Evaluation of the effect of the storage time on the sensitivity of SOx–SPCTTFEs. Calibration curves recorded in the sulfite concentration range from 5.9 to 51.2 μM, under the optimum conditions, using four different SOx–SPCTTFEs. (×) Calibration curve recorded the day that the biosensor was built, (lozenge, filled) calibration curve recorded one month after, (*) calibration curve recorded 2 months after, (●) calibration curve recorded 3 months after.