Sensors 2026 , 26 , 2049
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Each A4 office paper sheet was cut with a circular cutter (3.5 cm diameter), yielding 24 circles per sheet. Circles were placed in a clean Petri dish measuring 5 cm in diameter and kept with the lid on in a controlled environment. The temperature was set to 23 ◦ C, and the relative humidity (RH) was set to 35% and maintained for at least 24 h before sampling. Sampling for the sensor analytical system was manual. A chosen number of circles of each sample to be analyzed (22 were used in the analysis after an optimization process) were then placed inside a closed, homemade glass sampling chamber, as shown in Figure 1.
Figure1. SPME extraction: homemade glass sampling chamber with a paper sample.
An acrylic desiccator cabinet (Thermo Fisher Nalgene 5371-0180, Waltham, MA USA), equipped with a digital thermometer and humidity reader, was used for housing the glass sampling chamber during SPME sampling to maintain the humidity control after transferring samples from the climatized room to the laboratory sensor room. The SPME fiber, while retracted into the needle holder, was inserted through the Teflon septum on top of the glass sampling chamber. Afterwards, the fiber was exposed to the sample’s headspace. The exposure time was carefully controlled and, at the end, the SPME fiber was retracted again into the needle holder, removed from the sampling chamber, and inserted into the septum of a clean, closed vial to prevent contamination from the environment during transportation. For GC-TOF-MS analyses, an autosampler was used. The incubation time was 5 min, the temperature was 40 ◦ C, and the agitation velocity was 250 rpm; the desorption time was 4 min, and the temperature (inlet) was 200 ◦ C. 2.5. High-Resolution Gas Chromatography–Mass Spectrometry (HRGCTOF-MS) The separations were performed using a fused silica capillary column: SLB-5 ms (Supelco, Bellefonte, PA, USA), 60 m × 0.25 mmI.D., film thickness 0.25 μ m. The oven temperature was programmed at 35 ◦ C, held for 4 min, increased to 40 ◦ Cat 2 ◦ Cmin − 1 , held for 1 min, increased to 150 ◦ Cat 10 ◦ Cmin − 1 , held for 1 min, and increased to 250 ◦ Cat 5 ◦ Cmin − 1 . Helium was used as carrier gas at a flow rate of 1.0 mL min − 1 . High-resolution gas chromatography–mass spectrometry (HRGC–MS) measurements were performed using a GC-TOF-MS LECO model PEGASUS BT: mode EI+, 70 eV, source temperature 250 ◦ C,
https://doi.org/10.3390/s26072049
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