

Abstract

While air sampling techniques using adsorbent-based collection, thermal desorption and chromatographic analysis have found a niche in ambient air sampling, occupational applications have been more limited. This paper evaluates the use of thermal desorption techniques for low flow active and passive sampling configurations which allow conveniently long duration sampling in occupational settings and other high concentration environments. The use of an orifice enables flows as low as 0.5 ml min(-1) and sampling periods up to several days without significant biases. A model is used to predict sampling rates of a passive sampler encompassing an orifice, a void space, glass wool, and the adsorbent. Laboratory and field tests conducted at a commercial offset printing facility, which contained a variety of volatile organic compounds (primarily aromatic but also a few chlorinated and terpene compounds at levels from 1 to 67,000 microg m(-3)), are used to evaluate the approach. Tenax GR and Carbosieve SIII, both singly and together, were employed as adsorbents. Side-by-side tests comparing high flow, low flow and passive samplers show excellent agreement and high linearity (r = 0.95) for concentrations spanning nearly five orders of magnitude. Active samplers were tested at flows as low as 0.5 ml min(-1), compared to typical flows up to 40 ml min(-1). Passive samplers demonstrated a linear range and agreement with predictions for adsorbate loadings from approximately 1 ng to nearly 10 microg. Using a chemical mass balance receptor model, concentrations in the facility were apportioned to solvents, inks and other indoor and outdoor sources. Overall, the use of low flow active and passive sampling approaches employing thermal desorption techniques provides good performance and tremendous flexibility that facilitates use in many applications, including workplace settings.

Evaluation of the use of Low Flow Passive Sampling Technique in Offset Printing Plants

“…This is probably due to limitations in the sensitivity of the traditional method at the relatively low concentrations investigated. Similar conclusions were also made by Batterman et al [1]. The samples collected by workers showed concentrations of the same order of magnitude as determined by the researchers.…”

“…In the USA, aromatic hydrocarbons are often used as cleaning solvents in offset printing [2]. This was also the case in the plant studied in Michigan, USA [1]. The use of glycol ethers and chlorinated hydrocarbons has also been reported [3].…”

“…This risk is smaller for diffusion tubes. Low-flow passive sampling with thermal desorption tubes was found to allow convenient long-term sampling at an offset printing facility in Michigan [1]. The method was demonstrated to be capable of sampling compounds with concentrations spanning nearly five orders of magnitude.…”

Diffusive Uptake Rates of Volatile Organic Compounds on Standard ATD Tubes for Environmental and Workplace Applications

“…Previous work developed Freundlich isotherm models [47,48], multilayer saturation models [12,49] and several computer programs [50,51]. However, the complexity and unavailability of parameters or programs impede the easy adoption of these models.…”

Porous silica spheres as indoor air pollutant scavengers

“…There have also been several studies using either metal or functionalised mesoporous materials for the removal of VOCs. There are a variety of techniques available for sampling of indoor air pollutants and these can be classified into three main categories: (i) active sampling, which is based on the controlled passing of a gas through a suitable cartridge or container filled with an adsorbent; 17,18 the desired components of the gas are retained in the container due to chemical or physical adsorption, (ii) passive sampling, which is based on the free flow of analyte molecules from a sampling medium to a collecting medium; devices are usually cartridge like in design and based on diffusion through a well defined barrier, [19][20][21][22] and (iii) denudation sampling which is a combination of active sampling where the gas is forced through a tube and the diffusion of analytes from the gas to the surface of the tube coated with a suitable adsorbent. 23,24 A more detailed description of denuder sampling devices is presented below.…”