## 2 Results and Discussion
### Sensitivity Profile Established from Fresh and Dried Herbs  
This sensitive and selective e-nose was used for online monitoring of fresh and dried rosmary, basil and sage. For fresh herbs each measurement was continued for 5-7 days, whereas for dried ones it took three days. The time of each measurement depended upon the abundance of terpen recorded by headspace GC-MS analysis. Figure 4 shows the sensitivity profile of some original data on terpen emanated from fresh rosmary; the \"on-line\" monitoring was performed via 10 MHz QCM. The responses of two sensors were chosen which were templated with \(\beta\)-pinene and \(\alpha\)-pinene, respectively. It is observed that each sensor shows a characteristic response depending on the template molecule. Figure 3: Selectivity profile of e-nose at 50 ppm. Imprinting e.g., with \(\beta\)-pinene yields frequency shifts by more than a factor of two compared to \(\alpha\)-pinene. After a stable baseline was established a constant vapor pressure of rosemary emanations was reached, and the frequency shift is lowered by \(\leq\)2,800 Hz and \(\leq\)700 Hz for the layers. Thus, a stable sensor behavior was observed for several hours, leading to a highly reproducible sensor signal at the end point. Sometimes minute fluctuations of sensor responses were monitored, depending upon temperature changes which can be eliminated by differential measurements. A similar trend was observed for all fresh and dried herbs. During online monitoring, small humidity effects of \(\leq\)40-60 Hz were observed, which are negligible in comparison to actual signals of fresh rosemary. Former investigations had revealed similar humidity cross sensitivities, when copolymers based on styrene/divinylbenzene were used [18]. Additional improvements resulted from a QCM coated with polyvinyl alcohol, which show strong hydrophilic properties. Thus, a nearly selective humidity sensor is available, which can be used for taking into account variations of ambient surroundings. In Figure 5 emanation patterns of terpen from all fresh and dried herbs considered as a function of time are shown. The data generated by sensor array measurements shows an obvious difference between terpen emanated from fresh and dried herbs as high responses of \(\alpha\)-pinene of 310-950 Hz and 110-176 Hz from fresh and dried herbs were observed respectively. The second major contribution of limonene and eucalypt _i.e._, 250-350 Hz from fresh and 70-120 Hz from dried herbs was observed. Figure 4: Emanation from fresh rosemary by MIP layers imprinted with \(\alpha\)-pinene and \(\beta\)-pinene. A third major pattern was obtained from terpinene and estragole _i.e._, 100-132 Hz from fresh and 23-33 Hz from dried herbs. The lowest amounts \(\leq\)44 Hz and \(\leq\)12 Hz of \(\beta\)-pinene have been observed from all the fresh and dried herbs respectively. These responses basically correspond to the amount of terpen emanated from the herbs. As the measurement proceeded further these responses  
Figure 5: Terpene emanation patterns from fresh and dried herbs. decreased towards lower values in the same fashion. The most innovative feature of the sensor array is the achievement of sensitivity and selectivity for real time and online monitoring of emanated terpen under ambient conditions efficiently and quickly. Furthermore it is sensitive enough to distinguish between isomers of a compound like \(\alpha\)-pinene and \(\beta\)-pinene. A linear behavior is observed between the sensor signals and the amounts of emanates and each layer is responding differently towards its analyte _i.e._, greater the amount of analyte, higher the signal and _vice versa_. This behavior can be explained by the mass sensing nature of the transducer and structural properties of analytes. Four isomers of terpene family _i.e._, \(\alpha\)-pinene, \(\beta\)-pinene, limonene and terpinene have similar molar masses and formulas.