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Table2. Cont.
Sample
pH*
Sample
pH*
Sample
pH*
P6 P7
9.42 ± 0.02 9.01 ± 0.01
P13 P14
9.92 ± 0.01 9.82 ± 0.00
P20 P21
9.67 ± 0.00 9.71 ± 0.02
* Values expressed as mean ± standard deviation obtained from three measurements per replicate. As shown in Table 2, the samples had pH values between 9 and 10. The papers were produced between 2018 and 2019 (Table 1). Since the 1980s, to prevent paper degradation, free-acid paper has been produced using alkaline stock [19]. 3.2. Headspace Solid-Phase Micro-Extraction/Gas Chromatography–Mass Spectrometry (HS-SPME/GC–MS) Analysis Two types of SPME fibers were used in volatile analyses by HS-SPME/GC-MS. Figures S2 and S3 in the Supplementary Materials show the chromatograms obtained for sample P13 using a CAR/PDMS fiber and a PDMS fiber, respectively. Table 3 describes the main volatile compounds identified in samples using CAR/PDMS-SPME fiber. The VOCs were identified by comparing spectra with (NIST) library spectra and by matching the retention times to those of standards (pure compounds). Tables S1 and S2 (Supplementary Materials) describe the compounds identified in each paper sample using CAR/PDMS and PDMS SPME fibers, respectively.
Table3. Main VOCs identified in paper samples by HS-SPME-GC-MS using CAR/PDMS fiber.
Peak Number
Compound Identification
acetic acid
1 2 3 4 5 6 7 8 9
2-methoxyethanol
1-hydroxy-2-propanone
propanoic acid
3-hydroxybutanone
2,3-butanediol benzaldehyde
2,4,6-trimethylpyridine
benzyl alcohol
nonanal decanal
10 11
dodecanoic acid 1-methylethyl ester (isopropyl dodecanoate)
12
Figure 3 shows the volatile profiles of papers analyzed using the CAR/PDMS fiber (samples P1–P21, Table 1) and grouped by country of origin. The scale was the same across all the graphics to facilitate the visualization and comparison of results. Individual sample radial plots, as well as the summary table of all results, are provided in the (Supplementary Materials Table S1 and Figure S4, respectively).
https://doi.org/10.3390/s26072049
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