Mesoporous silicate MCM-48 as an enrichment medium for ambient volatile organic compound analysis

This study investigated the sorption/desorption properties of MCM-48 and its applicability as a sorbent for on-line gas chromatographic analysis of ambient volatile organic compounds (VOCs). To establish a valid comparison, commercially available carbon sorbents were evaluated under similar analytical conditions. Two trapping temperatures of 30 degrees C and -20 degrees C, representing ambient and sub-ambient temperatures, were tested by trapping a full range of VOCs from C(2)-C(12). At ambient temperatures, due to the mesoporosity, the MCM-48 showed considerably limited trapping efficiency compared to microporous carbon sorbents on the highly volatile section of VOCs and only began to show effective trapping for compounds larger than C(7). Cooling to sub-ambient temperatures (e.g., -20 degrees C) extended the effective trapping down to C(4) VOCs, drastically increasing the applicability of MCM-48 as an in-line enrichment medium for gas chromatographic analysis of VOCs. The mesoporosity of MCM-48 also aided desorption. Much lower desorption temperatures (100-180 degrees C) were required for full desorption as compared to the temperatures (greater than 200 degrees C) required for carbon sorbents. Moreover, the easy desorption was accompanied by a low memory effect, as the large pores of MCM-48 can clean up more efficiently after desorption, with little residue left behind.