Diffusive sampling of methylene chloride with solid phase microextraction

This study examined the characteristics of a solid phase microextraction (SPME) assembly as a passive sampler to determine the short-term exposure level (STEL) of methylene chloride. Two types of SPME fibers and six sampling-related factors were chosen and nested in an L18 Taguchi's orthogonal array. Samples were thermally desorpted and analyzed by gas chromatograph equipped with an electron capture detector (GC/ECD). The use of 85-μm Carboxen/polydimethylsiloxane (Car/PDMS) fibers resulted in greater adsorbed mass, which was highly correlated with the product of concentration and sampling time (r > 0.99, p < 0.0001), than 85-μm polyacrylate fibers. The sampling rate (SR) of the 85-μm Carboxen/polydimethylsiloxane fibers was not significantly affected by variations in relative humidity (0–80%) and coexistent toluene (none to 100 ppm). Variance of sampling rate was predominantly attributed to the diffusive path length (86.4%) and sampling time (5.7%). With diffusive paths of 3, 10 and 15 mm, the sampling rates of 85-μm Carboxen/polydimethylsiloxane fibers for methylene chloride were 1.4 × 10−2, 7.7 × 10−3 and 5.1 × 10−3 mL min−1, respectively. The measured sampling rates were greater than the theoretical values, and decreased with increment of sampling time until they came to constant.