Table 1 Specification of all chemoresistive sensors used in the e-nose system.
Gas sensor | Sensor type | Main target analytes | Measurement range | Sensitivity (sensor resistance ratio change) | Limit of detection (LOD) (ppm) | Detectable gases (cross-sensitivity) |
|---|---|---|---|---|---|---|
S1 | MOS | Organic solvent vapors | 1 to 10 kΩ in ethanol at 300 ppm/air | 0.40 ± 0.10 | 50 | Acetone, benzene, carbon monoxide, ethanol, isobutane, methane, and n-hexane |
S2 | MOS | Isobutane methane, and propane | 1 to 25% lower explosive limits (LEL) of each gas | 0.50 to 0.65 | 300 | Butane, methane, and propane |
S3 | MOS | Alcohol and solvent vapors | 50 to 5000 ppm ethanol | 0.3 to 0.5 in ethanol | 50 | Alcohol and carbon monoxide |
S4 | MOS | Chlorofluorocarbons | 4 to 40 kΩ in 1,1,1,1-tetrafluoroethane (R-134a) at 100 ppm/air | 0.50 to 0.65 | 10 | Chlorofluorocarbon, ethanol, and hydrofluorocarbons |
S5 | MOS | Ammonia | 30 to 300 ppm | 0.55 ± 0.15 | 30 | Ammonia, ethanol, hydrogen, and isobutane |
S6 | MOS | Air contaminants (trimethylamine and methyl mercaptan) | 1 to 100 ppm ethanol | <0.5 | 0.3 | Ethanol, hydrogen, hydrogen sulfide, methyl mercaptan, and trimethylamine |
S7 | MOS | Air contaminants (hydrogen and ethanol) | 1 to 30 ppm of H2 | 0.3 to 0.6 | 1 | Carbon monoxide, ethanol, hydrogen, isobutane, and methane |
S8 | MOS | Combustible gases | 5 to 15 kΩ in methane at 1000 ppm/air | 0.6 ± 0.05 | 500 | Carbon monoxide, ethanol, hydrogen, isobutane, methane, and propane |
