Fig. 9

a Dynamical response transients of S1, S2, S3, and S4 to methanol gas at low concentration at 195 °C. b Relationship between response and concentration of S1, S2, S3, and S4 to different methanol gas concentration (1 ppm, 2 ppm, 3 ppm, 4 ppm, and 5 ppm) at 195 °C