Detection of Nonpolar Vapors on Quartz Crystal Microbalances with Ni(SCN)2(4-picoline)4 Coatings

QCMs are spin-coated with films of Ni(SCN)2(4-picoline)4 and tested for their response to vapors of benzene, toluene, the three xylene isomers, styrene, n-heptane, cyclohexane, carbon tetrachloride, trichloroethylene, and 1,2-dichloroethane. The Ni(SCN)2(4-picoline)4 films exhibit rapid absorption and desorption of the less bulky molecules, especially the planar ones. Partition coefficients obtained from linear regions of calibration curves (frequency change vs vapor concentration) are in some cases above 105, more than 2 orders of magnitude higher than partition coefficients obtained with poly(isobutylene) films. Limits of detection in the ppb range are possible, especially for the xylenes, styrene, and trichloroethylene. The films lose both their sensitivity and their mass over a period of days. The vapor absorption mechanism appears to be clathration, with the analytes becoming guests in the host crystal lattice of Ni(SCN)2(4-picoline)4.