## 3 Results
Data obtained in the test were processed in the computer to obtain the calibration curve of the instrument, which was then implemented in the microcontroller. Using the exponential dilution system, the calibration curve was obtained by preparing air gas streams containing various concentrations of acetone that passed through the flow-cell containing the sol-gel sensing material, and the luminescent behavior was collected with the aid of the equipment and a software application made in National Instruments LabVIEW 2015. The quencher (acetone) concentration can be directly related to the luminescence intensity using the well-known Stern-Volmer equation:  
\[\frac{I_{0}}{I}=1+K_{sv}[Q], \tag{1}\]  
where \(I_{0}\) is the phosphorescence intensity of the luminescence of the QDs in the absence of the quencher, \(K_{sv}\) is the Stern-Volmer constant, [Q] is the analyte concentration in the gas stream, and \(I\) is the phosphorescence intensity in presence of the quencher. Figure 8a shows the phosphorescent response of the sensing phase to increasing the acetone concentrations in the air gas flow. This figure was obtained at the output of the PMT. The optimal synthetic air gas flow, providing a higher quenching effect for a given acetone concentration, was found to be 250 mL min\({}^{-1}\). At higher flow rates, the shorter interaction time between the passing acetone and the sol-gel sensor prevented an adequate quenching effect from taking place. As can be seen, the presence of acetone into the air stream interacted with the sensor by quenching or deactivating the signal emitted by the sensor material. This behavior is common in turn-off luminescent sensors that generate their maximum signal in the absence of analyte and the presence of contaminant causes deactivation of that signal. As can be seen, this is a reversible sensor system. The luminescence signal completely recovered to its initial value when the influence of the contaminant disappeared. This property is of great interest in portable applications since it is not necessary to change the sensing phase between analyses and continuous analyte monitoring can be performed. The dependence of the measured phosphorescent intensity signal with increasing concentrations of acetone was fitted to a Stern-Volmer equation (see Figure 8b), which describes the change in photoluminescence emission as a function of the added quencher. For this purpose, (Io/I) was plotted versus the acetone concentration, where Io is the phosphorescent emission of the sol-gel sensing material exposed to an airflow containing acetone  
Figure 7: Experimental setup used to characterize the analytical performance of the phosphorimeter. (**a**) Picture of the assembled instrumental prototype showing the system used to generate air samples with known acetone concentrations. (**b**) Diagram of the exponential dilutor chamber. and \(I\) is the phosphorescent emission of Mn:ZnS QDs in the presence of increasing concentrations of acetone. The response times, which were the result of the on-off cycling of 157 ppm acetone in gas media over the sensing phase, were found to be \(<3\) min (see Figure 9). As can be seen, after a fast decrease of the phosphorescence signal once the gaseous acetone arrived in the sensing phase, there was a small drift of the signal that was most probably caused by signal stabilization and kinetics of the interaction between acetone and the sol-gel doped with the QDs, as well as the beginning of the recovery of the signal as the acetone concentration in the airflow started to decrease according to an exponential dilution curve. Once the acetone concentration in the airstream was reduced, the phosphorescence signal completely recovered to the original one. Figure 8: (**a**) The phosphorescent response of the sensing phase to increases in acetone concentrations in the gas flow. (**b**) Calibration curve using the Stern–Volmer equation, which typically governs photoluminescence quenching processes.