Final adjustments

The C6:EtOH 50:50 (1:1) extraction mixture was identified as the best compromise in order to extract at the same time MOSH and MOAH. It was then necessary to verify again the extraction length, previously verified with C6 (step 1). Therefore, the mixture was tested at RT for 1 h, 2 h, 5 h and 24 h. Focalizing on the different extraction times, differences are not great (see Figure 17). Therefore, the previously identified extraction length of 2 h at RT was confirmed as ideal.

EtOH 100%

C6 10% - EtOH 90%

C6 20% - EtOH 80%

C6 50% - EtOH 50%

C6 80% - EtOH 20%

Figure 17. MOSH LC-GC/FID chromatograms of: in black 1 h extraction, in pink 2 h, in blue 5 h and in green 24 h, all at RT and with an C6:EtOH 1:1 extraction mixture. No significant differences can be noticed at varying of extraction length.

Furthermore we wanted to determine whether variability in the part of packaging chosen for analysis (e.g. printed or not printed, shiny or opaque) could significantly affect the final result. For MOSH, Figure 18 shows the 1 and 2 h RT extraction of a shiny multicoloured paperboard part, the 2 h RT extraction of a white shiny part of the same paperboard and the 2 h RT extraction of a white opaque part. Confronting the extraction length of 1 or 2 h, it is clear that the second option gives a better extraction yield, thus confirming the choice of 2 h RT as the ideal extraction conditions. For MOAH there are no significant differences but the white opaque paperboard again shows a smaller amount of analytes in the first part of the chromatogram (see Figure 19).

Figure 18. MOSH LC-GC/FID chromatograms of: in black the 1 h RT extraction of a shiny multicoloured paperboard part of the packaging, in pink the 2 h RT one (more effective length of time), in blue the 2 h RT extraction of a white shiny part of the same paperboard and in green the 2 h RT extraction of a white opaque part: in green line, some of the analytes in the first part of the chromatogram are missing, so we can deduct they probably belong to the final shiny lacquering of packaging.

Figure 19. MOAH LC-GC/FID chromatograms of extraction with C6:EtOH 1:1 for 2 h at RT. The black line corresponds to the multicoloured board, the pink to the white shiny part and the blue to the white opaque part and: there are no significant differences but the opaque again shows a lesser in the first part of the chromatogram.

Overall, it can be concluded that length of extraction is not significantly affecting the final yield and kind of analytes extracted, whereas extracting mixture composition is the most important factor to take into account.

As a final example, Figures 20 and 21 show the MOSH and MOAH fraction chromatograms, respectively, from different paperboards, all extracted with the final optimized method.

Figure 20. LC-GC/FID chromatograms of MOSH: in black breakfast cereals with red fruits, in pink Luxemburgerli packaging, in blue Cappuccino ice cream cake, in green artisanal cake packaging. It can be distinguished clearly the two packaging made of recycled paper (higher contamination) from those made of virgin paper (lower contamination).

fresh fibres paper packaging

recycled fibres paper packaging

Figure 22. MOAH LC-GC/FID chromatograms: in pink the Luxemburgerli box (virgin paper, violet ink, opaque), in blue the Cappuccino ice cream cake box (virgin paper, multicoloured and shiny), in green the box for artisanal cakes (recycled paper, pink and blue inks) and in black the breakfast cereals with red fruits box again (recycled paper with multicolour inks and shiny finish).

For the first two it is noticeable the low amount of MOAH compared to the last two, very probably due to the recycled paper nature of them; for the Cappuccino box the DIPN (two big peaks plus sometimes minor peaks, depending on isomers proportion), typical recycling markers, are evident.

The final method for paperboard packaging analysis is as follow: 1 g ± 0.01 of paper/paperboard/corrugated board, finely cut into pieces, is weighed directly into a 20 mL screw top amber flask. A representative area of the pack (e.g. multicoloured portion of a coloured packaging) should be chosen. No gloves or hand cream were used during the sample manipulation and the flask caps had a PTFE inner surface to avoid external contamination. A mixture of hexane:ethanol (10 mL) 1:1 by volume is added into the flask to the board pieces, along with 20 µ L of internal standards solution for mineral oil hydrocarbons. The flask is closed tightly and vortexed for 5 s, then left for 2 h at RT. After that time, ca. 10 mL of water is added into the flask, ensuring thorough mixing by manually shaking or vortexing. The water ensures the removal of ethanol from hexane owing to the polar character of the protonated solvents. After separation of the two phases (hexane and hydroalcoholic solution) obtained either by allowing 10 min time or by

DIPN

fresh fibres paper packaging

recycled fibres paper packaging

centrifugation, the upper hexane phase is removed and then washed again with water in a separate and clean glass flask, to ensure complete removal of ethanol that would be detrimental to the chromatographic analyses. Finally, ca. 1 mL of the clean hexane extract is transferred into autosampler vials for the chromatographic analysis, ensuring the vial cup is well tight to avoid any solvent loss through evaporation. For the same reason, vials are better kept into a refrigerator if not immediately analyzed.

For plastic extraction, the same method was used except for sample weight: only 0.2 g of sample was weighed instead of 1 g, due to the often higher mineral oil contamination of plastic compared to paperboard, along with the presence of polyolefin oilgomeric saturated hydrocarbons (POSH), as typical plastic oligomers.

This extraction method has also been successfully applied to other paperboard contaminants, such as phthalates and other plasticizers, photoinitiators, rosin components, etc. The same extract can be analyzed by LC-GC/FID for MOSH, MOAH and DIPN and in GC/MS for all those other contaminants (data not shown in this thesis), making optimal use of one single extraction.

4.1.2 FOOD EXTRACTION

Food extraction approach is very different depending on food moisture content. Dry food can easily be extracted with pure hexane, which has very high chemical affinity for MOSH and MOAH. In the case of moist or liquid foods (frozen foods, eggs, teas, but also foods considered quite “dry” as dry plums and apricots), the presence of water in the food matrix hinders the hexane capacity to extract the mineral oil contaminants, so a more complex extraction procedure must be applied.