The solid-phase microextraction (SPME) technique has been utilized as a solvent-free sampling and analytic method. Polydimethylsiloxane (PDMS) has been known as an excellent material for the extraction of volatile organic compounds (VOCs). The object of this study was to investigate the adsorption kinetics of benzene and toluene onto SPME/PDMS membranes. Adsorption curve of PDMS in the benzene and toluene gaseous sample were obtained using individual batch experiments. Base on a one-dimensional Fick’s diffusion equation, the diffusion and partition coefficients of benzene and toluene in SPME/PDMS were determined.
The individual adsorption experiments were conducted for 1~300 seconds. After extraction from 5.05 ml benzene and toluene gas samples, the SPME/PDMS fiber was introduced into GC/FID. The extraction temperature was kept at 25±0.5oC. The injector temperature was 220oC. The detector temperature was 250oC. The experimental variables were concentrations and concentration ratio of gas sample.
The diffusion coefficients of benzene and toluene in SPME/PDMS single gas samples were 1.04?b0.11 (10-6 cm2/s) and 4.39?b0.75 (10-7 cm2/s), respectively. The partition constants of benzene and toluene in single gas samples were 794?b122 and 1947?b175, respectively. By way of Correlation analysis, the diffusion and partition coefficients were not significantly correlated with the concentrations (p>0.05).
The diffusion coefficients of benzene and toluene in SPME/PDMS mixed gas samples were 4.00?b0.36 (10-7 cm2/s) and 2.50?b0.31 (10-7 cm2/s), respectively. The partition constants of benzene and toluene in mixed gas samples were 832?b93 and 1933?b149, respectively. By way of Correlation analysis the diffusion coefficients and partition constant were not significantly correlated with the concentrations (p>0.05).
This study indicated that there were statistically significant difference between diffusion coefficients of the single and mixed gas samples (p<0.05) and the there were no statistically significant difference between partition constant of the single and mixed gas samples (p>0.05). This study will serve as the fundamental work on the mass transfer of VOCs in PDMS, particular for SPME.
