Fixation of XAD-4 power on filter paper using methyl cellulose for the passive air sampling of semi-volatile organic compounds in indoor air

The sorption capacity of a substrate serving as sampling medium can be enhanced by adding another sorbent to its surface. This is usually achieved through an impregnation process by repeated dipping of the substrate in a slurry solution containing the powder of the sorbent. Because the impregnation process only deposits the sorbent powder on the surface of the substrate, the powder could detach and fall off during field deployment. In this study, a novel approach was explored to fix the added sorbent powder to the surface of the substrate. Methylcellulose (MC) in fine crystal form was selected as the fixing agent to secure the powder of polystyrene-divinyl benzene copolymer resin (XAD-4), with its high sorption capacity, to a cellulose filter paper (CFP). The process involved first mixing XAD-4 and MC in the presence of water to form a milky slurry solution that was then painted on to the surface of the paper and then allowed to dry. The painting technique resulted in a good reproducibility of the applied amount of XAD-MC mixture with a relative standard deviation (RSD) of 12% (n = 5). Scanning electron microscope (SEM) images showed that the XAD-4 powder was held to the surface of the filter paper. No free XAD powder was dislodged from the coated filter paper when coated paper was flicked with a finger. For use as an indoor passive air sampler (PAS), this new sampling medium was placed in a round housing made of electronically polished aluminium material and was tested for uptake of polybrominated diphenyl ethers and phthalic acid dialkylesters. Surface area specific uptake rates (ASUR) of PBDEs ranged from 1.14 to 2.82 m³/(dm²d), while ASUR of phthalates had a wider range from 2.74 to 5.66 m³/(dm²d).