Using mesoporous silica MCM-41 for in-line enrichment of atmospheric volatile organic compounds

A mesoporous silica MCM-41 with pore size of 29 Å was synthesized and assessed for its applicability as a sorbent for in-line trapping of volatile organic compounds (VOCs) from air samples. Several commercially available microporous carbon molecular sieves, i.e., Carbosieve SIII, Carboxen 1000, Carboxen 1003, and Carbotrap purchased from Supelco, were employed to form either single sorbent traps or multi-sorbent traps for comparing adsorption properties with those of the silica MCM-41. A standard gas mixture containing more than 50 target compounds with size varying from C2 to C12 was adsorbed by these sorbents and the per carbon response of flame ionization detection (FID) for the target compounds was calculated for obtaining the adsorption profiles. While the multi-carbon sorbents show very uniform adsorption ability across the entire carbon range from C3 to C12, the mesoporous silica MCM-41, however, shows little sorption for smaller molecules from C3 to C7, but exhibit comparable sorption ability for C8–C12 compounds. Desorption at various temperatures indicates that C8–C12 compounds once trapped can be easily released at moderate temperatures of about 150 °C, whereas for carbon sorbents the desorption temperatures for sufficient recovery need to go beyond 300 °C due to much tighter hold-up in the microporous structure. Sorption ability for MCM-41 is also reflected on linearity. Compounds with sufficient sorption as suggested by the adequate per carbon response also exhibit excellent precision and linearity with R2 close to unity, an important requirement for quantitative analysis of ambient VOCs.